Why does human skin grow darker as it is exposed to more sunlight?

Why does human skin grow darker when it is exposed to sunlight, and lighter when it isn%26#039;t? And can another animal%26#039;s skin grow darker from sunlight, like a pig%26#039;s?|||The sun%26#039;s rays contain two types of ultraviolet radiation that reach your skin: UVA and UVB. (A third type, UVC, is absorbed by the earth%26#039;s atmosphere before it reaches you.)





UVB radiation burns the upper layers of skin (the epidermis), causing sunburns, whereas UVA radiation, which penetrates to the lower layers (the dermis), causes tanning. UVA rays are considered the culprit in the aging of skin, and UVB rays are more often linked to skin cancer. However, research suggests that UVA radiation may also play a role in skin cancer.





A tan is visible proof that your skin is being damaged. When ultraviolet radiation hits your skin, it stimulates cells known as melanocytes, which make a brown pigment called melanin. The melanocytes respond to the sun by making even more melanin to protect your skin from the sun. The melanin acts sort of like an umbrella for the skin%26#039;s cells and can give people the brown tint that is a suntan.|||to reduce the amount of vitamin D released into the body.


your body produces vitamin D when it contacts sunlight.


the lighter skinned the more vitamin during sunlight|||Humans have pigmentation in their skin. As we expose it to the sun%26#039;s rays, the pigmentation grows darker. |||i think its b/c the pigments in your skin absorb nutrents from the sun or something. or the suns rays are %26quot;burning%26quot; your skin darker... i think.|||because UV light stimulates melanin to be produced in the cells which darker the skin as a natural UV barrier|||because you are baking your skin.





answer mine ppls


http://answers.yahoo.com/question/index?鈥?/a>|||because our bodies produce chemicals that will help protect us from the sun and these chemicals are dark so that they can absorb the sun light easier.|||your skin uses the sunlight to create melatonin, which helps prevent more damage by the sun.|||its due to chemical change in our skin,


you%26#039;ll learn about it when you take chemistry %26amp; biology.|||it grows darker becuae it is exsposed to more sun rays which causes it to burn and grow darker|||Melanin It%26#039;s your bodies own protection from the sun. |||because the sin is burning so it gets darker|||melanin...|||Because it burns