October 7th, 2009 by admin
What does ‘SPF’ mean?
SPF = Sun Protection Factor SPF or ‘Sun Protection Factor’ is based on a concept called the ‘MED’ or ‘Minimal Erythema Dose’.
(Erythema is just a fancy word for pink or red).
One MED is the amount of ultraviolet light it takes to make a person’s skin turn ‘erythematous’ or pink.
The unit of light is usually measured in time, for example 10 minutes on a sunny day for a fairly light person
and perhaps 20-30 minutes for someone of medium complexion.
A sunscreen is meant to increase the amount of time until a person becomes pink/red or sunburnt.
So a sunscreen with a SPF/ Sun Protection Factor of 10 is meant to allow a person ten times as much time in the sun without turning red or getting sunburnt.
You should know that these SPFs are determined in a laboratory where conditions are ideal:
no sweating, no rubbing the product off with a towel, a uniform application of plenty of product, no swimming etc.
In the real world, lots of things conspire to make the sunscreen less effective.
That is why dermatologists recommend that the sunscreen be re-applied after swimming, sweating, exercising etc.
It is also important to apply enough sunscreen to do the job.
Dr. Albert Kligman, a famous pioneer in dermatology once said that people often mistakenly dab on sunscreen ‘like perfume’, using just a little and expecting it to cover their entire skin surface.
It probably takes about two tablespoons to adequately cover an average person’s skin.
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