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I developed seasonal allergies when I was 33. How does my body decide that things it has encountered for decades are now hostile? by LindenSpruce in askscience

[–]Xenton 4103 points4104 points 24 (0 children)

There's a few potential causes, but I should preface this with stressing that immunology is a poorly understood and extremely variable area of medicine - meaning this answer is not going to be all encompassing and the theories presented may not be the most up to date information available.

Generally, there's two main schools of thought and they're both closely related.

  1. Sensitisation

Over time, your body learns and adapts it's immune system. If it just so happens that eventually it decides that something you've been exposed to is a threat, it will mount a response.

This response is reinforced on repeat exposures, strengthened and ultimately becomes an ongoing allergy.

Why now? Why in this form? Essentially bad luck combined with repeat exposure. Since the pollen is present often, it can be thought of as "only a matter of time" before this process occured and it happened to be now.

I dislike this theory because as much as many of the body's processes have a random element, it seems unlikely that developing an allergy could be entirely random.

Which leads to

2: Misassociation

Think scenario similar to the above, but involving a concurrent infection, virus or pathogenic substance.

Your body goes on alert after an exposure to a severe virus, it wants to make sure that whatever caused it never happens again. It just so happens that every time your body is exposed to that virus, it's also exposed to the pollen (because it's pollen season).

So your body mounts a response against both and you develop an allergy as a result. Exactly how this association gets made isn't terribly clear, but my understand is that this is the prevailing theory.

You can see good examples of this when a tick bite can trigger an allergy to red meat - even if the tick was picked up in an area with no cattle for any related proteins to be carried over.

As a sneaky third option:

  1. Your body hasn't formed a new allergy, there's just a new pollen or funghi in your area now that you hadn't been regularly exposed to before.

Maybe you moved recently, maybe there's a new weed growing. I couldn't tell you, but it's a bit of an Occam's razor solution.

Windows 10 says pins are safer than passwords how can this be when passwords have more combinations? by [deleted] in askscience

[–]8165128200 79 points80 points  (0 children)

Taken out of context, PINs are not safer than passwords. The argument that people will choose easy-to-remember passwords falls over once you start looking at dumps of PINs, where the most common ones are '0000', '1111', '1234', etc.

However, the PIN in this case isn't intended to secure an online account, which is where the real danger of weak passwords is exposed. The PIN setup is part of Microsoft Passport, which uses two-factor authentication (it identifies a familiar device plus a PIN or a biometric identification, like a picture or a fingerprint) to access your Microsoft-stored data. Microsoft is hoping that they can then start providing authentication-as-a-service, so that online services will be able to use an API to authenticate you using the two-factor Microsoft Passport authentication.

That would be a much more secure form of authentication than passwords currently are, not least because so many online services are just embarrassingly bad at handling password storage correctly, and because users have a tendency to reuse their passwords across a lot of services. So, you create an account for an order with "Jimbob's Discount Gravedigging", then Jimbob's database gets ripped off and it turns out that they stored your email address and password in plain text, and you used the same password there that you use for everything else. Now someone has access to all of your everything.

If Microsoft can successfully take over authentication for Jimbob's, then if their database gets ripped off, the attacker doesn't get anything terribly useful. If someone manages to successfully compromise Microsoft's security, they still don't get passwords that they can try using elsewhere.

edit: wow, there are a stunning number of wrong answers in this thread. I guess that's the danger of asking computer security-related questions in /r/askscience.

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Human BodyAskScience AMA Series: We've discovered that pancreatic cancer is detectable based on microbes in stool, with the potential for earlier screening in the future. AUA! (self.askscience)

submitted by AskScienceModeratorMod Bot24

Does crying actually contribute to emotional regulation? by oscarbelle in askscience

[–]StuartGotz 2503 points2504 points 2 (0 children)

Put it this way: suppression of emotions such as crying is very unhealthy. Psychologist James Gross has done a lot of good work in this area, e.g. https://pubmed.ncbi.nlm.nih.gov/12916575/. There is also a lot of research by Daniel Wegner showing a similar point: attempts to suppress thoughts and emotions tends to exacerbate them, rather than help. https://www.annualreviews.org/doi/abs/10.1146/annurev.psych.51.1.59

This is why mindfulness, cognitive reframing, and disclosure (expression via talking, writing, etc.) are healthy emotion regulation strategies. It allows for healthy ways of experiencing emotion rather than suppressing them.

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PsychologyDoes crying actually contribute to emotional regulation? (self.askscience)

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How can an almond help with digestion but also be indigestible? by GuiltyIslander in askscience

[–]DickFromRichard 130 points131 points  (0 children)

We are just starting to understand the effect of microbiome on human health, but there is a lot of interesting research going on related to this topic.

