By Dr. Joseph J. Hong
Editor’s Note: The South Jersey Catholic Medical Guild of the Diocese of Camden is a Catholic organization of men and women in healthcare. Its purpose is to uphold the principles of the Catholic faith and morality as related to the science of medicine.
One of the most common questions I am asked in my dermatology practice is, “How come I burned even though I wore sunscreen?”
This raises some of the problems with sunscreens as well as their benefits. Sunscreens and sun blocks are designed to decrease the effect of the sun’s rays on your skin. The SPF, or Sun Protective Factor, is a calculation on how long you can stay out in the sun without burning relative to your skin type. If you would normally burn in 10 minutes of sun exposure, when you wear SPF 15, it would now take you three hours to burn.
This equation seems simple, but people often burn anyway. This is predicated on several factors including: a patient’s skin type, application of the sunscreen and misunderstandings about sunscreens. Some sunscreens are water soluble, meaning that they are easily removed in water. This is great when you want to remove them using a simple soap and water rinse. If you are swimming or sweating, this sunscreen will also be removed from your body within minutes. Water resistant and waterproof are terms used to convey that the sunscreen will stay on for 45 and 90 minutes respectively.
Another common misperception is that sunscreens work when put on regardless of the amount. Sunscreens are tested with a very thick layer, which most people do not do with the average application. Most are only applying a third or fourth of the amount tested and are therefore achieving only a relative percentage of coverage. It is important to use a high SPF (I usually recommend over SPF 30) and apply thickly. A simple rule is a shot glass of sunscreen will cover most people. Most sunscreens will only last a few hours, so reapplication is critical to achieve maximum protection. Generally, a reapplication every two hours is sufficient.
I also prefer mineral sunscreens such as zinc or titanium oxide as the active ingredient. These are usually found in sunblock and should be in concentrations greater than 15%. The sunscreens that contain avobenzone or oxybenzone absorb the sun via a chemical reaction. Some patients with sensitive skin will have an almost allergic reaction. Another negative to the benzone sunscreens is that when applied to the entire body, the sunscreen chemicals were found in the blood when blood testing was done. It is unknown if this is toxic or what problems this can cause, but I think this is another reason to stick with the inert mineral blocks such as zinc or titanium. The biggest negative of these mineral sunscreens is that they go on very white, which can be cosmetically concerning.
Oftentimes better than sunscreen is clothing. An average new T-shirt will have an SPF of 15. The sun protective factor will decrease as it is washed and the weave becomes thinner. A thicker or heavier shirt such as a polo shirt or oxford will have an SPF of 30. Clothing can be a good gauge of your sunscreens effectiveness: If you apply SPF 50 on your arms and see a tan line where your T-shirt ends, you know that your sunscreen is working at a rate less than SPF 15. This is probably because you are not applying the sunscreen thickly enough or not reapplying the sunscreen often enough.
Better than sunscreen and clothing is timing. If you are planning a walk on the beach, try to go later or earlier in the day or evening. The sun’s rays are much less with the waning of the day than at midday, when the rays will be at their peak. By following these rules, you can enjoy the beach this summer and prevent skin cancer and the pain of sunburn.
Dr. Joseph J. Hong is a member of the South Jersey Catholic Medical Guild of the Diocese of Camden
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