Roll Out Those Lazy, Hazy, Crazy Days of Sunscreen

Unless you've been living in a cave for the last decade, you've probably heard that you should be using suncscreen.

Health Canada, the Canadian Cancer Society, family doctors, dermatologists and other medical professionals all agree: wearing sunscreen with at least 15 SPF will reduce your risk of sunburn, slow the rate of the aging of your skin, and lower your risk of skin cancer.

Sounds easy. But there's a bit more to it than that. 

SPF is an acronym for Sun Protection Factor. Scientists observe the amount of time it takes a person’s skin to burn with and without sunscreen, when exposed to a constant intensity of UV light. The ratio of these two amount yields the Sun Protection Factor (time it takes to burn with sunscreen ÷ time it takes to burn without sunscreen). Another way to put it: if your skin starts to burn after 10 minutes in the sun without any protection, wearing a SPF 15 sunscreen will theoretically allow you to be exposed for 150 minutes without burning.

(Let us pause here for a moment in recognition of the folks who allowed themselves to be fried in a lab for science. Okay, enough pause.)

But it's not that simple. The intensity of UV radiation you are exposed to will vary throughout those 150 minutes, and the protective layer of your sunscreen can (and most likely will) wear off due to your natural perspiration, your clothes, swimming, or simple evaporation. SPF values calculated in a laboratory may not hold true in the great outdoors.

So here are a couple of hints to to keep your skin safe from the sun:

• Sun Protection Factors are evaluations on protection from UV-B light only, (no UV-A) so be sure to keep your eyes peeled for Broad Spectrum sunscreen. UV-A radiation will not cause the skin to redden or hurt but can cause serious “invisible” damage such as aging of the skin and DNA damage to skin cells which would lead to cancer. Persistent Pigment Darkening (PPD) is UVA’s rating (instead of SPF, but same rules apply with the number value and it’s protection time).

• Don’t trust claims on labels like “All day wear” or “water-proof”. It ain't so. Your protection from UV light depends on how much sunscreen you have on your skin, the intensity of UV radiation you are exposed to from the sun, and the amount of time you spend exposed to sunlight.

Take home message: be informed BEFORE you go outside. The UV Report Index is available through the Weather Network and Environment Canada. And most importantly, apply, and RE-apply frequently (approximately every 30 minutes), dress appropriately, and be careful what you buy.

OR just move into a cave...

from Special Science Correspondent Julia Prokopick