The hair on your head grows indefinitely. The hair on your arms and legs grows to a certain length and then stops. You can shave it off, but it grows again, but only to that same length.
How does the hair on arms and legs 'know' how long it is?
How does the hair on arms and legs 'know' how long it is?
This was just asked and answered in /r/askscience
https://www.reddit.com/r/askscience/comments/1c6zztu/why_doe...
Different anagen phase durations.
You can observe this on many people by looking at hair miniaturization of people who have MBP or similar -- the follicle constricts in size and the resulting hair that comes out is progressively shorter in length and diameter until the follicle is so constricted that it no longer produces hair.
growth (3 to 6 years) -> static (2 to 3 months) -> fall out -> rest -> start over
The maximum length of your hair is determined by how long it stays in the growing phase, in general this phase is longer in females than in males. And some people are naturally able to grow longer hair than others.
In pregnant females the static time is increased, i.e. the hair stays there without falling out. This makes their thick and full. After delivery this changes and the hair falls out in clumps, which is unpleasant, but it's the same hair that would have anyway fallen out earlier, it's not extra hair falling out.
If you cut the hair nothing changes, it still grows for as long as it was going to originally.
That myth about cutting hair (or shaving) to make it grow faster or whatever is not real.
I've always wondered if the almost universal preference for women to have long hair is linked with their ability to have long hair, while for males people (not you :) typically want it short, which matches what males are able to naturally do.
i.e. which came first? The ability for hair of a certain length, so that's what people like, or if people like hair a certain way so natural selection helps out.
I've never experienced a time where I've trimmed body hair and had it remain the same length for a couple of months.
Look closer, the hairs are random length. You have to wait of course for them to reach natural max length, and then you'll see a randomized mix of lengths.
If you are always clipping hair they will almost all be at one length because > 90% of them are still growing and then getting trimmed. The rest (a minority) have recently fallen out and are just getting started and will be shorter.
Does that make sense?
Are you sure? I have fairly hairy body so when I use moisturizers it tends to stick to the hair instead of the skin, and since I'm trying to take care of my forearm tattoos, I trim my forearm hair on a regular basis, after a few weeks, if I look closely, I can see some hairs being around, say, 2cm long, whereas others are just barely growing out.