Allegory of the senses by Jan Brueghel the Elder, Museo del Prado

An odor or odour (commonly referred to as a smell) is caused by one or more volatilized chemical compounds, generally at a very low concentration, that humans or other animals perceive by the sense of olfaction. Odors are also commonly called scents, which can refer to both pleasant and unpleasant odors. The terms fragrance and aroma are used primarily by the food and cosmetic industry to describe a pleasant odor, and are sometimes used to refer to perfumes. In contrast, malodor, stench, reek, and stink are used specifically to describe unpleasant odors.

Terminology[link]

In the United Kingdom, odour refers to scents in general. In the United States, odor has a more negative connotation, such as smell, stench or stink, while scent or aroma are used for pleasant smells.

Basics[link]

The sense of smell gives rise to the perception of odors, mediated by the olfactory nerve. The olfactory receptor (OR) cells are neurons present in the olfactory epithelium, a small patch of tissue in back of the nasal cavity. There are millions of olfactory receptor neurons that act as sensory signaling cells. Each neuron has cilia in direct contact with air. The olfactory nerve is considered the smell mediator, the axon connects the brain to the external air. Odorous molecules act as a chemical stimulus. Molecules bind to receptor proteins extended from cilia, initiating an electric signal.

The primary sequences of thousands of olfactory receptors are known from the genomes of more than a dozen organisms: they are seven-helix transmembrane proteins, but there are (as of July 2011) no known structures of any OR. There is a highly conserved sequence in roughly three quarters of all ORs that is a tripodal metal ion binding site,^[1] and Suslick has proposed that the ORs are in fact metalloproteins (most likely with zinc, copper and possibly manganese ions) that serve as a Lewis Acid site for binding of many odorant molecules. Crabtree, in 1978, had previously suggested that Cu(I) is "the most likely candidate for a metallo-receptor site in olfaction" for strong-smelling volatiles which are also good metal-coordinating ligands, such as thiols.^[2] Zhang, Matsunami and Block, in 2012, confirmed the Crabtree/Suslick proposal for the specific case of a mouse OR, MOR244-3, showing that copper is essential for detection of certain thiols and other sulfur-containing compounds. Thus, by using a chemical that binds to copper in the mouse nose, so that copper wasn’t available to the receptors, the authors showed that the mice couldn't detect the thiols. However, these authors also found that MOR244-3 lacks the specific metal ion binding site suggested by Suslick, instead showing a different motif in the EC2 domain.^[3]

When the signal reaches a threshold, the neuron fires, sending a signal traveling along the axon to the olfactory bulb, part of the limbic system of the brain. Interpretation of the smell begins, relating the smell to past experiences and in relation to the substance(s) emitted. The olfactory bulb acts as a relay station connecting the nose to the olfactory cortex in the brain. Olfactory information is further processed and projected through a pathway to the central nervous system (CNS), which controls emotions and behavior as well as basic thought processes.

Odor sensation depends on the concentration (number of molecules) available to the olfactory receptors. A single odorant stimulus type is typically recognized by multiple receptors, and different odorants are recognized by combinations of receptors, the patterns of neuron signals helping to identify the smell. The olfactory system does not interpret a single compound, but instead the whole odorous mix, not necessarily corresponding to concentration or intensity of any single constituent.^[4][5]

The widest range of odors consists of organic compounds, although some simple compounds not containing carbon, such as hydrogen sulfide and ammonia, are also odorants. The perception of an odor effect is a two-step process. First, there is the physiological part; the detection of stimuli by receptors in the nose. The stimuli are processed by the region of the human brain which is responsible for olfaction. Because of this, an objective and analytical measure of odor is impossible. While odor feelings are very personal perceptions, individual reactions are related to gender, age, state of health, and personal history.

Common odors that people are used to, such as their own body odor, are less noticeable to individuals than external or uncommon odors. This is due to habituation; after continuous odor exposure, the sense of smell fatigues quickly, but recovers rapidly after the stimulus is removed.^[6] Odors can change due to environmental conditions, for example odors tend to be more distinguishable in cool dry air.^[7]

Habituation affects the ability to distinguish odors after continuous exposure. The sensitivity and ability to discriminate odors diminishes with exposure, and the brain tends to ignore continuous stimulus and focus on differences and changes in a particular sensation. When odorants are mixed, the conditioned odorant is blocked out because of habituation. This depends on the strength of the odorants in the mixture which can change perception and processing of an odor. This process helps classify similar odors as well as adjust sensitivity to differences in complex stimuli.^[8]

For most untrained people, the process of smelling gives little information concerning the specific ingredients of an odor. Their smell perception primarily offers information related to the emotional impact.^{[citation needed]} Experienced people, however, such as flavorists and perfumers, can pick out individual chemicals in complex mixes through smell alone.

