Sodium Benzotriazolyl Butylphenol Sulfonate

Sodium Benzotriazolyl Butylphenol Sulfonate is a water-soluble UV filter/stabilizer used in low percentages (often ~0.5–5%) to improve photostability; it is a large, highly sulfonated molecule with limited skin penetration, which generally supports good tolerability. Available patch-test and post-market data suggest a low but non-zero risk of irritation or rare sensitization, particularly in compromised barriers (e.g., eczema) or when combined with multiple UV filters/solubilizers that can cumulatively irritate. Given the stakes for highly reactive patients, I rate it as gentle but not inert. Safety Notes: Sodium Benzotriazolyl Butylphenol Sulfonate is a water-soluble UV absorber/photostabilizer (often supplied as an aqueous solution) used at very low levels (~0.05–0.3%) in daily moisturizers/serums and many sunscreens primarily to protect formula color/fragrance and improve UV filter photostability. In high-UV, long-wear leave-on products—especially tinted/mineral-hybrid sunscreens and anti-pollution/day-shield products—commercially observed use can reach ~1–3% active to boost photostability and reduce photo-degradation of dyes and actives; rinse-off products tend to sit at the low end due to limited benefit and cost. There is no specific EU/FDA maximum limit widely codified for this stabilizer in cosmetics, so market practice and solubility/tolerance typically set the upper bound in consumer OTC products.