For the average tanner, tanning is simply a process that turns skin from a pale, pasty white to a beautiful golden brown; it is a process that can either occur naturally under the sun or in a tanning salon under artificial lighting. In both cases, what is happening to the skin when it tans is actually a chemical response to the skin’s exposure to UVA and UVB rays.

Understanding Ultraviolet Light

UV light from the sun comes in two forms: UVA or ultraviolet-A waves or UVB or ultraviolet-B waves. There is also a UVC ray, but they are absorbed by the ozone layer and do not reach the earth’s surface.

UVA waves are long, solar rays approximately 320-400 nanometers in length. They are less likely than UVB rays to cause sunburn, but UVA rays penetrate the skin more deeply which leads to wrinkling and leathering of the skin. Medical studies have also linked UVA rays to some skin cancers such as melanoma.

UVB waves are short solar rays of approximately 290-320 nanometers in length. Ultraviolet B rays tend to produce sunburn more often than UVA rays and are also believed to be a root cause of skin cancers such as melanoma and carcinoma. UVB long rays are strongest in the summer months when the earth rotates closest to the sun. During the winter, when the earth rotates away from the sun, it is harder to get a "suntan" since the sun’s rays do not reach the earth's surface.

UVB Light and the Skin

The skin is the human body’s largest organ and it is divided into three layers: epidermis, dermis and subcutaneous tissue. The epidermis is the outer layer of skin that tans when exposed to sunlight over long periods of time. The dermis is the second layer of skin and it contains collagen and elastin which aid in maintaining the firmness of the skin; this layer of skin also helps in fighting infections. Finally, the subcutaneous tissue is the third layer of skin that is composed primarily of fats that help bind the skin to the body. This layer of skin serves multiple purposes including insulator and shock absorber.

Skin tanning occurs in the epidermis when melanocytes, a type of cell found in the epidermis, produce melanin, a protein pigment found in the skin, when exposed to UVB rays. UVA rays oxidize the melanin which produces the browning of the skin as a defense mechanism against overexposure to sunlight.

Body's Reaction to UVA

UVA rays pass through the epidermis of the skin and enters the dermis, or the second layer of the skin. The dermis is composed of collagen, elastin, blood vessels, and nerve endings; it provides the firm youthful padding for the skin. Prolonged exposure of UVA cracks and shrinks the collagen and elastin found in the dermis. The more the skin is exposed to UVA radiation, the smaller the layer becomes; eventually the epidermis begins to sag and hangs off the body, resulting in the old, ragged look many older tanners have. This is why it is important to tan in moderation!