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The Secret Behind Eyelash Growth and Sunscreen's Dark Side

By: Rebecca James Gadberry
Posted: June 11, 2008, from the November 2006 issue of Skin Inc. magazine.

page 5 of 7

The study, which was funded by grants from the National Science Foundation and the National Institutes of Health, is the first of its type to use a unique two-photon laser fluorescence imaging microscope to visibly track what happens when three widely used U.S. Food and Drug Administration (FDA)-approved over-the-counter UV sunscreens—octinoxate (octyl methoxycinnamate), oxybenzone (benzophenone-3) and octocrylene—penetrate the skin’s surface.

Incorporating commonly used levels of each sunscreen into a standard sunscreen base, the researchers were able to view their physiological effects as they made their way from the skin’s surface into deeper epidermal layers. They found that the oxidizing molecules known as reactive oxygen species (ROS)* are lessened significantly when the sunscreens are applied initially. But once the sunscreens leave the skin’s surface and travel into the epidermis, ROS are generated at a higher-than-normal rate within the epidermis—especially when they enter the lower epidermal layers, where cellular DNA is found. If the sunscreen is reapplied, the amount of ROS declines again.

Kerry M. Hanson, a senior research scientist at the University of California, Riverside’s department of chemistry and the study’s lead researcher, concedes that sunscreens can do an excellent job of protecting against sunburn when they are used correctly, which means high SPFs applied uniformly onto the skin every two hours. She adds, “Our data shows, however, that if coverage at the skin’s surface is low, the UV filters in sunscreens that have penetrated into the epidermis can potentially do more harm than good.”

How do the results of this study affect sunscreen use? Following are some suggestions.

  • 1. Look for sunscreen products that keep the ingredients on the skin’s surface for as long as possible. There are various ways to do this, including avoiding skin-penetrants, binding sunscreen ingredients to larger molecules that inhibit penetration or using silicone-based emulsions. Check with your manufacturer to determine how the company is inhibiting sunscreen penetration.


  • 2. Look for UV-stable antioxidants in sunscreen. In a previous study, Hanson determined that an SPF 15 sunscreen featuring octinoxate and avobenzone reduced ROS formation in lower epidermal layers by 90% when compared to bare skin.2 Adding UV-stable vitamin E acetate and sodium ascorbyl phosphate to the same sunscreen reduced ROS formation by an additional 5.5%, for a total of a 95.5% reduction of UV-generated ROS. Other antioxidants believed to be effective against UV-induced ROS include tetrahexyldecyl ascorbate, glycyrrhizates from licorice, coenzyme Q10 (ubiquinone), idebenone, thermus ferment, ethylbisiminomethylguaiacol manganese chloride, green and white teas with a standardized level of epigallocatechin gallate (EGCG), and pomegranate extract with a standardized level of polyphenol ellagic acid. To ensure that your clients receive additional antioxidant protection from their sunscreens, ask your manufacturer for data that shows that the antioxidants contained in the products are effective ROS-inhibitors during UV exposure.