Ultraviolet A radiation. The sun produces a range of ultraviolet (UV) radiation, of which UVA and UVB affect our skin. UVA rays have wavelengths of 320 to 400 nanometers; UVB rays have wavelengths of 290 to 320 nanometers. UVB radiation causes sunburn, while UVA radiation does not produce any visible short-term evidence of skin damage. Nonetheless, UVA radiation creates serious cumulative changes in skin that may be far greater than the sunburn caused by UVB radiation. Research has shown that unprotected exposure to UVA rays can, within one week, create distinct injury, such as inflammation, abnormal cell production, thickening of the stratum corneum (outer layer of skin), depletion of immune-stimulating cells, and evidence of the possibility of elastin deterioration (Sources: Journal of the American Academy of Dermatology, May 2001, pages 837–846; Bulletin of the Academy of National Medicine, 2001, volume 185, number 8, pages 1507–1525; Photodermatology, Photoimmunology, and Photomedicine, August 2000, page 147; and Journal of the American Academy of Dermatology, January 1995, pages 53–62). Research also indicates UVA exposure is even more damaging than we once knew: it seems that when UVA radiation hits skin, it not only penetrates to skin’s lower layers (where it destroys collagen and elastin) but the damage “bounces back” like light reflecting from a mirror, giving every layer of your skin a double-whammy of damage. UVA radiation prompts tanning, yes, but the tan you see is direct evidence of your skin responding, as best it can, to the onslaught of damage it just endured.

To be truly effective and beneficial for skin, sunscreens must protect skin from both the sun’s UVA and UVB radiation. In the United States, there are four ingredients approved by the FDA that protect across the full UVA range: titanium dioxide, zinc oxide, avobenzone (also called Parsol 1789 and butyl methoxydibenzoylmethane), and Mexoryl SX (ecamsule). Outside the United States, Tinosorb is another. Mexoryl SX is a L’Oreal-patented sunscreen ingredient that received FDA approval in July 2006 for use in a single sunscreen, Anthelios SX SPF 15, from the L’Oreal-owned line La Roche-Posay. This is the only sunscreen with Mexoryl SX that is approved for sale in the United States (Sources: International Journal of Pharmaceutics, June 2002, pages 85–94; Photodermatology, Photoimmunology, Photomedicine, August 2000, pages 147–155 and; Skin Therapy Letter, volume 2, number 5, 1997; and However, L’Oreal has been adding Mexoryl SX to products in their namesake line as well as in other lines they own, including Lancome and Kiehl’s.

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About the Experts

Paula Begoun is the best-selling author of 20 books on skin care and makeup. She is known worldwide as the Cosmetics Cop and creator of Paula's Choice. Paula's expertise has led to hundreds of appearances on national and international television including:

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The Paula's Choice Research Team is dedicated to busting beauty myths and helping you solve your skincare frustrations with research-supported expert advice—so you'll have the facts you need to take the best possible care of your skin.

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