Odor perception is a primal sense. The sense of smell enables pleasure, can subconsciously warn of danger, help locate mates, find food, or detect predators. Humans have a surprisingly good sense of smell (even though they only have 350 functional olfactory receptor genes compared to the 1,300 found in mice) correlated to an evolutionary decline in sense of smell. Humans remarkable sense of smell is just as good as many animals, and can distinguish a diversity of odors- approximately 10,000 scents. This is because of the retro nasal route in humans to increase sensation.^{[further explanation needed]} However, animals such as dogs show a greater sensitivity to odors than humans especially in studies using short-chained compounds. Higher cognitive brain mechanisms and more olfactory brain regions enable humans to discriminate odors better than other mammals despite fewer olfactory receptor genes.^[9]

It has been proposed that there are seven primary odors: (with examples)^[10][11]

1. Musky- perfumes/aftershave
2. Putrid- rotten eggs
3. Pungent- vinegar
4. Camphoraceous- mothballs
5. Ethereal- dry cleaning fluid
6. Floral- roses
7. Pepperminty- mint gum

Odor analysis[link]

The ability to identify odors varies among people and decreases with age. Studies show there are sex differences in odor discrimination; women usually outperform males.^[12] Pregnant women also have increased smell sensitivity, sometimes resulting in abnormal taste and smell perceptions, leading to food cravings or aversions.^[13] Deficits in smell also increase with age as well as a prevalence of taste problems (the sense of smell tends to dominate the sense of taste). Chronic smell problems are reported in small numbers for those in their mid-twenties, with numbers increasing steadily with overall sensitivity beginning to decline in the second decade of life, and then deteriorating appreciably as age increases to over 70 years of age.^[14]

In Germany, the concentrations of odorants have since the 1870s been defined by "Olfaktometrie", which helps to analyze the human sense of smell using the following parameters: odor substance concentration, intensity of odor, and hedonic assessment.

To establish the odor concentration, an olfactometer test is used, which employs a panel of human noses as sensors. In the olfactometry testing procedure, a diluted odorous mixture and an odor-free gas (as a reference) are presented separately from sniffing ports to a group of panelists, who are housed in an odor-neutral room. They are asked to compare the gases emitted from each sniffing port, after which the panelists are asked to report the presence of odor together with a confidence level such as guessing, inkling, or certainty of their assessment. The gas-diluting ratio is then decreased by a factor of two (i.e. chemical concentration is increased by a factor of two). The panelists are then asked to repeat their judgment. This continues for a number of dilution levels. The responses of the panelists over a range of dilution settings are used to calculate the concentration of the odor in terms of European Odor Units (ouE/m³). The main panel calibration gas used is Butan-1-ol, which at a certain diluting gives 1 ouE/m³.

General survey[link]

The analytic methods could be subdivided into the physical, the gas chromatographical, and the chemosensory method.

When measuring odor, there is a difference between emission and immission measurements. Emission measurement can be conducted by olfactometry using an olfactometer to dilute the odor sample. On the contrary, olfactometry is rarely used for immission measurement because of the low odor concentrations. The same measuring principals are used, but the judgment of the air assay happens without diluting the samples.

Measurement[link]

An electronic nose tuned to distinguish between odors pleasant to humans (e.g. a rose) or unpleasant (e.g. a skunk).

Different aspects of odor can be measured through a number of quantitative methods, such as assessing concentration or apparent intensity.

Initial entry into a room provides the most accurate sensing of smell, before habituation begins to change perception of odor.

Sensation of odor has 4 properties related to threshold and tolerance: Odor concentration, odor intensity, odor quality, and hedonic tone

Measuring odor concentration[link]

Odor concentration is an odor's pervasiveness. To measure odor sensation, an odor is diluted to certain amounts to reach a detection or recognition threshold. The detection threshold is the concentration of an odor in air when 50% of a population can distinguish between the odorous sample and an odor free blank. The recognition threshold is the concentration of an odor in air in which 50% of a population can discern from an odorous sample and odor free blank.The recognition odor threshold is usually a factor of 2 to 5 times higher than the detection threshold.^[10]

The measurement of odor concentration is the most widespread method to quantify odors. It is standardized in CEN EN 13725:2003.^[15] The method is based on dilution of an odor sample to the odor threshold (the point at which the odor is only just detectable to 50 % of the test panel). The numerical value of the odor concentration is equal to the dilution factor that is necessary to reach the odor threshold. Its unit is the European Odor Unit, OU_E. Therefore, the odor concentration at the odor threshold is 1 OU_E by definition.

To establish the odor concentration, an olfactometer is used which employs a group of panelists. A diluted odorous mixture and an odor-free gas (as a reference) are presented from sniffing ports to a group of panelists. In comparing the odor emitted from each port, the panelists are asked to report if they can detect a difference between the ports. The gas-diluting ratio is then decreased by a factor of 1.4 or two (i.e. the concentration is increased accordingly). The panelists are asked to repeat their judgment. This continues until the panelists respond certain and correct twice in a row. These responses are used to calculate the concentration of the odor in terms of European Odor Units (OU_E/m³).

The test persons must fulfill certain requirements, for example regarding their sensitivity of odor perception. The main panel calibration gas to verify this requirement used is n-Butanol (as 1 OU_E/m³≡40 ppb/v n-butanol).^[16]

To collect an odor sample, the samples must be collected using specialized sample bags, which are made from an odor free material e.g. Teflon. The most accepted technique for collecting odor samples is the lung technique, where the sample bag is placed in a sealed drum, and a vacuum is placed on the drum, which fills the sample bag as the bag expands, and draws the sample from the source into the bag. Critically, all components which touch the odor sample, must be odor free, which includes sample lines and fittings.

A human's odor detection threshold is variable. Repeated exposure to an odorant leads to enhanced olfactory sensitivity and decreased detection thresholds for a number of different odorants.^[17] It was found in a study that humans that were completely unable to detect the odor of androstenone developed the ability to detect it after repeated exposure.^[18]

Humans can discriminate between two odorants that differ in concentration by as little as 7%.^[19]

There are a number of issues which have to be overcome with sampling, these include: - If the source is under vacuum - if the source is at a high temperature - If the source has high humidity

Issues such as temperature and humidity are best overcome using either pre-dilution or dynamic dilution techniques.

