Study Shows Why Mixing Your Sunscreens Might Not Be a Good Thing to Do - ScienceAlert

"We still recommend consumers use sunscreen," says materials scientist Richard Blackburn from the University of Leeds, "but suggest they should be careful to avoid mixing sunscreen with zinc oxide, whether intentionally with hybrid sunscreens that combine small-molecule UV filters with zinc oxide, or incidentally by mixing sunscreen with other products containing zinc oxide, such as makeup containing SPF.".

The chemicals approved for sunscreen have only been determined to be non-toxic on their own, as a pure individual chemical, not a blend of chemicals.

To better understand how the chemicals approved for sunscreen in the United States and Europe react when combined, researchers tested the ingredients found in five commercial sunscreens with a sun protection factor of 15.

"These results suggest that zinc oxide particles may increase sunscreen toxicity in ways not currently recognized," the authors write.

"We fear that the increasing ubiquity of UV-filters (in particular metal oxide particles), coupled with the lack of studies on sunscreen phototoxicity, especially as formulated products, is likely to result in products that have unintended consequences and regrettable chemical substitutions," they add.

In Europe, on the other hand, there are other inorganic ingredients that are approved for use as a sun filter, and these don't seem to break down and produce as many toxic chemicals as zinc oxide.

Filling that vast gap in knowledge is a daunting task, made even more challenging by the fact that chemicals could very well become toxic with even a slight change in a formula or a mixing of multiple products