Some sunscreens may increase skin cancer risk
According to the Centers for Disease Control and Prevention, 53,919 people in the United States were diagnosed with melanoma skin cancer in 2006, and in the same year 8,441 people died as a result of this disease. The rates of skin cancer are increasing as the result of unprotected sun exposure and the use of tanning beds.
Sunscreens can prevent skin cancer as well as wrinkles and skin discolorations. Sunscreens, also known as sunblock or sun creams, are lotions, sprays, gels or other topical products that absorb or reflect some of the sun's ultraviolet (UV) radiation and help protect against sunburn.
In addition to the sun-blocking chemicals, sunscreens often have retinyl palmitate, a form of Vitamin A, which in theory should be good for the skin. Vitamin A is an ester, primarily retinyl palmitate, which is converted to an alcohol (retinol) in the small intestine. Vitamin A is needed by the retina of the eye for night vision and color vision. Vitamin A deficiency is estimated to cause approximately 250,000 to 500,000 cases of blindness per year in children of developing countries. Retinoic acid, the oxidation product of Vitamin A, acts as an important hormone-like growth factor for epithelial and other cells.
Retinyl palmitate, or vitamin A palmitate, is the ester of retinol (vitamin A) and palmitic acid. Retinyl palmitate is a source of vitamin A added to low fat milk and other dairy products to replace the vitamin content lost through the removal of milk fat. Retinyl palmitate is a constituent of many topically-applied skin care products, including most popular sunscreens. After its absorption into the skin, retinyl palmitate is converted to retinol, and ultimately to retinoic acid, the active form of vitamin A.
However, a possible link has been found between retinyl palmitate in sunscreens and skin cancer. One study found that tumors and lesions developed up to 21% faster in lab animals coated with cream containing retinyl palmitate compared with cream that did not contain it. This may be due to the formation of free radicals that are created when retinyl palmitate is exposed to ultraviolet light.
 Qingsu Xia, et al., Photoirradiation of Retinyl Palmitate in Ethanol with Ultraviolet Light -
Formation of Photodecomposition Products, Reactive Oxygen Species, and Lipid Peroxides, Int. J. Environ. Res. Public Health 2006, 3(2), 185-190, PMID: 16823091
"Our results demonstrate that, similar to irradiation with UVA light, RP can act as a photosensitizer leading to free radical formation and induction of lipid peroxidation following irradiation with UVB light.
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