To add to this, I think it's important to note that this field of health science is really just starting to learn about the gut microbiome and practical effects and applications relating to it are really limited.

A lot of people out there will try to sell you stuff that's "good for your gut health" with no backing, typically at best it's extrapolation e.g. X was fed to a petri dish full of Y bacteria and it grew. People with ABC disease have low Y bacteria, buy my product containing X to help your Y bacteria and prevent ABC disease.

That logic is used by snake oil salesmen. If you're concerned about your gut health the best thing we really know is that diversity of micro flora seems to be a good thing and that eating fiber from a variety of sources seems to promote diversity i.e. eat your fruits and veggies and don't buy expensive unproven crap that's making big claims.

If you're really really concerned about your gut health then take pre-biotics, not pro-biotics. But the jury is still out on what effect that will really have.

How can an almond help with digestion but also be indigestible? by GuiltyIslander in askscience

[–]Cleistheknees 46 points47 points  (0 children)

None of this is true, and it blows my mind how often I see people completely making stuff up in the sub.

For almost all of our evolutionary history we had to eat a lot of low nutritional value food to survive.

Couldn’t be further from reality. The oldest hominin (A. anamensis) was a frugivore. Proconsul was a frugivore. Regardless of where you stand on the Paranthropus vs Australopithecus taxonomy, those species almost universally trend towards fruits and animal proteins, and away from the fibrous C4 plants of our more distant past. We have a lineage dominated by frugivores transitioning into the even higher nutrient-density animal foods.

So, we go from C4 plants/grasses (very distant past) to fruits, to fruits with starchy tubers and nuts, to fruits with animal foods, to cooked animal foods and cooked starchy tubers. At no point in this line are we moving down the hierarchy of nutrient density.

Our guts had to adapt to that reality.

No, they did not. The human gut is the tail end of an adaptation away from low nutrient-density foods. Even Homo erectus had a significantly smaller GI tract than it’s immediate ancestor. We have been adapting towards higher nutrient-density foods for millions of years.

Modern diets strip almost all the bulk out. This is why processed food causes so many issues like indigestion, constipation, acid reflux and even colon cancers.

This is only half of a picture. The lack of fiber itself is not a problem, and there are many indigenous groups which prove this. The problem is the refining of cereal crop carbohydrate sources. You need low fiber + high carbohydrate loads to cause problems.

Would nuclear winter reduce global warming? by CCcat44137918 in askscience

[–]CrustalTrudgerTectonics | Structural Geology | Geomorphology 47 points48 points  (0 children)

This is hard to answer definitively as there (to my knowledge) has not been an attempt to model this specifically. With that being said, the speculative answer is that a large-scale nuclear winter would likely delay the timing of projected temperature rise associated with climate change, but in as much as it would not remove greenhouse gases from the atmosphere, this represents a delay, not a "reduction" in a meaningful sense.

We can consider recent work simulating the effect of a large-scale nuclear war, specifically Coupe et al., 2019 (and an earlier paper, Robock et al., 2007 against which Coupe compare their results), which uses basically one of the same models we use to make climate change projections. The point of the Coupe paper is largely to compare the results using a newer, more sophisticated model to that of Robok et al., 2007 and demonstrate that even with a more sophisticated model, a major climatic effect is still observed (as there has been some suggestions that the extent to which there would be a "nuclear winter" was an artifact of some of the simplifications and/or assumptions in the early climate modeling in the 1980s, etc). Importantly, in both the older Robock et al model and the newer Coupe et al model, they hold CO2 concentration fixed, so this is not a direct test of how a nuclear war would influence the climate in the context of the background of anthropogenic climate change. What the newer Coupe et al paper finds is a rapid and drastic drop in global temperatures and major changes in precipitation patterns as well, which together would have catastrophic effects on agriculture basically everywhere on Earth. Relevant to the question at hand, the recent modelling suggests that the duration of this global temperature change would be around 10 years, i.e., after 10 years, the average temperature would return to close to the baseline in the model. This does depend a lot on the forcing, i.e., how they are simulating the result of nuclear war, i.e., the injection of "black carbon" (soot) from the burning of cities, etc into the upper atmosphere. The magnitude and duration of cooling depends on the amount and height injection of the black carbon, which is hard to constrain.

