Colloidal Sulfur

Colloidal sulfur is a keratolytic/antimicrobial acne and seborrheic dermatitis active typically used around ~2–10%, and it commonly causes dryness, stinging, and irritant dermatitis—especially on compromised barriers (eczema, retinoid/AHA users). Patch testing and clinical experience show irritation is not rare at therapeutic strengths and can be cumulative when layered with other actives, so it warrants a significant irritancy score for sensitive-skin safety. Safety Notes: In consumer acne and anti-blemish products, colloidal sulfur is found as a low-level supportive active around ~0.1–1% in gentle cleansers, masks, and spot products, often alongside salicylic acid or zinc. The high end of the OTC market is dominated by maximum-strength sulfur acne treatments (spot creams, lotions, and masks) at 10%, which is widely commercialized and aligns with the common OTC drug monograph limit for sulfur in acne products in the U.S. Rinse-off formats (cleansers/masks) frequently sit in the mid-range (e.g., 2–5%), while leave-on spot treatments more often reach 3–10% due to efficacy expectations and odor/irritation tradeoffs.