What causes hairs to curl after reaching a certain length?
March 6, 2016 5:35 AM Subscribe
My friend's son's hair starts getting curly after it grows a few inches long. What would cause hair to switch from being straight to being curly after growing a certain length (or, probably more accurately, after a certain amount has passed since a certain point on the hair was created)?
i don't understand the details of this paper, but i think the transition from 2D to 3D shapes that they identify may be relevant. if so, my rough guess at what they are saying is something like:
posted by andrewcooke at 8:04 AM on March 6, 2016 [1 favorite]
for shorter lengths, the hair curves in a simple way (like an arc of a circle, drawn on paper). but once it gets past some critical length it starts to spiral, like a corkscrew.and if that's right, then it may explain what you see. when shorter, all each hair wants to do is bend in one direction or another. because there are lots of hairs, laying against each other, they stay flat. but once they grow longer they start to spiral, and that gives them volume, and then they bunch up in spirals, and then you've got visible curls.
posted by andrewcooke at 8:04 AM on March 6, 2016 [1 favorite]
(the paper doesn't really explain why there's a change from curves to spirals as hair gets longer. it seems to just come out of the maths. so i don't have a "deep" explanation, sorry.)
posted by andrewcooke at 8:12 AM on March 6, 2016 [1 favorite]
posted by andrewcooke at 8:12 AM on March 6, 2016 [1 favorite]
Well, think about a shallow curve. What happens as it gets longer? Eventually it loops back on itself.
But the original shallow curve, if you drew that over and over on someone's head, it looks pretty straight. It might be wavy when it's wet, and it might have a little more volume when it's dry (but if we're talking very-little-kid baby-fine hair, that has almost no volume anyway), but until it gets long enough for that curve to coil it's difficult to see.
If it's a tight curl, you'll see that full loop expressed in a shorter strand of hair (as a white person example: Justin Timberlake) than those of us with looser/bigger curls. My curls are so loose and my hair is just fine enough (especially at the crown and front of my head; the back of my head is a tighter curl) that it really takes a good 6 inches of length before the pattern repeats enough to sustain itself. Before that, I go through stages of increasing unruliness, despair, product, and flatirons until it grows long enough.
posted by Lyn Never at 8:35 AM on March 6, 2016 [2 favorites]
But the original shallow curve, if you drew that over and over on someone's head, it looks pretty straight. It might be wavy when it's wet, and it might have a little more volume when it's dry (but if we're talking very-little-kid baby-fine hair, that has almost no volume anyway), but until it gets long enough for that curve to coil it's difficult to see.
If it's a tight curl, you'll see that full loop expressed in a shorter strand of hair (as a white person example: Justin Timberlake) than those of us with looser/bigger curls. My curls are so loose and my hair is just fine enough (especially at the crown and front of my head; the back of my head is a tighter curl) that it really takes a good 6 inches of length before the pattern repeats enough to sustain itself. Before that, I go through stages of increasing unruliness, despair, product, and flatirons until it grows long enough.
posted by Lyn Never at 8:35 AM on March 6, 2016 [2 favorites]
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posted by Swisstine at 7:06 AM on March 6, 2016 [2 favorites]