By: Dr. Michael Leher
Playing in the sun, whether at the beach or backyard is a time honored tradition, and everyday sun-exposure is often unavoidable, but getting too much sun can increase your risk of skin cancer and photo-aging (premature skin wrinkles and skin discoloration), not mention those pesky sunburns.
Sunlight is composed of ultraviolet radiation that harms your skin by directly damaging your DNA. Sun exposure and DNA damage leads to the unintended consequences of burns, photo-aging, and increases your risk of skin cancer. To reduce these risks it is prudent to avoid the sun when possible and apply sunscreen when you expect to be in the sun for any period of time. With so many sunscreens on the market though, how do you choose the one that is right for you? What does SPF mean? Am I using enough? What is broad spectrum? What should I use for my child? Why is it so complicated? These are all good questions and hopefully this article will give you some answers and allow you to make the best choice the next time you are in the sunscreen aisle at your local store.
Sunlight is composed of ultraviolet (UV) radiation and is very damaging to your cells and their intracellular machinery. In fact, many scientists use ultraviolet radiation to kill bacteria and other unwanted cells because the UV radiation is so destructive to unprotected cells. UV radiation is broken down into three main categories, UVA, UVB, and UVC based on their different wavelengths; however UVA and UVB are the most clinically relevant and are what many of our sunscreens block. UVA can be divided into UVA1 and UVA2, both of which are associated with photo-aging and increased risk for skin cancer. UVB is the set of wavelengths mainly responsible for sunburn as well as photo aging and causing skin cancer.
Sunscreens are composed of compounds that can either absorb or reflect UV radiation and prevent the damaging effects of UV radiation on skin cells. Sunscreens are broken down into two categories, the physical blockers (Zinc Oxide, Titanium Dioxide) and the chemical blockers (avobenzone, homosalate, etc). The physical blockers (Zinc Oxide, Titanium Dioxide) tend to be less irritating and block UV radiation across the UVA and UVB spectrum. The drawback is that many physical sunscreens can leave your skin with the white chalky appearance so classically seen in old beach movies. The chemical blockers on the other hand tend to have a more narrow spectrum of ultraviolet coverage, however many sunscreen formulations combine several chemical blockers to more adequately cover the UVA and UVB spectrum. Chemical sunscreens also carry a risk of contact allergy and irritation; but this only affects a minority of people.
One of the major metrics by which sunscreens are measured is the Sun Protection Factor or SPF. The SPF is the amount of UV radiation required to cause a mild-sunburn. A SPF 15 means that it will take 15x the UV exposure to cause a mild sunburn when compared to unprotected skin. Remember though, that sunburns are mainly caused by UVB and an SPF may not adequately assess the ability of a sunscreen to block UVA, therefore it is crucial to find a sunscreen that also says “Broad Spectrum”.
There has been some controversy regarding SPF labeling in recent years. The SPF predicts the amount of UV radiation required preventing a sunburn, but its relationship to the amount of UV radiation blocked is not linear. For example, an SPF 15 generally blocks approximately 93% of UV radiation while an SPF 30 may block closer to 97%, and a SPF 45 may block 98%. For this reason, the FDA has recommended that sunscreens not label above SPF 50 because it may provide a false sense of security to consumers. Overall, the American Academy of Dermatology has recommended that an SPF of 30+ with “Broad Spectrum” coverage be used.
One of the most common reasons for a sunscreen to not work effectively is because it is accidently washed off and not reapplied. Many sunscreens can lose their effectiveness after a couple hours playing in the sun, therefore it is important to reapply every two hours or less. If you are swimming it is even more important to re-apply your sunscreen. Sunscreens labeled as “Very water resistant” maintain their effectiveness for 80 minutes before needing reapplication, while those that say “Water resistant” hold their effectiveness for 40 minutes. The FDA recently recommended against the use of the wording “Waterproof” as even the hardiest sunscreen is not resistant to a day in the pool or on the beach.
What about sunscreen for my children? The American Academy of Pediatrics has recommended that sunscreen be used once your child is 6 months old. At birth, the skin barrier is not fully developed and the use of sunscreen before 6 months may cause irritation. Further along this point, many children have decreased function in their skin barrier and the use of physical sunscreens such as Titanium Dioxide and Zinc oxide may be better tolerated in children.
With all that information in mind, how do you chose the right sunscreen? The next time you are at the store, picking out a sunscreen look for a few key words. The American Academy of Dermatology recommends sunscreens that are SPF 30+, Broad Spectrum, and Water Resistant, the rest if up to you! If the sunscreen you purchase has these words you are in good shape. After that, the selection is based on personal feel and style. Many of the physical blocking sunscreens (Zinc Oxide, Titanium Dioxide) have a very broad spectrum of coverage and are less irritating to the skin, the drawback is they frequently leave a mild white tinge on the face and extremities. The chemical sunscreens (avobenzone, homosalate, etc) can be very effective when combined together and tend to rub on with less of a white residue. Chemical sunscreens however tend to be more irritating to the skin for some consumers. Picking out the right sunscreen is important, but if it not on your skin it does you no good! So always remember to reapply every 2 hours or sooner if you are swimming.
The use of a SPF 30+, Broad Spectrum, Water Resistant sunscreen combined with other common sense sun protection measures can help keep your skin looking healthy, young, and safe while you enjoy all your favorite outdoor activities.