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Q. Is it true that sunscreens create free radicals in the skin?

A. Yes.

This past August, researchers at the University of California gained wide media attention when they announced that three commonly used sunscreen ingredients can produce skin-damaging free radicals if the sunscreen is not reapplied at regular intervals throughout the day when skin is exposed to sunlight.1

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.

3. Wear high-SPF broad-spectrum sunscreen when in direct sunlight. The American Academy of Dermatology has determined that an SPF of 15 offers high enough protection for most people. Broad-spectrum protection means that the sunscreen protects from both UVB and UVA rays.


4. When in direct sunlight, reapply sunscreen often. The Skin Cancer Foundation recommends high SPFs be reapplied every two hours—more often when swimming or sweating—even with a product touted as resistant or very resistant to these activities. Apply generously wherever skin is exposed to sunlight. Advise clients to use the two-finger rule: Apply a line of sunscreen one-eighth inch wide down the lengths of their index and middle fingers. This amount is enough to cover the entire face, ears, neck, throat and upper chest. The rule applies regardless of whether the sunscreen is in the form of a moisturizer, foundation, blush or dedicated sunscreen product. Be sure to emphasize this even when clients apply sunscreen in foundation or moisturizer. Some people may prefer to apply a separate sunscreen to ensure that they get enough protection.


5. Explain to clients that sunscreens are a last resort when sunlight cannot be avoided. No sunscreen completely blocks UV light, regardless of its SPF. In order to fully protect skin from UV exposure, remind clients to stay out of the sun as much as possible and to cover up when they’re in direct sunlight, sitting by a window or in a car. UVA rays—the sun’s aging rays that may be linked to melanoma—can penetrate glass. For this reason, wearing a high-SPF broad-spectrum UVA/UVB sunscreen daily is a good idea.