NEW YORK, Jan 14 (Reuters Health) -- Sun protection factor (SPF) -- the
number that indicates the level of protection a product offers against
ultraviolet rays -- has had its day in the sun, according to a British
researcher.
Instead of the current system of numbers, manufacturers should adopt
"low," "medium," "high," and "ultrahigh" to indicate the level of protection a
product offers, suggests Professor Brian Diffey from Newcastle General Hospital
in the UK.
"These qualitative measures are intended to encourage people to focus more
on protection than on extending their exposure time in the mistaken belief they
are adequately protected," Diffey told Reuters Health in an interview.
He said many people believe the numbers indicate how much longer it takes
for the skin to burn when covered with sunscreen, than when unprotected.
Actually, the numbers indicate a ratio of the least amount of ultraviolet
radiation it takes to turn protected skin slightly red, to the amount of
radiation it takes to produce light redness in unprotected skin, he explains in
the January 15th issue of the British Medical Journal.
"This mismatch between expectation and realisation may be one contributing
factor to why use of sunscreens has been reported to be a risk factor in
melanoma," Diffey suggests. Melanoma is relatively rare, but is more dangerous
than other types of skin cancer.
He cites a study that found people who say they usually or always use
sunscreen with SPF of 15 or higher are more likely to burn than those who rarely
or never use sunscreen.
The reason, Diffey said, is that most people apply far less sunscreen than
was used in a test by the manufacturers. Most people probably receive 20% to 50%
of coverage, he estimates.
"So the likely explanation for people getting sunburnt despite using high
factor sunscreens is that inadequate amounts of sunscreen were applied or areas
of the body were missed, or both, coupled with overexposure to the sun in the
belief that they were protected," Diffey writes.
He argues that if people applied sunscreen properly there would be no need
for SPF higher than 15 to prevent sunburn.
However, the risk of overexposure to the sun cannot be avoided entirely,
he said.