Now, turning our attention to more traditional anthropogenic climate change, the critical thing to realize here is that changes occur slowly and are lagged. This means that the warming we are experiencing now is the result of the integrated emissions history of the past and even if we stopped emitting today (or even if we stopped emitting today and started removing CO2 from the atmosphere) warming would continue for decades. From an extremely (and I do emphasize extremely) oversimplified perspective, we could consider this in the context of an idealized greenhouse model, which essentially says there is an equilibrium temperature for a given capacity for the atmosphere to absorb of heat (what the CO2 and other greenhouse gases are doing). That equilibrium temperature is not reached instantaneously, i.e., if we held CO2 concentration fixed in the atmosphere, the atmosphere would keep warming until it reached the new equilibrium (again, super super simplified, ignoring tons of complications, feed backs, etc, - this is just for simple explanation purposes). In less idealized models of the climate response to different emissions / behavior scenarios (e.g., SSPs) we can see this lag, i.e., if we look at projections for the future in figure 4.2 on page 155 of the latest IPCC report (warning BIG pdf) we can see even for scenarios with a reduction in concentration of CO2 (e.g., SSP1-1.9), warming continues for a while after the reduction starts. This is all to say, that even if there was a hypothetical massive, but ultimately short lived, reduction in temperature from something like a global nuclear war, after the end of this "anomaly", if a reduction in CO2 and other greenhouse gases had not occurred in the interim, then you'd basically expect global warming to "pick up" where it left off.

Of course, the above is very hypothetical and extremely oversimplified because the atmosphere is incredibly complex and without direct modelling, it's hard to know whether you would expect interactions between the two sets of processes leading to other behaviors. Hypothetically, the result of a global nuclear war, i.e., destruction much of the worlds infrastructure and resulting widespread famine from the collapse of most agriculture in turn reducing the worlds population further, would result in a pretty dramatic reduction in anthropogenic greenhouse gas emissions. As above though, if concentration of the greenhouse gasses did not reduce (and simply held steady after most everyone was dead), the expectation would be continued warming to the new equilibrium for the concentration of CO2 (after recovery from the nuclear winter).

In summary, nuclear winter represents a mechanism by which to reduce global warming in the same way that killing a patient represents an effective way to stop an infection. Beyond that, without direct simulation it's hard to know definitively, but it's reasonable to think that nuclear winter would not reduce global warming, but only delay it, unless you were comparing the cases of "no nuclear war, but continued wholesale burning of fossil fuels" vs "nuclear war and near extinction of the species and a lot less burning of fossil fuels", then on long-time scales (after the recovery from the nuclear winter), yes, the latter case would probably see a "reduction" in global warming compared to the former case.

Do animals benefit from cooked food the same way we do? by Rusk- in askscience

[–]CromulentInPDX 10 points11 points  (0 children)

I just read an article (because I wasn't convinced by their claim that it's clear they didn't start fires) and it was about marks on flint tools called bifaces. They would have used them to start fires. An anthropologist was able to start fires using those he created and found the markings were similar to historical versions.

They quote another scientist that isn't convinced, but admits the historical record is sparse, because in caves that have been examined they found evidence of fires in warmer periods (when lightning is more likely), but not colder periods.

Here's the link if you're interested, it was a very quick read:

https://www.theatlantic.com/science/archive/2018/07/neanderthals-fire-mystery/565514/

Can someone exaplain the new covid brain damage study? by Striking-Hall1705 in askscience

[–]IJumpYouJumpJack 4246 points4247 points 2 (0 children)

Basically they looked at 401 people who had imaging done before and after they got COVID and compared it to 384 people who did not have covid. The 3 main results they found are:

  1. less brain matter in the orbitofrontal cortex (responsible for higher cognitive abilities like impulse control) and the parahippocampal gyrus (area associated with memory)
  2. tissue damage in areas connected to your sense of smell
  3. reduction in brain size

The overall reduction in brain size has a mean difference of 2%. Whether this is small or large is sort of subjective based on what you consider "small or large" but it does lead to cognitive decline compared to the control group. They do not know if this change is permanent, they'd need to follow the patients longer to know. Since the age of this population is 51-81, it's hard to tell whether these results extrapolate to younger populations without studying them also.

​

Edit: Since people have been asking, thought I'd also add that the paper did not look into vaccination status or severity of illness. They did account for hospitalizations, but there were only 15 hospitalizations out of the 401 covid participants.

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COVID-19Can someone exaplain the new covid brain damage study? (self.askscience)

submitted by Striking-Hall1705

Why does a can of compressed air get ice cold when used? by WodensEye in askscience

[–]ChemomechanicsMaterials Science | Microfabrication 18 points19 points  (0 children)

First, cans of "compressed air" contain a liquid that boils, providing a lot of gas and a lot of incidental cooling. PV=nRT doesn't apply to a liquid.

But if the container contained only compressed gas (like a SCUBA tank), then letting that gas expand would decrease the temperature, yes. P would decrease, V would increase, and T would decrease. This can be modeled as an adiabatic expansion where, as you note, the pressure decreases more than the volume increases, resulting in decreasing temperature. Another way to look at it is that the compressed gas is doing work pushing the atmosphere out of the way, and so its internal energy—and its temperature—must decrease.

