2-Phenylbenzimidazole-5-Sulfonic Acid

This chemical does not meet GHS hazard criteria for 86% (117 of 136) of all reports.

Warning

H315 (14%): Causes skin irritation [Warning Skin corrosion/irritation]

P264, P264+P265, P280, P302+P352, P305+P351+P338, P321, P332+P317, P337+P317, and P362+P364 (click each P-code to see the statement)

Aggregated GHS information provided per 136 reports by companies from 4 notifications to the ECHA C&L Inventory. Each notification may be associated with multiple companies.

Chemical: 1H-Benzimidazole-5-sulfonic acid, 2-phenyl-

REACH registered substance: 2-phenyl-1H-benzimidazole-5-sulphonic acid (EC: 248-502-0)

2-Phenylbenzimidazol-5-sulphonic acid: Does not have an individual approval but may be used under an appropriate group standard

A 2025 publication by authors in the U.S. and U.K. reviewed the toxicity and human exposure data for ensulizole as currently used in over-the-counter sunscreen formulations. The information included results from in vitro, animal toxicity, and human studies. The authors concluded that ensulizole does not pose risks to human health when used in sunscreen products at concentrations up to 4% (permitted maximum usage level in the U.S., Canada, and Australia), and that it is a Category I (generally recognized as safe and effective) UV filter under the U.S. FDA 1999 final monograph while being under current review by the FDA under over-the-counter (OTC) reform legislation.

Ensulizole strongly absorbs UV-B wavelengths. It offers protection against UV-B-induced cyclobutane pyrimidine dimers. Based on the findings in vitro and in cellulo, ensulizole induces damage on the DNA, causes DNA strand breaks and photosensitizes the formation of oxidized guanines via type I and II photosensitization mechanisms following UV-A or UV-B irradiation. Ensulizole is capable of generating reactive oxygen species, including singlet oxygen upon photoexcitation.

A 2025 review by authors in the U.S. and U.K. noted that ensulizole is a water-soluble, photostable sunscreen active ingredient. It absorbs efficiently at short ultraviolet (UV) wavelengths (i.e., UVB) and is used with other UV filters due to its minimal protection against UVA wavelengths. Also, they noted that it is more commonly found in daily use facial products (e.g. moisturizers) and rarely in recreational sunscreen products, which are often water resistant.

A 2025 review by authors in the U.S. and U.K. used experimentally determined values of 4% for oral absorption in rats and 0.26% for dermal absorption in humans for their risk calculation purposes. Also, the authors noted no evidence of bioaccumulation in rat vivo studies, which they stated is consistent with the high water solubility and low octanol/water partition coefficient.