Phenylbenzimidazole sulfonic acid

Phenylbenzimidazole sulfonic acid (C₁₃H₁₀N₂O₃S) 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. Phenylbenzimidazole sulfonic acid is primarily a UVB protecting agent providing only minimal UVA protection. Its scope is 290 to 340 nanometers whereas the UVA range is 320 to 400 nanometers [1]. For complete UVA protection, it must be paired with avobenzone, titanium dioxide, or zinc oxide; outside of the United States it can also be paired with Tinosorb and Mexoryl. Because Phenylbenzimidazole sulfonic acid is water-soluble, it has the characteristic of feeling lighter on skin. As such, it is often used in sunscreen lotions or moisturizers whose esthetic goal is a non-greasy finish [2]. The free acid is poorly soluble in water, so it is only used as its soluble salts.^[1]