Tanning is the body's protection against UV radiation. A good tan reduces UV penetration to the lower layers of the skin by about 90 percent. Some molecules in our bodies, such as DNA and protein, absorb UV radiation and can be damaged by it. Because DNA contains instructions to the cell about how to function properly, damage to DNA can be very dangerous and sometimes causes cancer. So protection from harmful UV radiation by tanning is a natural way of staying healthy.
Skin contains special cells, called melanocytes, which deposit dark pigment in the skin.
Inside these cells, in compartments called melanosomes, the pigment melanin is synthesized by a multi-step biochemical pathway. Once the melanin is produced, it is moved outside the cell, coloring our skin. Sunlight affects this process because UVB radiation activates the first enzyme of the biosynthetic pathway. This increases the melanin production, which increases the amount of color in your skin. We see the result as tanning.