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Asked by njade to Ben, Dave, Sam, Susana on 27 Jun 2013.
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Sam Horrell answered on 26 Jun 2013:
They are sticking up to try and trap air close to your skin to make an insulating layer and keep you warm.
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Benjamin Hall answered on 26 Jun 2013:
The reason they do it is to add extra insulation when we’re cold, as the raised hairs trap a layer of air. Or, it may be an evolutinary relic that we’ve started using for a different reason. Many animals will raise their hairs when nervous to make themselves appear bigger to a potential attacker. We still get goosebumps when nervous!
The mechanism? There’s a tiny muscle at the base of each hair which contracts to erect the hair. The sympathetic nervous system (which also draws blood away from your less-essential organs, causing butterflies in your tummy) triggers the contraction.
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David Briggs answered on 26 Jun 2013:
The hairs stick up to trap air near the skin, which acts as another layer of insulation to try and keep us warm.
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Susana Teixeira answered on 27 Jun 2013:
It is the same mechanism that gives you goosebumps when you are scared or emotional (adrenalin kicks in!), and it is a defense mechanism that we inherited from our animal ancestors. Cats for example are well known for lifting their hair when they want to look scary (my labrador dog used to go all mohawk too).
Not much use nowadays when we have much less hair, and even tend to wax or shave a lot of it, but it used to trap air close to the skin to help keep our body temperature. It’s tiny muscles that lift each hair when stimulated.
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