CPUs carry out anywhere from 1 to 32 instructions per clock cycle; if so few instructions per clock cycle are being performed, what is the benefit to cramming billions of transistors onto one chip? by perigee392 in askscience

[–]symmetry81 1226 points1227 points 2 (0 children)

A single transistor doesn't really allow you to do much, at most to take two bits and barely perform an AND or OR operation on them and only then if you're willing to throw in a resistor as well. Lets say that you want to do somthing more complicated like add two 32 bit numbers. The most transistor efficient way to do that without also adding resistors will take 16 transistors per bit or 512 transistors total.

But you don't want a computer that only adds numbers. You want a wide variety of instructions you can execute, you want some way of choosing what instruction you execute next, and you want to interact with memory. At this point you're up to 10,000s of transistors. That will give you a computer chip with the sort of performance you would have seen in the 1970s but with somewhat faster clock speeds because of our improved ability to work with silicon.

Now lets say you don't want your entire operating system to crash when there is a bug in any program that you run. This involves more transistors. And you probably want to be able to start one multi-cycle instruction before that last one finishes (pipelining). This might get you up to executing one instruction every other clock cycle on average. That'll cost transistors as well. This will grow your chip up to 100,000s of transistors and will give you performance like the Intel 386 form the mid 80s.

But this will still seem very slow compared to the computers we use nowadays. You want to be able to execute more than one instruction at a time. Doing that isn't very hard but figuring out which instructions can be executed in parallel and still give you the right result is actually very hard and takes a lot of transistors to do well. This is what we call out of order execution like what the first Intel Pentium Pro had in the mid 90s and it will take about 10 million transistors in total.

But now the size of the pool of memory that we're working with is getting bigger and bigger. Most people these days have gigabytes of memory in their computers. The bigger the pool is the longer it takes to grab any arbitrary byte from it. So what we do is have a series of pools, a very fast 10kB one, a slightly slower 100kB, a big 10MB one on the chip, and then finally your 8GB of main memory. And we have the chip figure out what data to put where so that the most of the time when we go to look for some data it's in the nearby small pool and doesn't take very long to get and we're only waiting to hear back from main memory occasionally. This and growing the structures that look forward for more instruction to execute are how computers changed until the mid 2000s. Also going from 32 to 64 bits so that they could refer to more than 4GB of memory, the biggest number you can say in only 32 bits is 4294967296 so any memory location over that number couldn't be used by a 32 bit computer. This'll get us up to 100 million transistors.

And from the mid 2000s to the mid 2010s we've made the structures that figure out which instructions to execute next even bigger and more complicated letting us execute even more instructions at once. As we grow performance this way the number of transistors we needs grows as the square of the performance, on average. And we've added more cores on the same chips letting us grow performance linearly with transistors as long as software people can figure out ways to actually use all the cores. And now we're up to billions of transistors.

EDIT: Clarified TTL versus RTL.

EDIT2: Here's a block level diagram of a modern core. You can see even at that level just how complex it is.

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Earth SciencesWhat was Earth like in the 1000 years after the K-T extinction event? (self.askscience)

submitted by pretende

Why does the Hawaiian underwater mountain chain make a huge turn? by The_ArcReactor in askscience

[–]CrustalTrudgerTectonics | Structural Geology | Geomorphology 713 points714 points 3222& 3 more (0 children)

Why does it make such a turn? Was it the hotspot or the plate?

Both...maybe. The classic interpretation of the large bend in the Hawaiian-Emperor Seamount Chain is that the location of the hotspot generating the islands and seamounts is fixed with respect to the center of the Earth (e.g., Morgan, 1971) and that the bend reflects a change in Pacific plate motion (e.g., Morgan, 1972a, Morgan, 1972b). If you've taken an introductory geology class, this is probably the explanation you've gotten for this bend and in general, is discussed in the context of hotspots being a fixed reference frame to which we can reference plate motions. However, there have been major issues with this simple explanation for decades, which has led some to suggest that the bend results from movement of the hotspot, not a change in the direction of the Pacific plate (e.g., Norton, 1995).

At present, it's pretty well accepted that the old idea of fixed hotspots is not correct, i.e., they do drift. However, the extent to which hotspot drift vs a change in plate motion causes the bend in the Hawaiian-Emperor chain largely remains unclear. Torsvik et al., 2017 essentially argues that a combination of a true change in plate motion and hotspot drift are necessary to explain the bend. Alternatively, Bono et al., 2019 instead suggest that no change in Pacific plate motion is required and that the bend is completely caused by hotspot drift. More broadly, Wessel & Conrad, 2019 describe how depending on the assumptions for plate motions and other details (e.g., how true polar wander do you allow to occur in your model) you can get scenarios where the bend is caused by a change in plate velocity or where the bend is caused by motion of the hotspot to work, i.e., it's largely a problematically underconstrained problem.

