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Sunscreen 101: Sunscreen, UVA and UVB Rays, Skin Damage and SPF

Posted on October 17, 2016

I recently spent the weekend at the lake and came home looking like a lobster. When it hurt to put clothes on for work and I shivered in the 90 degree weather, I knew I’d gotten far too much sun. The worst part is that I wore sunscreen all weekend, kept applying it, and I could never feel that I was getting burnt! This made me wonder if the sunscreen was bad – or was I using the wrong type? What does SPF even mean?

Needless to say, I realized I knew absolutely nothing about a product I use so often. I did some research and came up with this:

Sunscreen is important year round! We use sunscreen to block ultraviolet (UV) light from damaging our skin. The two types of UV light are UVA and UVB. UVA has more long-term damaging effects on the skin whereas UVB causes sunburn. No matter the temperature outside, UV rays exist and can be harmful to the skin. We can use sunscreens with different SPFs to protect against the harmful effects. SPF stands for sun protection factor and can range anywhere from 2 to 100. This number can be used in this equation:

Minutes to burn without sunscreen x SPF number = maximum sun exposure time.

Theoretically, if you were to normally burn after 10 minutes in full sun without any protection, and you applied a 30 SPF sunscreen, you would not burn for 300 minutes or 5 hours. So one application should do it for the day, right? Wrong! Research indicates proper and repeated application is more important than the SPF number. People sweat, swim and are active while outside and the protection slowly drips away (even if it claims to be sweat proof or waterproof).

SPF 30 filters out about 97 percent of the UVB rays which would cause you to burn, so as long as you keep reapplying after sweating or getting wet, I would think that you shouldn’t need to buy anything much higher than a 30. The American Academy of Dermatology recommends choosing a sunscreen with an SPF of at least 30, but states you start to get diminishing returns with an SPF above 50. They say that higher number SPFs offer slightly more protection, but also contain more chemicals — and no sunscreen can block 100 percent of the sun’s rays.

So there you have it – choosing a sunscreen with SPF between 30 and 50 is your best bet, as long as you remember to keep applying throughout the day, no matter the time of year!


Written by Leah Miller who is a temporary intern with "Thrive." She received her Bachelor of Science in Dietetics from North Dakota State University in Fargo, ND, and is now enrolled in the Dietetic Internship Program with the University of Oklahoma Health Sciences Center. Leah has passions for cooking, cats, traveling, and nordic skiing.

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