Benzophenone

Benzophenone is a small aromatic ketone. It's worth noting right away that it's a different molecule from the numbered "benzophones" like benzophenone-3.

This ingredient has always had a quieter job. Because it absorbs UV light, it is used in small amounts as a photostabilizer to stop colors, fragrances, and other light-sensitive ingredients from breaking down on the shelf.

It also naturally has a sweet, soft-rose scent.

The reason you'll almost never see it on a modern ingredient list comes down to safety data:

In a two-year dietary studies by the US National Toxicology program, benzophenone increased kidney and liver tumors in rats and mice.

This led the International Agency for Research on Cancer to classify it in Group 2B, "possibly carcinogenic to humans," and California to add it to the Proposition 65 list, effective June 22, 2012.

The EU took this a step further as well: after a harmonized classification as a category 1B carcinogen, Benzophenone was added to the list of substances prohibited in cosmetics, with the ban applicable from December 2023.

In practical terms, this is now a phased-out ingredient across major markets.

Its only main relevance today is as a trace impurity and breakdown product; octocrylene generates benzophenone through a retro-aldol reaction so it's treated as an impurity and degradation product that should be kept at trace levels.