Do such big shifts in direction happen often?

Independent of the particular questions regarding the bend in the Hawaiian-Emperor seamount, global plate reorganizations, i.e., geologically rapid changes in the direction and magnitude of the velocity of multiple tectonics plates, absolutely do happen. In fact, one of the original problems with attributing the bend in question to a change in plate motion, as described by Norton, was the lack of a global plate reorganization at the time of the formation of the bend (though with both better dating of the timing of the bend and consideration of some of the details described in previously referenced papers, there is arguably a reorganization that might be associated with the bend). In other geologic periods, there are less ambiguous lines of evidence for global plate reorganizations. In general, things like the initiation of mantle plumes or large-scale collisions (e.g., like the collision between India and Eurasia forming the Himalaya) are events thought to be able to initiate global plate reorganizations (e.g., Muller et al., 2016, Olierook et al., 2020). In a paper coincidentally published today, Gurer et al., 2022 nicely demonstrate how a change in the interaction of two plates (e.g., through the initiation of a plume) can cascade into a larger plate reorganization. In terms of the frequency or regularity of these global plate reorganizations, that's a bit harder to answer. They are not uncommon in the geologic record, but are also not always happening or periodic.

Do NSAIDs help soft tissue injuries heal? by Rumple28 in askscience

[–]mathrufker 1549 points1550 points 42 (0 children)

Top answer is misinformed. First and foremost, nsaids are not linked to injury through swelling by “bleeding.” when nsaids are linked to greater injury the mechanisms are super complicated because inflammation is super complicated. It typically involves misbehavior of specific group of cells, not bleeding.

The answer to your question is its still unclear. Studies and meta analyses are super mixed. There are studies showing high dose nsaids post surgery help but long term is bad, and there are studies in animals showing acute nsaid use is bad and late phase healing they’re good. What we do know, flat out, is that certain subtypes of inflammation lead to scarring and improper cell regeneration which NSAIDS can help fix but also that NSAIDS can interfere in healing through other mechanisms not completely understood

Overall clinical consensus is that pain management, especially in physical injury, encourages early mobility which is usually better than sitting on ur ass. The classic treatment of ibuprofen and cold therapy is not completely based in science

Source: I study inflammation and endothelial repair

Edit: People are asking about how to reduce inflammation. the number one source of inflammation in the modern world is being overweight. Don’t be overweight, exercise outdoors and eat leafy greens. I cannot overstate how powerful these life practices are.

Edit 2: exercise outdoors so you get exercise + vitamin d and lower stress. The outdoors and all its microbes are fucking magical for our immune system. Just try to avoid bird shit and bat ridden caves lol they nasty (from an immunology perspective)

Why are earth’s natural resources seemingly not evenly distributed across the planet? by GuitarProJon in askscience

[–]CrustalTrudgerTectonics | Structural Geology | Geomorphology 27 points28 points  (0 children)

For the majority of metals and ores, and to a certain extent the majority of mineral resources, it's important to realize that there are multitudes of segregation processes operating on a variety of scales. This is already well addressed in one of our FAQ entries.

For petroleum and coal, these both represent deposits formed in areas (and during times) of abundant, predominantly photosynthetic, biomass. Thus, the reason for localization of these deposits is simply that the environments capable of generating these deposits were/are not globally uniform. The correct mental model would be essentially areas where there was extremely dense biomass production and relatively high sedimentation rates (perhaps with favorable chemical conditions as well, i.e., anoxic) and finally a particular burial history (i.e., to get the biomass hot enough to form the relevant material, but not so hot as to destroy them).

For coal, modern day swamps are in many ways similar to the coal swamps of the Mississippian and Pennsylvanian periods that produced much of the worlds coal, the primary difference being the scale, i.e., Carboniferous swamps covered huge portions of land (and to head off anyone with the "but coal formed during the Carboniferous because there weren't organisms capable of decomposing lignin yet" quip, this idea largely based on Robinson, 1990 is demonstrably false, e.g., Nelsen et al., 2016).

For petroleum, the source of the biomass is largely phytoplankton, e.g., diatoms, etc. So areas with high rates of primary productivity in the oceans or large lake systems and high sedimentation rates (e.g., near shore environments, etc) represent the right conditions to form petroleum.

Ask Anything Wednesday - Physics, Astronomy, Earth and Planetary Science by AutoModerator in askscience

[–]mfb-Particle Physics | High-Energy Physics 1 point2 points  (0 children)

Area/volume matters

The pressure washer pressure is the value close to the nozzle, in a very small area designed to withstand a high pressure. The pressure at the target will be lower.

The overpressure from nuclear weapons is a rapid change in pressure over a huge area, measured kilometers away from the explosion.

  • If you would aim a million pressure washers at a building you would destroy it, too.
  • If you measure the pressure inside the exploding nuclear weapon you get far higher values.

