Sunscreen, or sunblock, works in a variety of ways, but all sunscreens are aimed with the goal of preventing sunburn and skin damage. Sunscreen can protect against ultraviolet-A (UVA) or ultraviolet-B (UVB) radiation, or a combination of both. Regardless of the product and active ingredients chosen, a broad-spectrum sunscreen with a sun protection factor (SPF) of 30 or higher should be applied prior to sun exposure and reapplied at least every two hours, according to the University of California, San Francisco.
UVA Radiation Blockers
Some active ingredients in sunscreen block only ultraviolet-A radiation. This type of radiation is responsible for damaging the layers of skin underneath the surface. For this reason, UVA rays are considered to be the chief contributor to wrinkles, age spots, skin sagging and melanoma--a deadly form of skin cancer. Because UVA rays are present year-round, even when the sun is not shining, a person should wear a UVA protectant year-round.
According to the United States Environmental Protection Agency, chemicals that block UVA rays include avobenzone or a type of benzophenone variety, including dioxybenzone, oxybenzone or sulisobenzone.
UVB Radiation Blockers
Ultaviolet-B (UVB) radiation is radiation that damages the outer layer of the skin. This means UVB rays are responsible for causing sunburns, wrinkling and age spots and can serve as a cause of skin cancer, according to USAToday.com.
Chemicals found in sunscreen that block UVB rays include aminobenzoic acid, cinoxate, homosalate, octocrylene, octyl methoxycinnamate, octisalate, padimate O, phenylbenzimidazole sulfonic acid, sulisobenzone and trolamine salicyate, according to the University of California, San Francisco.
Broad Spectrum Chemicals
While no sunscreen ingredient protects completely against UVA and UVB radiation, some chemicals provide a significant amount of protection for both. Those that protect against each include dioxybenzone, oxybenzone and sulisobenzone.
Other chemicals that contain UVA/UVB protection include titanium dioxide and zinc oxide. These chemicals are known as broad spectrum chemicals because of their ability to block significant parts of UVA and UVB radiation. When the sun's rays hit either chemical, the zinc oxide or titanium dioxide either reflects, scatters or absorbs UVA and UVB rays. Earlier formations of these compounds were opaque when applied, meaning they were difficult to apply to the entire body. However, recent developments have enabled researchers to reduce the size of the molecules, which makes them more transparent when applied, according to the Environmental Protection Agency.
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