We all know that it’s important to wear sunscreen to protect ourselves from the sun’s harmful UV rays, however, most people don’t really understand what SPF is or how the different SPF numbers work. Well, at Eastside Dermatology, we want you to be in the know so that you can be prepared for the summer sun and know exactly what to shop for when it comes to sunscreen.
SPF or sun protection factor notes the ability of a sunscreen to block Ultraviolet B (UVB) rays from the sun, which can lead to a sunburn. SPF measures the length of time it would take a person to sunburn if they were not wearing sunscreen vs. the time it would take with sunscreen on. For instance, if it takes a person 10 minutes to sunburn without sunscreen then wearing SPF 15 would protect 15 times longer (or 150 minutes) for that same person to sunburn.
SPF 15 blocks about 94% of UVB rays, SPF 30 blocks 97%, and SPF 45 blocks about 98%. This shows that SPF 30 is not twice as good as 15, which is a common misconception. Most dermatologists recommend SPF 30 due to the fact that the majority of people do not apply sunscreen as heavily or as often as recommended. For best protection, sunscreen should be applied approximately 20 minutes prior to outdoor activity and heavily enough to cover the surface of the skin. Sunscreen should be reapplied after approximately every 1.5 -2 hours of outdoor activity. Even if your sunscreen says that it’s waterproof, you should always reapply after water exposure.
Most sunscreens do not protect against Ultraviolet A (UVA) light, which reaches deeper into the skin and can cause wrinkles and skin cancer. UVA light comprises about 95% of ultraviolet light from the sun. The best protection from UVA light are physical sun blocks that contain zinc oxide or titanium dioxide.
In addition to sunscreens, some clothing lines contain SPF factor of 30 and can provide additional protection. The FDA is currently in the process of changing the SPF ratings and in the future there may be no sunscreens with an SPF of over 50. These changes are expected within the next year.
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