Odor intensity[link]

Odor intensity is the perceived strength of odor sensation. This intensity property is used to locate the source of odors and perhaps most directly related to odor nuisance.^[5]

Perceived strength of the odor sensation is measured in conjunction with odor concentration. This can be modeled by the Weber-Fechner law: I= a * log(c)+b^[20]

I is the perceived psychological intensity at the dilution step on the butanol scale, a is the Weber-Fechner coefficient, C is the chemical concentrations, and b is the intercept constant (0.5 by definition)^[20]

Odor intensity can be expressed using an odor intensity scale, which is a verbal description of an odor sensation to which a numerical value is assigned.^[20]

Odor intensity can be divided into the following categories according to intensity:

0 - no odor

1 - very weak (odor threshold)

2 - weak

3 - distinct

4 - strong

5 - very strong

6 - intolerable

This method is applied by in the laboratory and is done so by a series of suitably trained panelists/observers who have been trained to appropriately define intensity.

Hedonic Tone Assessment[link]

Hedonic assessment is the process of scaling odors on a scale ranging from extremely unpleasant via neutral up to extremely pleasant. It is important to note that intensity and hedonic tone, whilst similar, refer to different things. That is, the strength of the odor (intensity) and the pleasantness of an odor (hedonic tone). Moreover, it is important to note that perception of an odor may change from pleasant to unpleasant with increasing concentration, intensity, time, frequency, and previous experience with a specific odor; all factors determining a response.^[21] The overall set of qualities are sometimes identified as the "FIDOL factors", short for Frequency, Intensity, Duration, Offensiveness and Location.^[22]

Odor character[link]

The character of an odor is a critical element in assessing an odor. This property is the ability to distinguish different odors and is only descriptive. First a basic description is used such as sweet, pungent, acrid, fragrant, warm, dry, or sour. The odor is then referenced to a source such as sewage or apple which can then be followed by a reference to a specific chemical such as acids or gasoline.^[5]

Most commonly, a set of standard descriptors is used, which may range from fragrant to sewer odor.^[23] Although the method is fairly simplistic, it is important for the FIDOL factors to be understood by the person recording the character. This method is most commonly used to define the character of an odor which can then be compared to other odors. It is common for olfactometry laboratories to report character as an additional factor post sample analysis.

Interpreting dispersion modeling[link]

In many countries odor modeling is used to determine the extent of an impact from an odor source. These are a function of modeled concentration, averaging time (over what time period the model steps are run over (typically hourly) and a percentile. Percentiles refer to a statistical representation of how many hours per year, the concentration C may be exceeded based on the averaging period.

Sampling from area sources[link]

There are two main odor sampling techniques, the direct odor sampling and the indirect odor sampling technique. Indirect refers to collecting samples from the air stream which has already passed over the emitting surface.

Direct sampling[link]

Direct refers to the placement of a enclosure on or over an emitting surface from which samples are collected, and an odor emission rate is determined.

The most commonly used direct methods include the Flux Chamber^[24] and wind tunnels which include the UNSW Wind tunnel.^[25] There are many other available techniques, and consideration should be given to a number of factors before selecting a suitable method.

A source which has implications for this method are sources such as bark bed biofilters, which have a vertical velocity component. For such sources, consideration needs to be given as to the most appropriate method. A commonly used technique is to measure the odor concentration at the emitting surface, and combine this with the volumetric flow rate of air entering the biofilter to produce an emission rate.

Indirect odor sampling[link]

Indirect sampling is often referred to as back calculation. It involves the use of a mathematical formula to predict an emission rate.

Many methods are used, but all make use of the same inputs which include - Surface roughness - Upwind and down wind concentrations - Stability class (or other similar factor) - Wind speed and direction

Odor in the Indoor Environment[link]

The human sense of smell is a primary factor in the sensation of comfort. Olfaction as a sensory system brings awareness of the presence of airborne chemicals. Some inhaled chemicals are volatile compounds that act as a stimulus, triggering unwanted reactions such as nose, eye, and throat irritation. Perception of odor and of irritation is unique to each person, and varies over because of physical conditions or memory of past exposures to similar chemicals. A person's specific threshold before an odor becomes a nuisance depends also on the frequency, concentration, and duration of an odor.

The perception of irritation from odor sensation is hard to investigate because exposure to a volatile chemical elicits a different response based on sensory and physiological signals, and interpretation of these signals influenced by experience, expectations, personality or situational factors. Volatile organic compounds (VOCs) may have higher concentrations in confined indoor environments due to restricted infiltration of fresh air, as compared to the outdoor environment; leading to greater potential for toxic health exposures from a variety of chemical compounds. Health effects of odor are traced to the sensation of an odor or the odorant itself. Health effects and symptoms vary, including eye, nose, or throat irritation, cough, chest tightness, drowsiness, and mood change; all of which decrease as an odor ceases. Odors may also trigger illnesses such as asthma, depression, stress induced illness, or hypersensitivity. Ability to perform tasks may decrease, and other social/behavioral changes may occur.

Occupants should expect remediation from disturbing and unexpected odors that disturb concentration, diminish productivity, evoke symptoms, and generally increase the dislike for a particular environment. It is important to set occupational exposure limits (OELs) to ensure the health and safety or workers as well as comfort, because exposure to chemicals can elicit physiological and biochemical changes in the upper respiratory system. Standards are hard to set when exposures are not reported and can also be hard to measure. Work force populations vary in levels of discomfort from odors because of exposure history or habituation, and they may not realize possible risks of exposure to chemicals that produce specific odors.^[26][27]

Legislative provisions associated with odors[link]

This unreferenced section requires citations to ensure verifiability.

