Pretty sure age is a big factor. The components of many sunscreens (non mineral) break down into benzene. They recommend throwing out your unused sunscreen after every year.
Thank you for this. This guide mentions that it breaks down when exposed to chlorinated water and UV light -- NOT that sunscreen breaks down in storage over time, which is what I was personally concerned about.
I can't seem to find the article I saw a couple months ago. Here's one on room temperature storage for 1 year. This accelerates if left in a hot car or similar environment.
