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 The doctors tended to underestimate the effectiveness of sunscreens
when they were presented with information on how much radiation is
absorbed by the sunscreen, say the authors.
"Ultraviolet (UV) radiation exposure from the sun and artificial UV
sources is the major cause of skin cancer and premature skin aging,"
lead author Stefan Herzog told Reuters Health in an email.
"The sun protection factor (SPF) is the best known sunscreen
parameter. It conveys a sunscreen’s effectiveness in protecting
against the UV radiation that causes sunburn," said Herzog, a
researcher at the Max-Planck Institute of Human Development in
Berlin.
Herzog said the UV radiation that causes sunburn is also known as is
erythema (redness)-inducing radiation, or EIR.
"The SPF is defined as the ratio of the EIR dose that induces the
first visible redness on sunscreen-protected skin to the EIR dose
that induces the same redness on unprotected skin," Herzog said.
Herzog said that when it comes to skin damage, what matters is how
much of the radiation is transmitted through the sunscreen to your
skin and not how much is absorbed by the sunscreen.
Doubling SPF, for example from 30 to 60, cuts the amount of
radiation transmitted to the skin by half, thus protection is
doubled, the researchers write in JAMA Dermatology.
Herzog and his colleagues wanted to know whether dermatology experts
are able to adequately assess differences in sunscreen protection
based on SPF, the percentage of EIR absorbed by the sunscreen or the
percentage of EIR transmitted through the sunscreen to the skin.
A total of 261 dermatology experts from Germany, the U.S.,
Switzerland and Australia participated in the web-based test. The
doctors were asked to assess the increase in protection for 10 pairs
of sunscreens with different SPFs.
Each sunscreen pair had effectiveness information presented as SPF,
the percentage of EIR absorbed by the sunscreen or the percentage of
EIR transmitted to the skin.
The doctors were asked which sunscreen in each pair would protect a
person longer and how much more effective one was compared to the
other. On average, the doctors underestimated the protection ability
of all the sunscreens, especially when they were presented with
percentage of EIR absorbed. The underestimates were smallest when
information was presented in terms of SPF.
"For effective communication of sunscreen effectiveness, we
recommend to only use SPF. Don’t get too fancy and just stick to the
SPF," Herzog said.
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Unfortunately, big increases in SPF look “small” when expressed as
proportion absorbed, he said, so dermatologists underappreciated the
increase in protection that comes with higher SPFs.
"To curb the skin cancer epidemic, health-care professionals should
understand the basics of the SPF and should consistently advise
patients to use high to very high SPF sunscreens," he said.
Herzog suggests looking for SPFs of 30, 50 or more and a "broad
spectrum" claim on the product labels.
Sun protection is not limited to just using sunscreens, he noted.
Seeking shade and wearing protective clothing whenever possible are
also important.
"Even dermatologists can miss the nuances of what exactly SPF or sun
protection factor really means from the physics standpoint," said
Dr. Steve Xu, a dermatologist at Northwestern University Feinberg
School of Medicine in Chicago who wasn't involved in the study.
"For consumers, it's important to know that SPF is a laboratory
measure of a sunscreen's strength," Xu said, adding that there are
several things a consumer should consider when picking a sunscreen
product.
"I recommend consumers pick sunscreens that they find affordable,
like to use in regards to smell, color and how it feels on the
skin," he said.
The sunscreen should offer broad spectrum protection and water
resistance if there is going to be exposure to water or high ambient
temperature, Xu added, and sunscreen should have an SPF of 30 or
higher, but even that isn’t sufficient on its own.
"A higher SPF offers an extra level of protection in the real world.
But, consumers have to apply enough sunscreen and reapply frequently
enough to ensure protection regardless of the SPF on the label," Xu
said.
SOURCE: http://bit.ly/2kHwQFV JAMA Dermatology, online February 1,
2017.
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