While developing environmental legislation in Germany, it was noted that there was a need for a method to accurately measure odor. Since that time, the following laws have been established:

1. "refinery guideline" (early 1970s)
2. federal emission protection law (1974)
3. technical guideline to keep the air fresh
4. olfactory emission guideline (early 1980s until 1998)

Barriers around the sources of the odors have turned out to be badly feasible. Ramparts, plantings etc. are little effective, whereas plantations are, after all, often at least perceived as a remarkable factor.

The only workable principle is, so far, to place the sources of the odors far enough from anybody who could feel disturbed, and to pay attention to the prevailing wind direction. Also diluting the emissions with a large air flow promises so be an effective way to avoid complicated and expensive technical measures.

Encapsulating of olfactorily relevant asset areas is only theoretically the ideal method to reduce the emission. Within an enclosure, damp and an oppressive atmosphere can arise, so that the inner materials of the capsule produce a strong mechanical stress. Encapsulating even brings about a noteworthy explosion hazard.

For encapsulation to be viable, there must be some way to exhaust the spent air. Odorants remain inside the medium and tend to leak at the next suitable spot. The encapsulated space is never really gas-proof, and at some spots substances may leak out at considerably higher concentrations than they would do without the made efforts to hold them back.

There are three different ways exhausted air may be treated:

• chemical treatment
• physical treatment
• biological treatment

Adsorption as separating process[link]

Adsorption is a thermodynamic separation process, which is characterized by the removal of molecules out of a fluid phase at a solid surface. Molecules of a gaseous or fluid mixture are selectively taken up by a solid with a porous interface surface. The solid matter is called the adsorbant, the adsorbed fluid is called the adsorbate. There are two types of adsorption, physisorption and chemisorption. The type of force driving the adsorption process is different between the two.

Physisorption[link]

A special type of adsorption is physisorption. The difference between physisorption and chemisorption is that the adsorbed molecule is tied up with the substrate by physical forces, defined here as forces which do not cause chemical bonds. Such interactions are mostly unfocused in contrast to chemical bonds. "Van-Der-Waals" – forces are a special type of such physical forces. These forces are characterized by electrostatic interactions between induced, fluctuating dipoles. To be more specific you have to call those forces "London's Dispersal forces." A so called dipole moment occurs because of fluctuations in the distribution of electrons around individual atoms. The temporary mean value of this force is however zero. Even though it’s only a mere transient dipole moment, this moment can cause a nonparallel dipole moment in an adjacent molecule. Operating forces of this nature are in inverse proportion to the sixth power of the distance between those molecules. These forces occur in almost every chemical system, but are relatively weak.

Physisorption is an exothermic and reversible reaction. Obviously stronger strengths accrue through the interaction between solid dipoles at polar surfaces or reflexive loadings, appearing in electric conductive surfaces. Such interactions could be defined as a chemisorption because of their strength.

Chemisorption[link]

In many reactions, physisorption is a pre-cursor to chemisorption. Compared to physisorption, chemisorption is not reversible and requires a larger activation energy. Usually the bond energy is about 800 kJ/mol. For physisorption the bond energy is only about 80 kJ/mol. A monomolecular layer could be maximally adsorbed. Strong bonds between the adsorbative molecules and the substrate could lead to the point that their intermolecular bonds partly or completely detach. In such a case you have to call this a dissociation. Those molecules are in a highly reactive state. This is the basis of heterogeneous catalysis. The substrate is then called catalytic converter. The differences between Chemisorption and Physisorption extends beyond an increased activation energy. An important criteria for chemisorption is the chemical mutation of the absorbent. Thereby it is possible that you have to deal with a chemisorption in a few combinations with a relatively low bond energy, for example 80 kJ/mol, as a physisorption could be another combination with a bond energy even by 100 kJ/mol. The interaction with different adsorbative molecules is very different. The surface could be taken by substances, which point out a very high bond energy with the substrate, and as a consequence of this the wanted reaction is impossible. Because of that feature those substances are called catalytic converter venom. Heat is released during that process too.

Loading of the adsorbate[link]

During the adsorption of a molecule, energy — the heat of adsorption — is released. This energy is the difference of the enthalpy of the adsorbate in the fluid or gaseous phase and the its corresponding enthalpy on the surface of the adsorbant. With an increase of adsorbate loading on the surface of the adsorbant, the bond energy decreases in the area of the monomolecular covering. For higher loading, this value approaches zero. This implies that there is a limit for the loading of an adsorbate. (The procedure of reversing that process is called desorption). Adsorption as a separating process is a challenging process, in the case of finding the eligible adsorbates, which could link as multilateral as possible.

Types of odors[link]

Some odors such as perfumes and flowers are sought after, with elite varieties commanding high prices. Whole industries have developed around products to remove unpleasant odors (see deodorant). The perception of odors is also very much dependent upon circumstance and culture. The odor of cooking processes may be pleasurable while one is cooking, but not necessarily after the meal.

The odor molecules transmit messages to the limbic system, the area of the brain that governs emotional responses. Some believe that these messages have the power to alter moods, evoke distant memories, raise their spirits, and boost self-confidence. This belief has led to the concept of "aromatherapy" wherein fragrances are claimed to cure a wide range of psychological and physical problems. Aromatherapy claims that fragrances can positively affect sleep, stress, alertness, social interaction, and general feelings of well-being. However, the evidence for the effectiveness of aromatherapy consists mostly of anecdotes and lacks controlled scientific studies to back up its claims.

