Sulfur

Sulfur is a keratolytic/antimicrobial acne and seborrheic dermatitis active typically used around ~2–10% in leave-on products and higher in short-contact preparations, where dryness, peeling, stinging, and erythema are common—especially on compromised or eczematous skin. Clinical experience and patch-testing data support that it is not merely “gentle” despite being common in OTC treatments, and cumulative barrier stress (often alongside retinoids/acids/benzoyl peroxide) increases irritancy risk. Given its frequent, clinically meaningful irritation in sensitive populations, it warrants a significant irritancy score. Safety Notes: In consumer skincare, sulfur is found at very low levels (~0.1–0.5%) in gentle leave-on spot treatments, masks, and cleansers where it supports oil-control/deodorizing and blemish care with reduced odor/irritation. Typical OTC acne products commonly use 2–5% sulfur, and the strongest widely available consumer formulations reach 10% sulfur (the upper end commonly seen for OTC acne treatments in the US and aligned with long-standing monograph use). Rinse-off products may use similar or slightly higher apparent loadings for performance but practical limits (odor, grittiness, instability) usually keep marketed consumer skincare at or below 10%.