Page 42 - Purple Butterfly 1

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unit 1
4. Extension to Science
The Science of Hair
Have you ever thought about hair? It would be strange if you hadn’t. Everybody has hair, after all. When we mention hair, you probably just think of the hair on your head but the human body has hair all over. Some you can see very easily, like the hair on your head, but not all hair is as easy to see.
Hair isn’t just a decoration; it is actually very important. It has different functions depending on where it is. Eyebrows and eyelashes, for example, protect your sensitive eyes from sweat and harsh light, and the hair on your head protects you from the cold and sunburns.
Almost every part of your body has follicles, which are cavities that contain the hair. Each follicle grows its own hair. Where it is located on your body defines how long the hair will grow. Hair on your head can grow from 2 to 6 years, while a hair on your arms will stop much sooner.
Hair is made out of a protein called keratin. Once it begins to grow through your skin, the cells inside it die. All of the hair you can see is made out of dead cells, which is what makes a haircut painless!
Most hair follicles have a sebaceous gland attached, which is also known as an oil gland. These, as it name states, produce oil, which makes hair slightly waterproof and shiny. Sometimes too much oil can be produced, which can make hair look greasy.
You have more than 100,000 hairs on your head, but almost 100 fall out each day. These are constantly replaced since hair goes through cycles. First it grows for some time, stopping for a few months before falling out. This is replaced by a new hair, which also follows the cycle, and so on. Unlike most animals, humans’ hair falls out randomly, not seasonally.
A Rainbow of Hair
Look around at your classmates. What kind of hair do they have? Is it dark and straight, blonde and curly, brown and wavy? Hair color is created because of melanin, a substance that also gives skin its color. The more melanin you have, the darker your hair will be. A blond person will have much less melanin than someone with black or dark brown hair. Melanin is also the reason some people’s hair turns white or gray as they get old. When people age, they lose melanin, and their hair becomes lighter.
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Hair
Follicle
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