With some fragrances, such as those found in perfume, scented shampoo, scented deodorant, or similar products, people can be allergic to the ingredients. The reaction, as with other chemical allergies, can be anywhere from a slight headache to anaphylactic shock, which can result in death.^{[citation needed]}

Unpleasant odors play various roles in nature, often to warn of danger, though this may not be known to the subject who smells it.^[28] An odor that is viewed as unpleasant by some people or cultures can be viewed as attractive by others where there is more familiarity or a better reputation.^[28]

It is commonly viewed^{[by whom?]} that those holding an unpleasant body odor will be unattractive to others. But studies have shown that a person who is exposed to a particular unpleasant odor can be attracted to others who have been exposed to the same unpleasant odor.^[28] This includes smells associated with pollution.^[28]

What actually causes a substance to smell unpleasant may be different from what one perceives. For example, perspiration is often viewed as having an unpleasant odor, but it is actually odorless. It is the bacteria in the perspiration that cause the odor.^[29]

Unpleasant odors can arise from specific industrial processes, adversely affecting workers and even residents downwind of the industry. The most common sources of industrial odor arise from sewage treatment plants, refineries, animal rendering factories, and industries processing chemicals (such as sulfur) which have odorous characteristics. Sometimes industrial odor sources are the subject of community controversy and scientific analysis.

Body odor is present both in animals and humans and its intensity can be influenced by many factors (behavioral patterns, survival strategies). Body odor has a strong genetic basis both in animals and humans, but it can be also strongly influenced by various diseases and psychological conditions.

Study of odors[link]

The study of odors is a growing field but is a complex and difficult one. The human olfactory system can detect many thousands of scents based on only very minute airborne concentrations of a chemical. The sense of smell of many animals is even better. Some fragrant flowers give off odor plumes that move downwind and are detectable by bees more than a kilometer away.

The study of odors can also get complicated because of the complex chemistry taking place at the moment of a smell sensation. For example iron-containing metallic objects are perceived to have a distinctive odor when touched, although iron's vapor pressure is negligible. According to a 2006 study^[30] this smell is the result of aldehydes (for example nonanal) and ketones (example: 1-octen-3-one) released from the human skin on contact with ferrous ions that are formed in the sweat-mediated corrosion of iron. The same chemicals are also associated with the smell of blood, as ferrous iron in blood on skin produces the same reaction.

Pheromones[link]

Pheromones are odors that are used for communication, and are sometimes called "airborne hormones". A female moth may release a pheromone that can entice a male moth that is several kilometers downwind. Honeybee queens constantly release pheromones that regulate the activity of the hive. Workers can release such smells to call other bees into an appropriate cavity when a swarm moves into new quarters, or to "sound" an alarm when the hive is threatened.

Advanced technology[link]

There are hopes that advanced technology could do everything from testing perfumes to helping detect cancer or explosives by detecting specific scents, but as of yet artificial noses are still problematic. The complex nature of the human nose, its ability to detect even the most subtle of scents, is at the present moment difficult to replicate.

Most artificial or electronic nose instruments work by combining output from an array of non-specific chemical sensors to produce a finger print of whatever volatile chemicals it is exposed to. Most electronic noses need to be "trained" to recognize whatever chemicals are of interest for the application in question before it can be used. The training involves exposure to chemicals with the response being recorded and statistically analyzed, often using multivariate analysis and neural network techniques, to "learn" the chemicals. Many current electronic nose instruments suffer from problems with reproducibility subject to varying ambient temperature and humidity. An example of this type of technology is the colorimetric sensor array, which visualizes odor through color change and creates a "picture" of it.^{[31] [32][33][34][35][36]}

Behavioral cues[link]

Odor perception is a complex process involving the central nervous system that can evoke psychological and physiological responses. Because the olfactory signal terminates in or near the amygdala odors are strongly linked to memories and can evoke emotions. The amygdala participates in the hedonic or emotional processing of olfactory stimuli.^[37] Odors can disturb our concentration, diminish productivity, evoke symptoms, and, in general, increase a dislike for a particular environment. Odors can impact the liking for a person, place, food, or product as a form of conditioning.^[38] Memories recalled by odors are significantly more emotional and evocative than those recalled by the same cue presented visually or auditorily.^[39] Odors can become conditioned to experiential states and when later encountered have directional influences on behavior. Doing a frustrating task in a scented room decreases performance of other cognitive tasks with the presence of the same odor.^[40] Nonhuman animals communicate their emotional states through changes in body odor and human body odors are indicative of emotional state.^[41]

Human body odors influence interpersonal relationships. Human body odors are involved in adaptive behaviors, such as parental attachment in infants or partner choice in adults. "Mothers can discriminate the odor of their own child, and infants recognize and prefer the body odor of their mother over that of another woman. This maternal odor appears to guide infants toward the breast and to have a calming effect." Body odor is involved in the development of infant–mother attachment and is essential to a child’s social and emotional development bringing feelings of security. Reassurance created by familiar parental body odors may contribute significantly to the attachment process.^[42]

