Phenylbenzimidazole sulfonic acid

Phenylbenzimidazole sulfonic acid (INCI), abbreviated as PBSA and also known as Ensulizole (INN) is a common sunscreen agent. In 1999, the United States Food and Drug Administration regulated that the name ensulizole be used on sunscreen labels in the United States.

PBSA is primarily a UVB protecting agent providing only minimal UVA protection. The scope of UVB is 290 to 340 nanometers whereas the UVA range is 320 to 400 nanometers. For better UVA protection, it must be paired with avobenzone, titanium dioxide, or zinc oxide; outside of the United States it can also be paired with a UV absorber of the Tinosorb or Mexoryl types. Because PBSA is water-soluble, it has the characteristic of feeling lighter on skin. As such, it is often used in sunscreen lotions or moisturizers whose aesthetic goal is a non-greasy finish. The free acid is poorly soluble in water, so it is only used as its soluble salts.