Understanding Sunscreens

Sun Protection Factor (SPF) is a multiplier of your skin’s ability to resist burning. So if normally your skin burns after 10 minutes of sun exposure, applying sunscreen with an SPF 10 will increase the exposure time to 110 mins before you get burned.

Sunlight is composed of radioactive rays, which get filtered out by the atmosphere layers of the Earth. Of all the dangerous rays that the sun emits, the ones that reach our skin are the UV rays.

UVB rays stimulate vitamin D production, appearance of moles, and can lead to sunburn with overexposure. There are more UVB rays in sunlight in the summer. UVA rays are responsible for tanning of the skin, as well as negative effects of sun exposure like as wrinkles and melanoma.

The SPF rating that comes on sunscreen bottles is determined by an FDA required in vivo test which involves exposing volunteers’ skin to the sun until it sunburns and then evaluating the protection factor that the sunscreen gave that skin.

Some studies have shown that sunscreen’s protection factor doesn’t rise as evenly above SPF30 as it does in the ratings below. Recently this number has been raised to 50 but keep in mind that SPF50 isn’t twice as good as SPF25.

Look for products labelled as UVA/UVB broad spectrum, and don’t forget to check the ingredients for zinc oxide, titanium dioxide, avobenzone, and ecamsule (aka Mexoryl) which are all effective at blocking UVA.