How The Skin Reacts To Ultraviolet Light

Tanning and burning are two different reactions to exposure to ultraviolet radiation. The first is a protective mechanism in response to the presence of ultraviolet light. The second is the very damage that the first evolved to prevent.

Tanning is simply the proliferation within the skin of a brownish pigment known as melanin, which is produced by a special type of skin cells called melanocytes. Melanin is secreted by these cells following ultraviolet light stimulation. The relative amount of melanin produced in response to this stimulation is determined genetically.

When secreted, melanin is first pinkish in color. As it makes its way toward the surface of the skin, the pigment is oxidized by incoming ultraviolet rays and turns brown. Once it is oxidized, melanin has the ability to absorb harmful ultraviolet radiation, thereby acting as the skin’s built-in protection against the ultraviolet rays.

Tanning can be immediate, delayed or both. Immediate tanning results from the oxidation of existing melanin within the skin. Delayed tanning or pigmentation occurs when the melanocytes are stimulated to produce additional pigment. Sunburn, or erythema, takes place when the ultraviolet exposure exceeds the protection afforded by the existing melanin in the skin. The capillaries in the skin swell, resulting in reddening of the skin, accompanied by increased sensitivity and itching.

All wavelengths of light are not equally effective in stimulating pigment production and causing sunburn. The visible spectrum is relatively ineffective in both of these areas. As the wavelength grows progressively shorter; however, these effects become more pronounced.

Specifically, ultraviolet light in the UVB range can be from 10 to 1,000 times more effective than in the UVA range in stimulating both melanin production and erythema. While the heightened melanin production from high levels of UVB sounds ideal, caution is recommended. Unless exposure is controlled carefully, the effect will be accompanied in most people by moderate to severe sunburn and peeling of the outer skin layers, which robs the body of the melanin that was produced.

On the other hand, UVA causes only mild erythema, which is not even considered sunburn by most. Extremely high levels of UVA are required before the damage causes discomfort. This is why tanning lamps are manufactured to emit mainly UVA rays and only a minimal amount of UVB. However, chronic overexposure to UVA radiation has been linked to a breakdown of the elastic fibers in the skin, resulting in wrinkling and the development of a leathery texture.

The absolute UV output of a tanning lamp is dependent on a number of factors, including the unit in which it is installed, specifically the condition of the starters, ballasts and acrylic. The only way to come up with raw UVA/UVB output levels to compare different lamps would be to measure their outputs when installed in the same fixture. So far, no objective comparisons of this variety have been made public.

Without knowing the actual intensity of the ultraviolet produced by a lamp, the UVB percentage is, at best, an incomplete indicator of its tanning abilities. It is quite possible for a lamp emitting a higher amount of UVB than another to have a lower UVB percentage, simply by also emitting a proportionally larger amount of UVA. Both pigmentation and erythema are markedly more pronounced in the UVB range (280 nm to 320 nm) than in the UVA range (320 nm to 400 nm).