Terephthalylidene Dicamphor Sulfonic Acid

Terephthalylidene Dicamphor Sulfonic Acid (Ecamsule/Mexoryl SX) is a water‑soluble UVA filter typically used around 1–10% in sunscreens and has a strong clinical safety record with low rates of irritant reactions in standard patch testing and real‑world use. Because it is an acidic, sulfonated UV filter and is usually formulated in sunscreen bases that can sting on compromised or eczematous skin, a small but real irritation risk remains—especially when applied near eyes or on barrier-impaired skin—supporting a “gentle” rather than “very gentle” score. Safety Notes: Terephthalylidene Dicamphor Sulfonic Acid (ecamsule/Mexoryl SX) is primarily seen in leave-on sunscreen and daily moisturizer-with-SPF products; at the low end it appears around ~0.1–1% in multi-filter formulas where it is a supporting UVA filter. In consumer high-UVA-protection sunscreens sold in EU/Canada and other markets where it is permitted, real-world formulas commonly reach ~3–6% active to achieve strong UVA performance while maintaining photostability; rinse-off use is uncommon and typically lower when present. In the US it is generally not used in OTC sunscreens due to regulatory status, so the observed market range is driven by non-US consumer products.