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EngineeringAskScience AMA Series: Molecular engineering (MolE) encompasses everything from protein design, nanomaterials, vaccine development, battery/solar cell design, & much more. We're a group of students, professors & staff connected to the University of Washington's MolE Institute. AUA about MolE! (self.askscience)

submitted by AskScienceModeratorMod Bot322

What does the "BA" stand for when talking about omicron variants? by landoncolby in askscience

[–]SpeakerToLampposts 342 points343 points  (0 children)

These are from the PANGO lineage designation system (https://www.pango.network). They're based on the inferred phylogeny (i.e. family tree) of the various variants. Variant B.1.1.529 (aka Omicron) is descended from B.1.1, which is descended from B.1, which is descended from B (which is the first haplotype that was detected). More specifically, B.1.1.529 is the 529th descendant of B.1.1 that the pango group have assigned a number to.

So what about "BA"? To keep these sequences from getting too long, they assign aliases, and BA is the alias of B.1.1.529 (they ran out of single-letter prefixes a while ago). So BA.1 is short for B.1.1.529.1, and BA.2 is short for B.1.1.529.2, etc. (And since these are all in the Omicron family tree, they're all classed as Omicron subvariants.) Similarly, the original Delta variant was B.1.617.2, which was assigned the alias AY, so AY.1 (=B.1.617.2.1), AY.2 (=B.1.617.2.2), etc are all Delta subvariants.

The current full lineage list is available at https://cov-lineages.org/lineage_list.html. Note that they're tracking variants in far more detail than any non-virus-nerd cares about. If I'm counting right, there are 1634 non-withdrawn lineages listed, including 41 in the Omicron family and 233 in the Delta family.

Why does hair itch when growing back, and why does scratching it make it itch more? by milpool90 in askscience

[–]pandapoi 24 points25 points 2 (0 children)

A thin layer of skin does not grow over the follicle.

The idea is right, though. The irritation OP is getting is normal, but can be significantly reduced by proper shaving. It's also likely caused by ingrown hairs that never actually become ingrown, like razor bumps.

The mechanics are as follows: When you shave, you are cutting the hair cleanly on an angle parallel to the surface of the skin. However, the hair being cut rarely, if ever, grows perpendicular to that angle. More typically, the hair grows at a slight downward angle. So you end up cutting this \ straight across, and one side ends up sharper than the other. This is especially a problem with androgenic hair, like on your legs, which is thicker and coarse. It's like sharpening thousands of little knives. When the hair begins to grow back, it grows in its typical direction, which will often cause that sharp end to poke at the side of the follicle. Your body recognizes this small trauma and sends an immune response, which in turn results in localized inflammation at the site of the hair follicle. This is uncomfortable.

However, this can all be avoided. Consider that you are probably shaving with a multi-blade razor, and it might even have one of those little rubber bits endwise that pick the hair up. In the context of shaving problems, this can be BAD. You know those commercials where they show a macro of the hair being shaved? First the little rubber part picks up the hair. It holds it up so the first blade can cut it. Then two or three subsequent blades cut the hair right after, while the former blade is still holding it up. The end result is that the hair is redirected out of its natural growth pattern before it is cut. Just like in the macro, after it's cut, it is released and falls down below skin level.

So now you have a really sharp piece of hair resting below the surface of your skin trying to grow at an angle. And that type of hair naturally curls, too. Your hair is stabbing you from the inside out. This problem is especially common in black people, whose hair is naturally thicker and curlier

Now here's how to minimize this completely: shave correctly. This is important information for any adult, male of female, and should be used when shaving anywhere on your body.

First, use a sharp razor. If you're shaving your legs with it, you wont get many uses out of a single razor. Second, shave with something meant for shaving. Don't use soap, as it'll dry your skin. Don't use conditioner because I said so. Wash your body first. The hot water will soften the hair and make it easier to cut, which is good for your skin and good for the razor. Before you shave, exfoliate the area. You don't have to use a belt sander, just make sure you get your scrub on to fully expose the hair for a clean cut. Sometimes I cry in the bathtub because I'm so alone. Lather up your shaving cream, apply it and leave it there for a minute or two. It's designed to soften the hair and lubricate the skin and razor. Most important, use a SINGLE blade razor. Use a maximum of two if you absolutely have to. Passing a blade along your skin is irritating to begin with, but four or five just kills it. With a single blade razor, you end up with a clean shave and smooth skin with little risk of razor bumps or ingrown hairs. Fun fact: Razor bumps are mostly due to the irritation of the razor scraping the skin and the hair poking at the follicle. Ingrown hairs occur when the hair turns around on itself before it can exit the follicle's opening, then just keeps looping and growing. They can also be caused by anything else that might block the follicle (clogged pores from over-active sebaceous glands, etc.). The easy way to deal with these is to get a needle-point pair of forceps or tweezers and kind of pick the hair out and extract it from the follicle.

