In a province as sunny asAlberta, wearing sunscreenin the spring and summeris important. What’s notas well known is the mathbehind sun protection factor(SPF) numbers. Many of usassume “more is more” anduse a higher SPF sunscreenbelieving we’re gettingstronger protection, but that’snot quite how it works.
The SPF of a sunscreendoesn’t refer to its strength,but rather to the amount oftime it will (theoretically)protect you from UV rays.
(See sidebar.) Likewise, if you
is about time, not strength
Knowing the math behind numbers
apply sunscreen with SPF 30,you should max out your sunexposure at 300 minutes.
While a higher SPF will haveyou out in the sun longer, itdoesn’t mean SPF 30 is twiceas strong as SPF 15. Sunscreenwith SPF 15 blocks 93 percent of UVB rays, while SPF30 blocks 97 per cent—that’sa small difference in theireffectiveness.
In the end, it is best not to
bother getting too hung up
on the math. Patrick Curley,
a program co-ordinator for
Alberta Health Services’
Environment Unit, warns
those calculations don’t
always reflect real life. SPF is
determined in a lab setting,
says Curley. “In reality, there
are so many other factors
related to sun exposure that
are not controlled.”
The damage from UV
exposure is a result of both the
length of time you are outside
and the UV index, which ranks
the strength of ultraviolet rays
on a scale of zero to 11.
“The UV index is affectedby time of day, geographicallocation, season and more,”says Curley. When the UVlevel reaches three or higher,extra sun protection is needed.
How you spend your timein the sun is also a factor. “SPF15 is fine as a minimum if youare running errands or outsidefor brief periods of time, butif you are doing an outsideactivity or working outdoors,at minimum you should applySPF 30,” says Curley.
— Jaelyn Molyneux