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Sunscreens: What You (and Your Clients) Need to Know
By: Charlene DeHaven, MD
Posted: May 1, 2014, from the May 2014 issue of Skin Inc. magazine.
All sunscreens are designed to prevent the transfer of energy from solar rays to skin. Results of solar energy striking skin over time are sunburn, uneven pigmentation, photoaging and an increased risk of skin cancer. The consistent application of adequate amounts of sunscreen lessens all these risks. Even one severe sunburn increases the risk of skin cancer, so sun-damage prevention is a very important issue. Ninety percent of nonmelanoma skin cancer and 65% of melanoma skin cancer are related to UV exposure.1 Up to 90% of all skin changes related to aging are caused by sun exposure.2 Although clients with darker skin types (Fitzpatrick V and VI) may have a decreased risk of skin cancer, UV exposure still significantly increases their chances of developing the condition.
Types of sunscreen
Although they chemically behave differently, there are two broad sunscreen classifications, both of which decrease solar damage by either blocking or absorbing solar energy transfer: physical sunscreens and chemical sunscreens.
Physical sunscreens. Physical sunscreens help prevent solar energy from striking the skin. Although very efficient at deflecting the sun’s rays, a small amount still penetrate the sunscreen barrier and strike skin where they can be absorbed. Zinc oxide and titanium dioxide are physical sunscreens. Physical sunscreens are inert, meaning they do not react with skin. Because they do not affect skin negatively and do not cause skin sensitivity themselves, physical agents are usually preferred for sun protection.
Chemical sunscreens. There are a large number of chemical sunscreens. All work by absorbing solar energy themselves and transforming it into a chemical reaction, thus preventing transfer of this energy to skin. After absorption of the sun’s energy into the chemical sunscreen molecule, one of two things can happen. This molecule can be chemically transformed via a chemical reaction into another chemical, which is then very quickly converted back to the original sunscreen molecule, ready to absorb another packet of solar energy. This first type of reaction is the most common.
An alternative chemical reaction can occur, which produces a toxic byproduct that itself is carcinogenic. Considerable debate has occurred about how great a problem these small amounts of toxin really are, and if they could potentially increase skin cancer risk. Present consensus is that there is an overall decrease in skin cancer risk from using sunscreen, even allowing for the carcinogenicity of the small amounts of byproduct produced.