You only need one or two passes over each area of skin. If you can still feel the stubble after that, you need to get a new blade on your razor.

After you shave, rinse the area off well with cooler water than you just bathed with. Towel off, and immediately apply moisturizer and some kind of astringent. On your face, use something labelled as non-comedogenic. Something basic, too. Moisturizing your skin keeps it pliable so the deadly knife waiting below your skin can easily clear the surface and grow properly. The astringent is just good practice to normalize the ph of your skin, which should be slightly acidic. Apply these while your skin is still not completely dry, as the moisturizer will tend to lock the moisture into your skin and prevent dryness for a longer period of time. A healthy skin care regimen will help a lot, too, and it doesn't just have to be for your face. You can also use depilatory creams and waxing instead of shaving. These help.

This comment wasn't really meant to be this long. I suppose I just had a lot of pent-up shaving rage that I needed to get out. The reason I know these things is because I spent an unfortunate part of my life studying skin care at length. As a result, I have enforced strict personal grooming policies with all of my partners. In the case of non-compliance, I have actually shaved them myself. This is true. Thank you for reading everything I have to say about shaving. It really means a lot to me.

tldr; The act of shaving is both an art and a science. When executed by a skilled professional, it can be a unique and rewarding experience. Careful preparation and deliberate methodology is required, however, as a reckless shave can lead to a life of woe.

Since the sun's upper atmosphere is hotter than the surface, and we've already sent spacecraft through the upper atmosphere - what is stopping us from sending a spacecraft close to the surface of the sun? by epsilonal in askscience

[–]graebot 2817 points2818 points 233 (0 children)

"Hotter" is confusing in this context. Temperature and heat are different things. Sun's upper atmosphere has a much higher temperature, but much, much lower pressure / density than the surface. So upper atmosphere has much less heat than the surface, even if the particle temperature is higher. In terms of a spacecraft surviving the heat, it depends how hot the spacecraft materials will get. It won't be anywhere near the temperature of the upper atmosphere, because all the atoms on the craft surface is continously radiating heat. And the hotter the surface the more heat is radiated. The atoms in the upper atmosphere are very sparse, so even though a very hot atom hits your craft, does some local damage to the surface maybe kicks a few atoms off into space, the local temperature quickly dissipates amongst the other surface atoms. Your craft surface would stay relatively cool, but slowly get eaten away by the solar wind over time, in the upper atmosphere. Near the surface however, the heat is extreme, even though the temperature is lower. So many particles are hitting the craft surface, transferring heat, and the surface can't radiate it away quick enough. The crafts surface quickly heats up and melts, losing all integrity

What would the horizon look like if you were standing on an infinitely stretching and perfectly flat plane? by AhrmiintheUnseen in askscience

[–]MidtekApplied Mathematics 4333 points4334 points  (0 children)

Actually, the question "where is the horizon?" and "what does the horizon look like?" are different questions. Let's answer the first question.

Where is the horizon?

How do you find the horizon anyway? Suppose you are on a spherical object (like Earth). Here is a picture to make things clear. The variables are

  • R = radius of Earth

  • H = height of vantage point (e.g., distance from your eyes to the ground)

  • θ = viewing angle (i.e., the declination angle at which you see the horizon)

The farthest point you can see is the point where a line passing through your eyes is tangent to the circular cross-section of Earth. From the diagram, some simple trig shows that your viewing angle is

θ = cos-1[ R/(R+H) ]

With H = 6 feet, we get θ = 0.043 degrees.

What is your viewing angle for an infinite plane? Well, go back to the picture of Earth. Can the viewing angle be any positive angle? Nope. If you look exactly parallel to the plane, then your line of sight does not end on the plane. But as soon as you look down at even the slightest angle, your line of sight meets the plane. So your viewing angle on an infinite plane is always 0 degrees, no matter how high your vantage point is. So if Earth were an infinite flat plane, for instance, the horizon would be pretty much exactly in the same place where it is now (at least for low vantage points). The angle 0.043 degrees is imperceptibly close to 0.

What does the horizon look like?

Okay, so what would the horizon look like? For this, we need some physics. For reasons that will become clear, let's also assume that there are no other planets, no other stars, etc. The universe is just this infinite plane of uniform density (and you, I suppose).

An infinite plane with a constant mass density has a very simple gravitational field. It is uniform on each side of the plane, no matter how far you are from the plane. So if you are right on the surface of the plane, you measure some gravitational acceleration g. If you go up a height H, you measure the same acceleration. It is a completely uniform field (on each side) that always points towards perpendicularly toward the plane.

