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Mexoryl™ is the commercial name of two ingredients found in some sunscreens sold by the L'Oreal® company. Mexoryl™ SX, also known as ecamsule, is said to provide better protection against ultraviolet A (UVA) rays than most other sunblocks on the market. Mexoryl™ XL, also known as drometrizole trisiloxane, provides excellent protection against both UVA and ultraviolet B (UVB) rays. Mexoryl™ can be found in sunscreens sold in Europe, Canada and other nations, but is only available on a limited basis in the United States.
Sunscreens work by blocking radiation in the ultraviolet spectrum — light with a shorter wavelength than visible light. Of the ultraviolet light that penetrates the atmosphere to reach the earth's surface, most is classified as UVA or UVB. UVA rays are believed to cause wrinkles and may have other health effects, including contributing to cancer. UVB rays are believed to cause sunburn and skin cancer.
Most commercial sunscreens are effective at blocking UVB rays, but considerably less effective at blocking UVA rays. Mexoryl™ suncreens are noted for closing this gap. Sunscreens with ecamsule in them are said to better block short-wave UVA rays to provide more effective UVA blocking and protection against the sun's long-term effects. Additionally, Mexoryl™ is photostable, meaning that it doesn't break down in sunlight as many other active sunscreen ingredients are known to do. It works by transforming ultraviolet radiation into heat which also helps protect against sun damage.
Ecamsule is an organic compound with the formula C28H34O8S2. It, by itself, doesn't block the entire ultraviolet spectrum and must therefore be combined with another sunblock to provide full protection. Drometrizole trisiloxane is an organic compound with the formula C24H39N3O3Si3. The two are often combined together to provide strong, comprehensive sun protection. They may be used to create sunscreens with very high sun protection factors (SPF), such as SPF 60.
L'Oreal® owns the patents on both chemicals, and all sunscreens containing Mexoryl™ are sold by L'Oreal® or one of its subsidiaries. These include the Anthelios™ line, sold under the La Roche-Posay® label, and Ombrelle™ by L'Oreal®.
In the U.S., the Food and Drug Administration (FDA) prohibits the sale of suncreens containing drometrizole trisiloxane, and, since 2006, has only allowed ecamsule to be sold under limited circumstances after. Ecamsule itself is not approved for sale, but some suncreens containing it as an ingredient are. The FDA has not clearly stated its reasons for prohibiting the sale of Mexoryl™. The compounds do not penetrate the skin, and thus are widely believed to be safe.