Beauty, they say, is only skin deep. So is the colour of the skin. Some of us are fair, others not so much. What is it that makes the skin of some more fair than others? The answer to this question lies in the production of a substance called melanin by special cells called melanocytes in the skin.
You must have noticed, that when you spend a lot of time in the sun, your skin becomes darker than usual. This is because the body increases the production of melanin. Melanin is nature's way of protecting our skin from the ultra violet(UV) rays of the sun. Melanin absorbs the UV radiation in sunlight, thus protecting the cells from direct exposure to UV and the damage thereof. Prolonged exposure to UV light can cause skin cancer.
How does the body know when to produce melanin?. Amazingly, the eye, not the skin, serves as a detector of sunlight!!! When the eyes detect more sunlight, the nerve connections to the eye, called the optic nerve, sends a message to the master gland, (otherwise called the pituitary gland) at the base of the brain. This in turn stimulates the melanocytes to produce more melanin. Thus, whenever the body is exposed to sunlight, melanin production increases.
The amount of melanin in the body varies from race to race. People living in the warmer regions of the world, have more melanin, as compared to those in the colder regions as their skin needs constant production of this substance. Which is why people in the warmer regions have a darker complexion. Similarly when people from the colder regions spend more time in the sun their skin has the risk of becoming sun burnt. They protect their skins by applying lotions that screen their skin from direct exposure to the harsh rays of the sun.
Melanin is also present in the iris of the eye, this is what gives the eye its characteristic colour.