Sunscreens Health Article

Definition

Sunscreens are products applied to the skin to protect against the harmful effects of the sun's ultraviolet (UV) rays.

Description

Many brands of sunscreens are available, containing a variety of ingredients. The active ingredients work by absorbing, reflecting, or scattering some or all of the sun's rays. Most sunscreen products contain combinations of ingredients. Sunscreen products are sold as lotions, creams, gels, oils, sprays, sticks, and lip balms, and can be bought without a physician's prescription.

The U.S. Food and Drug Administration requires sunscreen products to carry a sun protection factor (SPF) rating on their labels. This number tells how well the sunscreen protects against burning. The higher the number, the longer a person can stay in the sun without burning.

There are three types of ultraviolet light, based on their wavelength: UVA, UVB, and UVC. UVC has the shortest wavelength and is blocked by the earth's ozone layer. Concerns about the depletion of the ozone layer focus on the serious health effects that increased exposure to UVC light would have.

UVB light is the next shortest wavelength and is called the tanning light since it is light in this range that promotes creation of the skin pigment melanin that creates a tan. UVB light only penetrates the outermost layer of the skin, but it promotes basal and squamous cell carcinoma and may worsen the effects of UVA.

Ultraviolet A is long-wave radiation generated by the sun that penetrates more deeply than UVB, causes wrinkling and leathering of the skin and damages connective tissue. UVA is the light that causes melanoma, the most serious skin cancer.

Several types of chemicals are used as sunscreens. They vary by the degree of protection they can provide and the types of ultraviolet light they can block:

• Cinnamates, such as octyl methoxcinnamate, give low levels of protection, and are only effective against UVB light.
• Para-amino benzoic acid (PABA) compounds, including PABA, padimate O (octyl dimethyl PABA), and glyceryl PABA, are effective only against UVB light.
• Salicylates, octylsalicylate, and homosalate offer moderate levels of protection against both UVA and UVB light, but the range of light waves against which they protect is relatively narrow.
• Benzophenones, including oxybenzone and dioxybenzone, protect against a broader range of ultraviolet light than the salicylates and are more useful for broad spectrum protection.
• Physical sunscreens are really sun blockers and include titanium dioxide, red petrolatum, and zinc oxide. Preparations containing these blockers are thick ointments and are usually reserved for skin areas at high risk of burn, such as the nose.

Other compounds, such as Parsol 1789 (avobenzone), Eusolex 8020, and menthyl anthranilate appear to be valuable broad spectrum agents. In one study, the combination of 3 percent butyl methoxydibenzoyl-methane and 7 percent padimate O was the most effective of all sunscreens tested.

In addition to the chemical used as a sunscreen, the vehicle can be important in determining how well a product works. Unfortunately, thick, greasy ointments seem to work better than vanishing creams, lotions, or liquids.