The ultraviolet radiation that reach the skin are two types of UV-B and UV-A, and are characterized by the different wavelength
UV-A: UV-A rays penetrate into the deeper layers of the dermis (the deeper layer of the skin) tan, but due to their low energy is difficult to get burned.
UV-B: UV-B rays stimulate the production of melanin, determine the appearance of the tan. The rays are absorbed by the epidermis (top layer of skin) and can cause sunburn and skin damage.
As a defense against ultraviolet light, after a short exposure the body tans releasing melanin, a dark pigment.
The amount of melanin varies according to the type and color of the skin.
Melanin helps to block the penetration of UV and prevents that these damage the deep part of the skin (dermis).
A positive effect of UV light that induces the production of vitamin D in the skin necessary for the fixation of calcium for strong bones