Choosing a Sunscreen: The ABC’s of SPF
The sun emits ultraviolet radiation which is arbitrarily divided into ultraviolet (UV) A, B, C, and D. Fortunately the Earth’s atmosphere blocks UV-C and UV-D but UV-A and UV-B still make it to the Earth’s surface. A certain amount of ultraviolet energy is needed by the body to create active vitamin D but there is most certainly too much of a good thing. UV-A and UV-B radiation contribute to premature aging and skin cancer. Fortunately there are ways to protect against the harmful radiation while still enjoying the warming sun’s rays.
Choosing a sunscreen can be a daunting task. There are hundreds of options available all claiming to be the best possible. To choose a sunscreen, keep a few tips in mind.
SPF – Sun Protection Factor
The SPF is a measure of how well a sunscreen protects against UV-B radiation. SPF is determined by choosing a number of fair skinned volunteers and measuring the amount of time it takes for skin to turn red. The product tested is then applied and the time for the skin to turn red is again measured. The difference in time is the SPF. The redness in the skin is caused by UV-B radiation and not UV-A radiation therefore SPF does not measure UV-A protection.
As it turns out, the SPF scale is a logarithmic scale which means that an SPF 15 is about 95% protection and an SPF 30 is about 97% protection. Anything greater is of little to no benefit.
After selecting a product with an SPF of 30 or greater, look at the active ingredients to determine UV-A protection. The broadest protection is afforded by avobenzone, zinc, and titantium. The days of zinc causing unsightly white marks are gone as newer formulations have micronized zinc which works better into the skin. Some sunscreens are even tinted for better blending.
There are no sunscreens which are waterproof or sweat proof. New product labeling will identify how water resistant and sweat resistant products are.
After choosing a sunscreen, using it is important. Apply 30 minutes before exposure, make sure to work it into the skin, and reapply at least every 2-3 hours, sooner if excess water exposure occurs.
Avoidance Is Best
As always, avoidance is even better than sunscreen use. Wearing long sleeves, big hats, and staying inside during high sun times of 10A-4P are always useful.