DSC Magazine, October 9 2022

How your body hair knows when to stop growing, and more!

body hair growth

How Does My Body Hair Know When To Stop Growing?

There’s a good reason you don’t have long, flowing locks all over your body.

It always seems weird — but extremely fortunate — that our body hair just stops growing at a certain length. It means, for example, that even if we leave our pubes unattended for several months, we can reasonably expect them not to grow halfway down to our knees. But how come?

Every hair follicle on our bodies has a growth cycle that consists of three stages. There’s the anagen phase (when the hair grows); the catagen phase (when the hair stops growing and takes a rest); and the telogen phase (when the hair falls out). After this, it cycles back to the anagen phase. 

“Different body hair has different times for each stage, hence the different lengths of hair,” explains dermatologist and trichologist David Kingsley. So despite the fact that it may appear to keep growing, scalp hair actually has a cycle that lasts about two to six years, growing about a half-inch per month. For our arms, legs, eyebrows and eyelashes, the growth phase only lasts about a month or so, then the hairs rest for a couple of weeks before falling out. The end result is that your body hair can only reach a certain length, and we all manage to avoid looking like untamed yaks.

As for why each type of hair grows to the length it does, Kingsley admits that we don’t exactly know, except to say that evolution has sorted it out. Basically, over time, natural selection has figured out that if eyebrow hair grew in front of our eyes, we wouldn’t be able to see. And more importantly, if our facial hair didn’t grow long enough, we’d never be able to rock that sweet handlebar mustache.

Pop Quiz!

When our hairs stand on end, we normally call it goose bumps. But what’s the proper scientific term for it?

A: Pilomotor Reflex
B: Horripilation
C: Piloerection
D: Duck Lumps


How Much Armpit Hair Is Too Much Armpit Hair?

Technically, there’s no reason you need to have armpit hair at all. Some scientists theorize its only purpose is to trap the body odors that emit from the armpit, a genetic legacy from our primate origins when having a strong scent was the best way to attract a mate. This, you may have noticed, is no longer the case — quite the opposite, in fact, so removing it isn’t the worst idea. But if you’re looking to trim it down rather than shave completely, leave at least half an inch, because if you cut it too short, you’ll have spiky stubble in two of the most sensitive parts of your body. And that’s the pits.

Oh FAQ: How Do I Avoid Ingrown Hairs Down There?

1. No one wants to be covered in red bumps after shaving, no matter what it is they’re shaving. Preparation is key: Soften the hairs first in a hot, steamy shower, then wash the area with an exfoliating prep scrub for a smoother shave.

2. Shave with the grain: This makes it less likely for the hairs to curl around and burrow back under the skin. Moisturize the area when you’re done, and you should enjoy real smoothness without the bumps.

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Quiz Answer

A, B & C
Turns out goose bumps have a ton of other names! They’re caused by tiny muscles at the base of the hairs, called the arrector pili muscles, contracting and pulling the hairs up. It’s thought to have been useful for our ape ancestors to fluff up their fur, either making them appear bigger, or insulating them by trapping more air, keeping them warm.