Question: How does your hair grow?

Ciarán O'Brien answered on 20 Nov 2014:

It’s a bit like knitting, actually.

Your hair grows out of follicles, which are pits in the skin filled with cells devoted to producing the keratin that makes up hair. They work together to knit the keratin from each other into one big strand, and they don’t stop doing it, so when they knit new keratin onto the old stuff, the older stuff gets pushed out of the follicle and get’s longer.

It was probably evolution’s way of keeping animals warm, as hair is great at trapping air close to the body, forming a thin layer of insulation from the cold, and when you’re cold, tiny muscles in your skin pull at your hairs to make them stand on end, so they can trap a thicker layer of air!