Ultraviolet Light and Sunscreens – Part 1

Ultraviolet Light and Sunscreens – Part 1

Over one million new cases of skin cancer are diagnosed each year and one in five Americans will develop skin cancer in their lifetime. 90 percent of those cancers will be the result of exposure to ultraviolet (UV) radiation from the sun and tanning beds.

In reasonable amounts, exposure to sunlight is beneficial. Natural sunlight has a germicidal effect and produces vitamin D in the skin. UV radiation can be used to treat rickets, psoriasis, and acne. Exposure to UV rays stimulates the production of melanin that causes a tan and although that tan will help protect the skin from further damage, a tan is a sign that your skin is being damaged and under attack from UV radiation.

About 35 percent of sunlight is visible light, 60 percent is infrared and 5 percent is UV rays (200nm to 400nm). There are two different types of UV rays that reach the earth.

UVB rays (290-320nm) are referred to as the burning rays and are responsible for erythema and tanning. Erythema (redness of the skin) is an inflammatory response, which usually appears within six hours of exposure to UVB rays. Erythema is used to measure the sunscreen’s ability to block UVB rays and determine the product’s Sun Protection Factor (SPF).

An SPF2 blocks 50 percent of UVB rays, which allows you to stay in the sun twice as long as you could without any protection. Increasing the SPF increases the protection but notice, from the chart below, that doubling the SPF from 15 to 30 doesn’t double the protection. It only increases protection by about 2 percent. The increase in protection from an SPF30 to SPF50  is only 1%.

SPF2 blocks about 50% of UVB rays
SPF15 blocks about 95% of UVB rays
SPF30 blocks about 97% of UVB rays
SPF 50 blocks about 98% of UVB rays

UVA rays (320-400nm) are commonly known as black light. UVA plays only a minor role in erythema and tanning, so although its affects are not as obvious or acute as UVB, UVA exposure is every bit as damaging. UVA penetrates into the dermis and contributes substantially to chronic sun damage and the risk of skin cancer.

Remember that SPF only indicates protection from UVB rays and does not indicate protection from UVA rays. A sunscreen with a high SPF may provide adequate protection from UVB rays but offer little or no protection from UVA exposure. Make sure the sunscreen you use is labeled Broad Spectrum.

Unlike organic sunscreens that absorb and react chemically when exposed to UV rays, Inorganic sunscreens physically, reflect UV rays. Inorganic sunscreens reduce the risk of skin irritation and eliminate concerns about unwanted chemical reactions caused by organic sunscreens, especially in the higher concentrations required for an SPF above 15.

Although UV radiation is often referred to as UV light, UV radiation is invisible. Since you can’t see the UV rays that cause sunburn, use sunscreen even on cloudy days. Although clouds block visible light, they offer little protection from damaging UV rays.

Self-tanning products make it possible to tan safely without the sun. Self-tanners contain the ingredient dihydroxyacetone that reacts with the proteins on the skin’s surface to turn golden brown and simulate a natural tan.

We welcome your questions and comments.


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