Phenylbenzimidazole Sulfonic Acid

Phenylbenzimidazole Sulfonic Acid is a water-soluble UVB filter used at concentrations up to 8% in sunscreens. Clinical studies and dermatological surveillance data indicate moderate irritation potential, particularly in sensitive skin populations, with documented cases of contact dermatitis, stinging sensations, and photoallergic reactions. While generally tolerated by non-sensitive skin, patch testing has revealed a notable incidence of delayed hypersensitivity reactions, warranting caution in patients with compromised skin barriers or known sensitivities to benzimidazole derivatives. Safety Notes: Phenylbenzimidazole Sulfonic Acid (Ensulizole) is a water-soluble UVB filter primarily found in leave-on sunscreens and day moisturizers; at the low end (~0.1–0.5%) it appears in low-SPF daily facial lotions or as a secondary/booster UVB filter alongside other filters. In consumer OTC sunscreens, especially lighter/gel and water-based formats, commercial formulas commonly use ~1–3%, with high-strength consumer-available products reaching ~4% when leveraging its UVB contribution within overall SPF systems. Rinse-off products rarely include it in meaningful amounts due to limited utility versus leave-on photoprotection.