Should you trust the SPF number on the label?

Dr. Cole

Shielding your skin from the sun may not be as easy as once thought.

At the current Maui Derm for Dermatologists 2020, Curtis Cole, Ph.D., president of Sun & Skin Consulting, presented on controversies in photoprotection, namely, that it’s not always best to trust the number on the bottle.

Dr. Cole showed a study published by Consumer Reports depicting major differences in the SPF number on the product and their testing results, with some having less than half the value listed on the label.

“Some of the numbers can be found for SPF 50 showed up as an SPF 8,” says Dr. Cole. “This report indicated that as much as 50% of the sunscreens did not meet their label claims and
over 74% of sunscreens with only inorganic (ZnO and TiO2) were overrated in terms of their SPF results.”

With sunscreen research beginning in the 40s, Dr. Cole says it wasn’t until 2010 that the International Organization for Standardization (ISO) created a unified global protocol for SPF testing.

More recently, he has been working with ISO for the last 5 years as their project leader to revise and improve the method for sunscreen SPF testing to give lower variability and higher accuracy.

To do this, Dr. Cole says ISO has taken steps to objectively determine a test subjects skin phototype. Instead of using questions like, “do you burn in the spring?”, he says “we replace that with an objective, instrumental colorimetric and measurement for selection of subjects for the SPF test and prediction of their sunburning dose (Minimal Erythema Dose - MED).”

In his presentation, Dr. Cole also discussed the protection time that skin screens give - all sunscreens are required to state “apply liberally and reapply after two hours” - which is typically too late, and users have already begun to burn. “When people reapply when the FDA recommends at two hours, it’s already too late. 

“Don’t try to calculate ‘safe’ sun time from SPF label numbers and your own ‘burn’ time,” he says. “SPF numbers only give relative value for one product versus another, and are based on laboratory testing and not real sunlight. 

Dr. Cole also recommends people apply two layers of SPF before going into the sun.

“My recommendation is that you apply twice as much because you need the protection…,” he says. “Once it dries, apply again to have a higher chance of [covering] all of the spots that you miss the first time around, and use clothing and broad brim hats as your primary defense against sunburn.”