by Mike Barrett, Natural Society:
A chemical commonly found in sunscreen breaks down into toxic compounds when exposed to sun and water, research shows.
Avobenzone is an oil-soluble compound that is notable for its ability to absorb ultraviolet (UV) light. It is most often an ingredient in sunscreen and cosmetics, including lip balms and moisturizers. The compound converts UV rays into safer wavelengths that don’t damage the skin, and transforms UV energy into thermal energy. 
The chemical was approved by the U.S. Food and Drug Administration (FDA) for use in commercial cosmetics in 1988. It is a known endocrine-disruptor.