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Hair, hair, everywhere!

Teenage boys get facial hair

Not only do you gain your first pubes, but your whole body becomes more hairy when you're a teenager.

Firstly, hair on the arms and legs becomes more noticeable. Next, pubic hair starts to grow around the groin and under the arms. Finally, boys grow hair on the chest and sometimes the back and they start to grow a beard. Teenagers want to grow this hair at the same time as everybody else. It can be difficult to be the one who has the earliest hairy armpits, or the latest.

Pubic hair

Pubic hair is quite different from hair on the head. Instead of forming a round shape, the hair is oval. It is always short and has a coarse and curly texture. The growth period for pubic hair is short. Within six months, the hair follicle dies and the hair falls out. Pubic hair never gets a chance to grow longer.

Watch pubic hair sprouting at puberty. You will need Flash Player, it for free.

It is not certain why pubic hair grows in the groin and under the armpit. One theory suggests that it provides a large surface area for the natural smell of sweat to disperse from. Many animals use the odour of sweat to attract the opposite sex.

Sweating it out

Teenagers are renowned for their smelly bedrooms. This is not just because they cannot be bothered to wash. Teenagers do start to sweat in a slightly different way.

Humans have two types of sweat glands. 'Eccrine glands' are found all over the body and produce a slightly acidic watery fluid. When this sweat evaporates from the skin it cools the body down. Humans rely on this sweat to control body temperature. It has no odour of its own, but does start to smell when bacteria on the skin's surface begin to digest it.

Take a close look at some fatty sweat. You will need Flash Player, it for free.

Smelly sweat

An altogether stinkier kind of sweat is produced by the 'apocrine glands'. These glands only start working at puberty. They secrete a thick, waxy, greyish substance which is diluted by fluid from other glands nearby. Although it has no odour itself, when bacteria start decomposing it, it releases a strong distinct smell - BO.

Apocrine glands are only found in the armpits, belly button area, ears, groin and nipples. The sweat they produce has no role in temperature regulation. It is released in response to stress, emotion and sexual excitement.

Apocrine glands are related to the scent glands of animals. In other primates, the scent produced by such glands is thought to act as an erotic attractant. How the odour of rotting apocrine sweat might be used by humans is still a mystery which is being investigated.