Why doesn't the hair on our eyebrows or eyelashes continue to grow?

Question

Yet hair everywhere else grows contantly

Answer 1

Each hair you have grows out of a follicle. Hair follicles have a cycle of resting and growing that goes like this:
1. Rest: follicle has no hair growing in it.
2. Growth: the hair starts to grow and continues for a length of time. The length of the hair reflects how long it has been growing, and the hair follicles from different parts of your body have different pre-programmed amounts of time that they will grow. So, for places with short hair, like eyelashes, the time for growing is short. For the hair on your head, however, the follicles grow for years.
3. Rest: Once the growth period ends, the hair stays in the follicle for a while.
4. Shedding: Eventually, the bottom of the hair loses its connection with the skin, and the hair falls out.

After the hair falls out, the follicle goes back to step one and starts over. The cycle can eventually be disabled by the male sex hormone, testosterone, in the follicles of your scalp, and so many men (and some women) go bald as they age.

This whole cycle happens in all mammals for all their hairs and fur. The only real natural exception is in humans for the hair on our scalps: this hair really seems to grow much longer than is necessary, and so we have to cut it all our lives or find ourselves unable to see. (Horse tails are long, but they have a use, and animals like sheep or sheep dogs have been bred artificially to have long hair.)

So I think the real question should be why the hair on our heads grows so long when all other natural hair in the world only grows to a useful limit?

Answer 2

1

Answer 3

All hair grows continually. The reason some hairs are shorter is because they fall out naturally earlier than hair on our heads. So an eyelash (yes it is a hair!)will come to the end of it's life at 7mm or something, a leg hair maybe 2cm.
The reason it happens is because if they kept growing forever, we'd have a big curtain in front of our eyes, and not be able to see. So of people with short lashes are favoured in evolution.
Lots of people trim their eyebrows to keep them tidy because they get too long (and no, there is no evidence this makes them grow faster, hair doesn't know when it has been cut, it has no nerves or sensors)

Answer 4

All hair has a natural length. Eyelashes are short, head-hair is longer, but the length varies from person to person.
Once your hair has reached its length, it will never grow any longer no matter how long you wait.
Be thankful that eyebrows don't keep pace with head hair, life on a deserted beach could become hazey in quite a short time!

Answer 5

Please take notice from an old fossil. It does grow.
My eyebrows look like I'm a puppet from the thunderbirds. eyelashes fall out after a time and are replaced by ones that are growing, it just seems like they are not growing but they are.

Answer 6

We all know it does grow, but we all know what you mean.
It's just the way our bodies are designed, the eyebrows & lashes protect our eyes from things that would otherwise blow or drip into them. They wouldn't be very convenient if they grew to long because we wouldn't be able to see, so our natural defences stunt their growth, as with our pubic nasal and ear hair, for other obvious reasons.

Answer 7

well only the hair on our head keeps on and on growing. on the rest of our body hair grows but only to a limited length..we cud not grow the hair even on our arms and legs as long as the hair on our head. so y only single out eyelashes and eyebrows...if we shave them off they will grow back to the same length again like the hair on our arms or legs or underarms. the hair on our head grows much longer because of the blood circulation being most in that region...whereas it is limited in other parts of the body.

Answer 8

Because body hair, facial hair, pubic hair, all have a different life expectancy. Asian hair stays live for roughly 7 years however, European hair lives for 3-4 years. Eyebrows and lashes live for about 6 weeks.

Answer 9

Eye lashes only need to grow long enough to protect the eyes from dust and dirt, the eye brows do grow longer on older men, but generally stay short as you would not be able to see with hairy eye brows!!

Answer 10

I am not sure but I thought they did continue to grow. I have seen some really scary old man eyebrows at work. Ewww and ear hair!!!