Allergy

Name	Allergy
Caption	Hives are a common allergic symptom.
Diseasesdb	33481
Icd10
Icd9
Medlineplus	000812
Emedicinesubj	med
Emedicinetopic	1101
Meshid	D006967
Icpc2	A92

Allergy is a hypersensitivity disorder of the immune system. Allergic reactions occur to normally harmless environmental substances known as allergens; these reactions are acquired, predictable, and rapid. Strictly, allergy is one of four forms of hypersensitivity and is called type I (or immediate) hypersensitivity. It is characterized by excessive activation of certain white blood cells called mast cells and basophils by a type of antibody known as IgE, resulting in an extreme inflammatory response. Common allergic reactions include eczema, hives, hay fever, asthma attacks, food allergies, and reactions to the venom of stinging insects such as wasps and bees. Tree nuts, including pecans, pistachios, pine nuts, and walnuts, are another common allergen. Sufferers may be sensitive to one, or many, tree nuts. Typically the sensitivity is to proteins in the white, rather than the yolk.

Other foods containing allergenic proteins include soy, wheat, fish, shellfish, fruits, vegetables, spices, synthetic and natural colors, chicken, and chemical additives.

Non-food proteins

Latex can trigger an IgE-mediated cutaneous, respiratory, and systemic reaction. The prevalence of latex allergy in the general population is believed to be less than one percent. In a hospital study, one in 800 surgical patients (0.125 percent) report latex sensitivity, although the sensitivity among health care workers is higher, between seven and ten percent. Researchers attribute this higher level to the exposure of health care workers to areas with significant airborne latex allergens, such as operating rooms, intensive care units, and dental suites. These latex-rich environments may sensitize health care workers who regularly inhale allergenic proteins. Clinically, these patients often have perioral itching and local urticaria. Only occasionally have these food-induced allergies induced systemic responses. Researchers suspect that the cross-reactivity of latex with banana, avocado, kiwifruit, and chestnut probably occurs because latex proteins are structurally homologous with some plant proteins. Of these poisonous plants, sumac is the most virulent. The resulting dermatological response to the reaction between urushiol and membrane proteins includes redness, swelling, papules, vesicles, blisters, and streaking.

Estimates vary on the percentage of the population that will have an immune system response. Approximately 25 percent of the population will have a strong allergic response to urushiol. Generally, approximately 80 percent to 90 percent of adults will develop a rash if they are exposed to of purified urushiol but some people are so sensitive that it only takes a molecular trace on the skin to initiate an allergic reaction.

Genetic basis

Allergic diseases are strongly familial: identical twins are likely to have the same allergic diseases about 70% of the time; the same allergy occurs about 40% of the time in non-identical twins. Overall, boys have a higher risk of developing allergy than girls, In other words, individuals living in too sterile an environment are not exposed to enough pathogens to keep the immune system busy. Since our bodies evolved to deal with a certain level of such pathogens, when it is not exposed to this level, the immune system will attack harmless antigens and thus normally benign microbial objects—like pollen—will trigger an immune response.

The hygiene hypothesis was developed to explain the observation that hay fever and eczema, both allergic diseases, were less common in children from larger families, which were presumably exposed to more infectious agents through their siblings, than in children from families with only one child. The hygiene hypothesis has been extensively investigated by immunologists and epidemiologists and has become an important theoretical framework for the study of allergic disorders. It is used to explain the increase in allergic diseases that has been seen since industrialization, and the higher incidence of allergic diseases in more developed countries. The hygiene hypothesis has now expanded to include exposure to symbiotic bacteria and parasites as important modulators of immune system development, along with infectious agents.

Epidemiological data support the hygiene hypothesis. Studies have shown that various immunological and autoimmune diseases are much less common in the developing world than the industrialized world and that immigrants to the industrialized world from the developing world increasingly develop immunological disorders in relation to the length of time since arrival in the industrialized world.

Exposure to allergens, especially in early life, is an important risk factor for allergy. Alterations in exposure to microorganisms is another plausible explanation, at present, for the increase in atopic allergy. In particular, research suggests that allergies may coincide with the delayed establishment of gut flora in infants. It may be that the term 'parasite' could turn out to be inappropriate, and in fact a hitherto unsuspected symbiosis is at work. Vasomotor rhinitis, for example, is one of many maladies that shares symptoms with allergic rhinitis, underscoring the need for professional differential diagnosis.)||3.3 million (about 5.5% of the population) |- | Asthma ||10 million suffer from allergic asthma (about 3% of the population). The prevalence of asthma increased 75% from 1980-1994. Asthma prevalence is 39% higher in African Americans than in Europeans. Pirquet called this phenomenon "allergy" from the Ancient Greek words allos meaning "other" and ergon meaning "work". In 2006, the House of Lords convened a subcommittee that reported in 2007. It concluded likewise that allergy services were insufficient to deal with what the Lords referred to as an "allergy epidemic" and its social cost; it made several other recommendations.

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External links

American Academy of Allergy, Asthma & Immunology

Allergy & Asthma Network Mothers of Asthmatics

Category:Effects of external causes Category:Allergology Category:Immunology Category:Pulmonology Category:Immune system