How a man smells is critical for woman to find a lover. Body odor is a sensory cue critical for mate selection because it is a signal of immunological health. Women prefer men with major histocompatibility complex (MHC) genotypes and odor different than themselves especially during ovulation. Different MHC alleles are favorable because different allele combinations would maximize disease protection and minimize recessive mutations in offspring. Biologically females tend to select mates "who are most likely to secure offspring survival and thus increase the likelihood that her genetic contribution will be reproductively viable." ^[43]

Studies have suggested that people might be using odor cues associated with the immune system to select mates. Using a brain imaging technique, Swedish researchers have shown that gay and straight males' brains respond differently to two odors that may be involved in sexual arousal, and that the gay men respond in the same way as straight women, though it could not be determined whether this was cause or effect. The study was expanded to include lesbian women; the results were consistent with previous findings meaning that lesbian women were not as responsive to male identified odors, while their response to female cues was similar to straight males.^[44] According to the researchers, this research suggests a possible role for human pheromones in the biological basis of sexual orientation.^[45]

An odor can cue recall of a distant memory. Most memories that pertain to odor come from the first decade of life, compared to verbal and visual memories which usually come from the 10th to 30th years of life.^[46] Odor-evoked memories are more emotional, associated with stronger feelings of being brought back in time, and have been thought of less often as compared to memories evoked by other cues.^[47]

Use of scent in design[link]

The sense of smell is often overlooked as a way of marketing products. The deliberate and controlled application of scent is used by designers, scientists, artists, perfumers, architects and chefs. Some applications of scents in environments are in casinos, hotels, private clubs and new automobiles. For example, "technicians at New York City’s Sloan-Kettering Cancer Center disperse vanilla-scented oil into the air to help patients cope with the claustrophobic effects of MRI testing. Scents are used at the Chicago Board of Trade to lower the decibel level on the trading floor." ^[48]

The "new car smell" is not intentionally produced by the manufacturer, but is the smell "of number of harmful chemicals, including [the elements] antimony, bromine, chlorine, and lead. Repeated and concentrated exposure to any of these chemicals may contribute to a variety of acute and long-term health issues such as birth defects, impaired learning, liver toxicity, and cancer." ^[49]

Currently there is no regulation of the use of scent in product design. The FDA has no say as to what items are used to create a scent. If ingredients are listed on a product, the term "fragrance" can be used in a general sense. The National Academy of Sciences (NAS) reports that "95 percent of the ingredients used to create fragrances today are synthetic compounds derived from petroleum, including benzene derivatives, aldehydes, and many other known toxins and sensitizers. Many of these substances have been linked to cancer, birth defects, central nervous system disorders, and allergic reactions." ^[50]

See also[link]

• Aroma compound
• Machine olfaction
• Olfaction
• Olfactometer
• Olfactory fatigue
• Scented water

Notes[link]

References[link]

Further reading[link]

• Gilbert, Avery (2008). What the nose knows : the science of scent in everyday life (1st ed.). New York: Crown Publishers. ISBN 978-1-4000-8234-6. 
• Kaye, Joseph Nathaniel (May 2001). "Symbolic Olfactory Display (Master's Thesis)". Symbolic Olfactory Display. Massachusetts Institute of Technology. http://alumni.media.mit.edu/~jofish/thesis/symbolic.olfactory.display.pdf. Retrieved 2011-06-25.  — A survey of current olfactory knowledge, experimental investigation of computer-based olfactory interfaces. Includes extensive reference list, partially annotated.
• Samet, edited by Jonathan M.; Spengler, John D. (1991). Indoor air pollution : a health perspective. Baltimore: Johns Hopkins University Press. ISBN 978-0-8018-4125-5. 
• Watson, Lyall (2000). Jacobson's organ and the remarkable nature of smell (1st American ed.). New York: W.W. Norton. ISBN 978-0-393-04908-4. 

External links[link]

Look up odor in Wiktionary, the free dictionary.

• Answers to several questions from curious kids about smells and odors
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Terry Crews
Crews at the San Diego Comic-Con International in July 2010
Born	Terrence Alan Crews (1968-07-30) July 30, 1968 (age 43) Flint, Michigan, U.S.
Other names	Terry Alan Crews, Big T, T-Money, Squeegee Lo, Henry David Thoreau, Terry Crews, Jr.
Occupation	Football player (1991-1996) Actor, comedian, voice artist (1999–present)
Years active	1999–present
Spouse	Rebecca Crews (1990–present) 5 children
Website
http://www.terrycrews.com/

Terrence Alan "Terry" Crews (born July 30, 1968) is an American actor, comedian, voice artist and a former player in the National Football League. He is perhaps best known for his role as family patriarch Julius on the UPN/CW sitcom Everybody Hates Chris. Currently, he stars in the TBS sitcom Are We There Yet? as Nick Kingston-Persons. Additionally, he stars in the BET reality series The Family Crews, and has appeared in such films as The 6th Day, Friday After Next, White Chicks, Idiocracy and The Expendables.

In 2010 Crews was featured in several Old Spice TV commercials for their "Odor Blocker Body Wash", and in 2012 for their body spray, directed by Tim Heidecker and Eric Wareheim.

Early life[link]

Crews was born in Flint, Michigan,^[1] the son of Patricia and Terry Crews, Sr. He attended Flint Southwestern Academy.^[2] He earned an Art Excellence Scholarship to attend the Interlochen Center for the Arts and then Western Michigan University.^[3]

While completing his studies as hop an Art major, Crews was a key member of the WMU football team, where he earned all-conference honors as a defensive end. Crews was drafted by the Los Angeles Rams of the NFL in the 11th round of the 1991 NFL Draft.^[4] He carved out a career that lasted seven^[5] seasons, including stints with the Rams, San Diego Chargers, the Washington Redskins and the Philadelphia Eagles.

