Question: Why does our hair grow?

Robert Hampson answered on 11 Nov 2014:

The question “why” expects some kind of explanation which holds a meaning. I can explain how hair grows or how animals came to have hair or what hair is made from but why is a more difficult question. (Q: How did I come to have a birthday cake? It was cooked for me with eggs and butter and stuff. Why do I have a birthday cake? Because my mother loves me and wanted me to be happy on my birthday) I’ll try and explain the how as why isn’t really a question for science.

We have hair all over our body, and there are a few different types. The hair that you can find on arms and legs doesn’t really appear to grow on an adult (unless you shave it off, then it will grow back). Then beard hair for example only grows after puberty and grows thicker and more coarse than the hair on top of the head.

When hair grows there are three different stages: Anagen, Catagen, and Telogen. During anagen the hair grows quickly, during catagen the hair stops growing and the skin kind of shrinks around it to hold it in (this takes maybe a week), then during telogen, the hair remains there for maybe 100 days. Two things decide how long the hair grows, one is the length of the anagen stage (arm hairs have a very short anagen stage, head hair is alot longer), the second is how quickly cells reproduce in your hair follicles to grow the hair during anagen. Generally these cells reproduce incredibly quickly, I think they are one of the fastest in the body, but obviously some people are faster than others.

I believe head hair evolved such a long anagen phase as we lose an incredible amount of heat from our heads so we require more insulation up there. Also, hair does seem to have reproductive advantages especially for women.

Regrettably, it would be impossible to grow hair as long as Rapunzel because the hair would stop growing before it got to that kind of length.