Some of the world’s most popular sunscreens risk causing cancer if left on the shelf too long because a commonly used sun protection factor breaks down into a harmful ingredient, US and French researchers claim. If left for a year at room temperature, one of the key ingredients in sunscreens breaks down into benzophenone, a “mutagen, carcinogen, and endocrine disruptor”, the study in the Chemical Research in Toxicology review said. Scientists at CNRS, the Sorbonne and the Oceanological Observatory in Banyuls-sur-Mer in France and the Haereticus Environmental Laboratory in the US, made the discovery after experiments on nine commercial sunscreen products from the EU and eight from the US.