Career[link]

After retiring from the NFL in 1997, Crews pursued an acting career and took a stint as T-Money on Battle Dome (modeled after American Gladiators). Crews played the beefcake "he-man" in movies, such as White Chicks. Crews also played Damon Pearly in Friday After Next, starring Ice Cube and Mike Epps. He has also done commercials with Nike. He last starred in the sitcom Everybody Hates Chris as Julius Rock, and his more modern movie appearances were alongside Adam Sandler in The Longest Yard, Click, and The Benchwarmers (as well as the long-delayed Mike Judge film Idiocracy, where Crews played President Dwayne Elizondo Mountain Dew Herbert Camacho).

Crews has made many cameo appearances. He was in blink-182's music video of Down as a police officer, in Jamie Kennedy's Rollin' with Saget as the security guard, and in films such as Training Day and Soul Plane.

Crews usually portrays buff-looking characters with a humorous softer side, singing along with 80's music or becoming engaged with soap operas (as well as his signature robot dance). But more recently, he has been able to alternate with more serious projects such as his recent appearances in Harsh Times, Street Kings and the action movie, The Expendables.

He has been featured recently in several Old Spice TV commercials for their "Odor Blocker Body Wash". The ads were directed by Tim Heidecker and Eric Wareheim.

In the sitcom Are We There Yet?, Crews had a lead role as Nick Kingston-Persons. In the series' first trailer, Ice Cube said that Crews is the perfect person to replace him as Nick, and that his physical comedy is undeniable. The series was picked up for 90 new episodes^[6] (approx six seasons) by August 2010, while Crews enjoyed box office success in three movies in August 2010 (Middle Men, The Expendables, Lottery Ticket).^[7]

He also stars in his own reality series on BET entitled The Family Crews which is about his everyday life with his family. The show premiered on February 21, 2010.

Personal life[link]

Crews at the 79th Annual Academy Awards Children Uniting Nations/Billboard afterparty.

Crews has four daughters and one son (with one being a stepdaughter from his wife's previous relationship) with his wife of 22 years, Rebecca King-Crews, a former beauty queen and gospel recording artist.

Filmography[link]

Television work[link]

• Battle Dome - T-Money (1999–2001)
• Everybody Hates Chris - Julius (2005–2009)
• My Wife and Kids - Daryl (2005; Guest star)
• The Boondocks - Multiple characters (voice) (2006; Guest star)
• Are We There Yet? - Nick Kingston-Persons (2010–present)
• The Family Crews - Himself (2010–present)

Music videos[link]

• Blink-182 - "Down" - Police Officer (2004)

References[link]

External links[link]

Wikimedia Commons has media related to: Terry Crews

• Official website
• Terry Crews at the Internet Movie Database
• BET Shows - The Family Crews Website
• Squeegee Lo Website
• NFL stats at Databasefootball.com
• Terry Crews reality show - The Family Crews

Billy Mays
Mays at Flatiron District in June 2009, a few weeks before his death
Born	William Darrell Mays, Jr. (1958-07-20)July 20, 1958[1] McKees Rocks, Pennsylvania, United States
Died	June 28, 2009(2009-06-28) (aged 50) Tampa, Florida, United States
Other names	Billy Mays, King of the Pitch
Occupation	Television direct-response advertisement salesman
Years active	1993–2009
Home town	McKees Rocks, Pennsylvania
Spouse	Dolores "Dee Dee" Mays[2] Deborah Mays[2]
Children	Billy Mays III Elizabeth Mays
Parents	Billy Mays, Sr. Joyce Palm

William Darrell "Billy" Mays, Jr. (July 20, 1958 – June 28, 2009)^[3] was an American television direct-response advertisement salesperson most notable for promoting OxiClean, Orange Glo, and other cleaning, home-based, and maintenance products on the Home Shopping Network, and through his company, Mays Promotions, Inc. He and his business partner, Anthony Sullivan, were also featured on PitchMen, a TV series that documented their work. His distinctive beard and impassioned sales pitches made him a recognized television presence in the United States and Canada.^[4][5] Mays was found unresponsive by his wife in his Tampa, Florida, home on the morning of June 28, 2009.^[6] He was pronounced dead at 7:45 am, appearing to have died sometime overnight.^[3][7]

Early life[link]

Mays was born in McKees Rocks, Pennsylvania, attended Sto-Rox High School, and was raised in Pittsburgh, Pennsylvania.^[1][8] He later attended West Virginia University, where he was a walk-on linebacker on its football team during his two years there.^[9] After dropping out, he worked for his father's hazardous waste company before moving to Atlantic City, New Jersey in 1983.^[1]

Career[link]

On the Atlantic City boardwalk Mays sold the Washmatik portable washing device to passersby,^[10] along with other "As Seen on TV" products.^[1] In Atlantic City, he was taught how to sell by the older salesmen, saying "I was taught to pitch by a lot of old pitchmen. That's the kind of style I have."^[1] Mays then traveled to home shows, auto shows, and state fairs across the United States for a period of twelve years, selling various maintenance products and tools, including cleaning products and food choppers.^[10]

