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Sunscreen Technology, Regulations and Formulations
By Ken Klein
Posted: March 21, 2007, from the April 2007 issue of Skin Inc. magazine.
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UVB (290–320 nm). This radiation is responsible for almost all sunburns and skin cancer. It has been estimated by Frederick Urbach, MD, of Temple University, that 95% of all skin cancer results from exposure to UVB rays.
UVAI (340–400 nm). This is the least energetic of all UV radiation, but it is the most deeply penetrating. Although they are not responsible for burning, UVAI rays can cause wrinkling and premature aging. In some cases, they can cause DNA damage, and thus, skin cancer.
UVAII (320–340 nm). This type of radiation can cause slight skin reddening and long-term damage.
Sunscreen chemicals are materials that have the ability to absorb energy in the UV range and then give it off at other nondamaging wavelengths, such as heat. Even inorganic sunscreens, such as zinc oxide and titanium dioxide, have this ability. In addition, they can scatter UV and enhance the efficiency of the organic sunscreens.
Sun protection factor (SPF) is a ratio of the length of time a person can stay in the sun at noon before receiving an amount of energy that results in a just-perceptible reddening, which is visible 16–24 hours after exposure. This is also known as an individual’s minimum erythemal dose (MED) using sunscreen, divided by the length of time a person can stay in the sun at noon before receiving an amount of energy that results in a just perceptible reddening not using sunscreen. MED will vary as a function of time of year, latitude, altitude and, of course, a person’s skin color and type. Time of day also plays a major role in sun exposure. For example, at 3 PM, the UVB radiation received is 51% less than that received at noon, according to the book Sunlight and Health by Michael Lillyquist (W. Clement Stone, 1987).
Sunscreen products are regulated as drugs by the U.S. Food and Drug Administration (FDA). So what, according to the FDA, is a