Ecamsule (USAN, trade name Mexoryl SX, INCI terephthalylidene dicamphor sulfonic acid) is an organic compound which is added to many sunscreens to filter out UVA rays.

Ecamsule is a photostable organic UVA absorber, meaning it doesn't degrade significantly when exposed to light.

This is in contrast to the widely used UVA absorber avobenzone that is not intrinsically photostable and requires photostabilizers to prevent significant degradation in light.

A broad spectrum sunscreen with ecamsule, avobenzone and octocrylene significantly reduces the skin damage associated with UV exposure in human subjects.

[9] In studies done in mice it reduces the formation of UV induced pyrimidine dimers and delays the onset of skin cancer.

[13] Because ecamsule is an acid it needs to be neutralized in order to be used without offsetting the final pH of the sunscreen too much.