Octocrylene
In plain terms
A chemical sunscreen filter that also stabilizes avobenzone. The ingredient itself is fairly low-toxicity, but it slowly breaks down into benzophenone, a regulated carcinogen, and that amount climbs as the product ages.
What the evidence shows
Octocrylene is a chemical sunscreen filter that also stabilizes avobenzone, and on its own it is one of the less worrying chemical filters: Europe's safety committee judged it safe up to 10%, it shows little cytotoxicity in lab tests, and its own hormone activity is considered too low to matter at the doses skin receives. The complication is what it turns into. Octocrylene slowly breaks down into benzophenone, and the amount builds as a product ages, a process first measured across seventeen commercial sunscreens. Benzophenone is the problem: it is classified as possibly carcinogenic to humans, acts as a hormone disruptor in animals, and Europe banned it outright from cosmetics in 2023, while California allows no safe threshold for it in personal care. Even the committee that cleared octocrylene flagged the benzophenone it generates as a hazardous impurity to monitor and minimize. How much reaches the body through skin is debated and the amounts are small, so this is not proof that octocrylene products are harmful. But it is an ingredient that converts, on its own, into a regulated carcinogen you cannot see on the label, and it carries a separate environmental cost that has put it on reef-protection lists. Since stable mineral filters do the same job without generating any of this, the cautious choice is to favor them: a reason to switch filters, not to skip sun protection.
On the label
Listed as octocrylene. It often appears alongside avobenzone, which it stabilizes, so the two tend to travel together. A mineral sunscreen based on zinc oxide or titanium dioxide sidesteps both the benzophenone question and the degradation issue; if you do use one with octocrylene, a fresh, in-date product carries less of the breakdown product than an old one.