So what? What does this mean? Well, the path of light gets bent by gravity. Even the path of light passing by Earth gets bent, by a very small amount. (Deflection of light by the Sun is a classical test of general relativity.) The same happens for an infinite plane, but the difference now is that it has all the time in the world (or I suppose, distance) to deflect right back to the plane itself. Here is another picture. Light emitted from the plane will eventually curve back to the plane. Yes, it takes a very large distance for this to happen for, say, a gravitational field as strong as Earth's gravity, but that's fine: the plane is infinite. When the light finally is received, it is received at some angle. Our brain always perceives light to have traveled a straight line. So even though the light path is curved, we will perceive the light to have come in from some point in the sky.

Ultimately, this means that the entire sky is entirely filled with images of the surface of the plane some distance away. (This is why I assumed there were no other planets, stars, etc. so that light rays do not get obstructed.) In other words, it looks as if the entire world has curved up around you and closed at the top. So it looks like you are actually in some very large spherical planet, for which the "surface" is the interior of the sphere. But remember that images above you are really emitted from points on the plane very far away. (The point directly above you is infinitely far away.) So as you walk in a straight line on the plane, you won't really see the entire sky rotating around to meet you like you would expect if you were inside a spherical planet. For instance, the point directly above you never appears to move. Try as you might, you will never reach the point where the image directly above you was emitted.

By the way, what does the point directly above you look like? Well, it's where all the points infinitely far away from you are sent by ray-tracing all of the light back. But points infinitely far from you in this world make up the horizon! So instead of seeing the horizon exactly where it is now on Earth, you would see the horizon directly above you all crunched up into a single point.

edit: A few people have (falsely) noted that a 45-degree launch angle maximizes horizontal range and that all the photons start with the same speed. So you end up only seeing some finite portion of the plane around you. This is not correct. That line of reasoning treats light as a ballistic particle in a Newtonian uniform gravitational field. Light cannot be treated in Newtonian gravity: it is neither affected by nor affects gravity in the Newtonian framework. For one clear difference, note that the light paths in a uniform field are not parabolas; they are actually semicircular arcs.

Also, the oft-repeated statement "the speed of light is constant" is simply not true in GR if you take it at face value. The speed of a light signal next to you is always c, sure. But the local speed of light for distant light rays, in general, depends on the coordinates. This is not a contradiction; it is an artifact of the freedom of choosing coordinates in GR.

edit 2: I have to admit that I have committed a cardinal sin that I absolutely hate to see committed by others: indulging hypotheticals that are sort-of unanswerable.

If we do everything in a Newtonian framework, then the first part of my response is just fine. The horizon is at 0 degrees, which is barely less than the Earth horizon at about 0.043 degrees for the height of a typical person. For the second part of my response, I did two things:

  • used Newtonian gravity to deduce that the gravitational field of the plane is uniform

  • used GR to determine the paths of light rays in a uniform field

(Now, technically speaking, there is no metric in GR that has all of the desired properties of a uniform field from Newtonian gravity. There are several candidates though. I just used the simplest of them, which is Rindler coordinates for flat spacetime. But that is a small technicality that doesn't matter too much.)

There really is no metric that describes an infinite plane of uniform density, at least not one that I can think of or calculate. Perhaps there are some good GR models of such a matter distribution. Anyway, my error of combining the two frameworks of gravity was subtle, but important enough to point out. So take what I said about what the horizon looks like and light deflecting back to you with a grain of salt. There are some unphysical assumptions that go into that.

Better... just assume that the infinite plane of uniform density is not there. Assume space is just a vacuum, but there is a uniform gravitational field nevertheless. (You can have non-trivial metrics even in a vacuum, e.g., black hole, so this is not a contradictory statement.) If the field is in the z-direction, then we can talk about what happens to light emitted at points on the plane z = 0. That is a more physical problem that can actually be answered in GR somewhat. Just don't think too hard about how we could produce such a uniform field with matter.

edit 3: With the second edit above in mind, see this post for my thoughts on concerns about my not taking into account any atmosphere.

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BiologyDo other animals perceive taste like we do (Sweet, spicy, salty, bitter, sour and umami)? (self.askscience)

submitted by CrappysaurusRex

Why does the immune system specifically attack the joints in rheumatoid arthritis? by TrueAbbreviations491 in askscience

[–]EmergenceRxn 1588 points1589 points 3 (0 children)

Hi there! Different parts of the body are made of different materials (different proteins, connective tissues, etc.) Each material can have a specific sequence (antigen) that the immune system recognizes, and most of the time it just says “ok that’s a normal part of our body, leave it alone.” In autoimmune diseases the immune system mistakenly recognizes one of these antigens as foreign and attacks it. In RA those antigens are in the joints. In IBD the recognized antigens are in the bowels, in MS those antigens are in the brain. I hope this helps!

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