At a Pittsburgh home show in 1993, Mays struck up a friendship with rival salesman Max Appel, founder of Orange Glo International, a Denver-based manufacturer of cleaning products. He was then hired by the company to promote their line of cleaners, OxiClean, Orange Clean, Orange Glo, and Kaboom, on the Home Shopping Network in St. Petersburg, Florida.^[11] Customer response to Mays's sales pitches was enthusiastic, with a sharp increase in sales after his first day on the network, although some reviews were poor. He was very well known for shouting in an abrasive manner during infomercials. For example, Washington Post staff writer Frank Ahrens called him and other similar television salesmen "a full-volume pitchman, amped up like a candidate for a tranquilizer-gun takedown".^[12]

Mays was the CEO and founder of Mays Promotions, Inc., based at his home in Odessa, Florida.^[4] His services as a pitchman became highly sought-after, and he appeared in commercials for many diverse "as seen on TV" products such as Mighty Putty. Mays claimed to be an avid user of the products he promoted.^[13] In December 2008, Mays began appearing in ads for ESPN's online service, ESPN360.^[14] These ads were a slight departure for Mays as they were designed to be parodies of his and other infomercial cliches with Mays appearing to be doing a parody of himself. He also made a live appearance during the 2008 Champs Sports Bowl promoting ESPN's and ABC's January 1, 2009, bowl games.

On April 15, 2009, the Discovery Channel began airing PitchMen, a documentary series that featured Mays and Anthony Sullivan in their jobs in direct-response marketing.^[15] After Mays's death, Discovery Channel aired a special Billy Mays tribute episode of PitchMen called "Pitchman: A Tribute to Billy Mays".

On March 27, 2009, Mays appeared on The Tonight Show with Jay Leno. He and Sullivan also appeared on The Tonight Show with Conan O'Brien on June 23, 2009.^[16]

Prior to his death, Mays had signed a deal with Taco Bell to film infomercial-style commercials for the chain. Shooting was scheduled to begin in August 2009.^{[citation needed]}

Personal life[link]

Mays's first marriage to Dolores "Dee Dee" Mays ended in divorce.^[17] He had a son with Dolores named Billy Mays III, who was 22 years old at the time of Mays's death and who worked as a production assistant alongside his father on the PitchMen television show.^[18] Mays had a daughter, Elizabeth, with his second wife, Deborah Mays. His daughter was three years old at the time of his death.^[17][19] Mays's mother is Joyce Palm,^[18] and his father is Billy Mays, Sr.; they both outlived him.

In an interview during the 2008 Presidential Campaign, Mays revealed himself to be a Republican.^[20]

Death[link]

Wikinews has related news: American pitchman Billy Mays dies at age 50

Mays was found unresponsive by his wife in his Tampa, Florida, home on the morning of June 28, 2009.^[6] He was pronounced dead at 7:45 am, appearing to have died sometime overnight.^[3][7] The Associated Press reported that there were no indications that the house had been broken into, and that police did not suspect foul play.^[7] Initially, there was wrong speculation that he had a head injury after he was struck on the head by luggage after an airline landing mishap where tires blew out.^[21]

After an initial autopsy on Mays's body on June 29, Dr. Vernard Adams, the Hillsborough County, Florida medical examiner, stated that Mays suffered from hypertensive heart disease and that heart disease was the likely cause of his death. According to a toxicology report released August 7, 2009, heart disease was the "primary cause of death" and cocaine was listed as a "contributory cause of death."^[22][23] In response to the release of the toxicology report, the Mays family issued a press release stating, "We are extremely disappointed by the press release released by the Hillsborough County medical examiner's office. We believe it contains speculative conclusions that are frankly unnecessary and tend to obscure the conclusion that Billy suffered from chronic, untreated hypertension..." and said in the release that they were considering "an independent evaluation of the autopsy results".^[24]

The medical examiner "concluded that cocaine use caused or contributed to the development of his heart disease, and thereby contributed to his death," the office said in a press release. The office said Mays last used cocaine in the few days before his death but was not under the influence of the drug when he died. Hillsborough County spokeswoman Lori Hudson said nothing in the toxicology report indicated the frequency of Mays's cocaine use. Cocaine can raise the arterial blood pressure, directly cause thickening of the left wall of the ventricle and accelerate the formation of atherosclerosis in the coronary arteries, the release said. However, in October 2009, the results of a second medical examination, commissioned by Mays' family, concluded that "cocaine was not a significant contributing factor" to his death.^[25]

Longtime friend and colleague A.J. Khubani, founder and CEO of the "As Seen on TV" product company Telebrands, said Mays never exhibited any signs of drug use and was always prepared for his many commercial shoots. "I'm just shocked," Khubani said. "He was the model of a responsible citizen."

According to subsequent news reports^[26] the toxicology tests also showed levels of painkillers hydrocodone, oxycodone and tramadol, as well as anti-anxiety drugs alprazolam and diazepam. Mays had suffered hip problems and was scheduled for hip replacement surgery the day after he was found dead.

Mays's funeral was held on July 3, 2009 in his hometown of McKees Rocks, Pennsylvania. The pallbearers for the funeral wore blue shirts and khaki pants at the funeral, much like Mays wore when he advertised his products.^[27]

Fictional representation[link]

In the South Park episode "Dead Celebrities", Mays's ghost appears repeatedly to Ike Broflovski, trying to sell him products from the afterlife with his catchphrase "Hi, Billy Mays here with the...". Mays's son, Billy Mays III, a self-proclaimed South Park fan, said he loved "Dead Celebrities", and found its portrayal of his father to be both tasteful and respectful.^[28]

Notable products pitched[link]

References[link]

External links[link]

Biography portal

• Billy Mays at the Internet Movie Database
• Official Twitter page
• Billy Mays at Find a Grave