Summer is due to arrive in the US on June 20, 6:34am EST. This means it is time to slather on some sunscreen - do it early and do it often. The US FDA, which regulates sunscreen, among other stuff too numerous to mention says, any sunscreen that is (Sun Protection Factor) SPF15 or above, and carries the label "broad spectrum," must provide protection both from both UV-A and UV-B light. Any sunscreen SPF14 or below, or that is not labeled "broad spectrum," is primarily only useful for protection from UV-B light and against sunburn only. Other countries have started providing measurements for UV-A protection on their products, but not the US, yet.
Broad spectrum protection blocks both UV-B and UV-A light, which means you reduce your risk of sunburn as well as skin cancer. UV-A light, which has a much longer wavelength and penetrates deeper into the skin can also cause skin cancer.
SPF numbers are a simple metric, if you could stay in the sun for 10 minutes without getting a sunburn, SPF15 sunscreen would increases the length of time you can stay out in the sun by 15, so you should be able to stay in the sun for 150 minutes without getting burned. In addition, a higher SPF should prevent more UV light from affecting your skin.
SPF15 absorbs 93.3 percent of UVB rays, SPF30 absorbs 96.7 percent, and SPF50 absorbs 98%. Anything above 30 is probably not necessary and 50 or more is essentially a waste of money with little additional protection.
There are two basic kinds of sunscreens: physical blockers and chemical blockers. Physical blockers use minerals to deflect the UV rays away from the skin. Chemical blockers absorb and filter the light to prevent its damaging effects.
Sunscreen manufacturers are no longer allowed to claim their products are "waterproof," because none are. They can claim that their sunscreens are water resistant for instance 40 minutes, after which it should be reapplied.
Interesting to note that Australia is the skin cancer capital of the world with two in three getting skin cancer before age 70.
Bottom line, Consumer Reports found 74 percent of the physical blockers they tested failed to match their labeled SPF. For best results, go for broad spectrum SPF 30 to 50. Unlike politicians, sunscreen is better when you lay it on thick - and often.