Benzyl Methylisothiazolinone

HIGH CONCERN — contraindicated for sensitive-skin formulations. Methylisothiazolinone triggered a documented epidemic of contact allergy in Europe in the 2010s with sensitization rates of 6–12% in dermatitis populations. EU banned from all leave-on cosmetics in 2016; still permitted in rinse-off at ≤0.0015% only. Remains permitted in leave-on products in US, Canada, and Australia — formulators should avoid in all leave-on applications globally regardless of local regulation. Sensitization rate for phenoxyethanol (preferred alternative) is 0.3–1% — 6–40x lower. Avoiding MI in leave-on products reduces both individual sensitization risk and population-level allergen burden.

Still permitted in leave-on products in the US, Canada, and Australia — no federal ban. Sensitization rate 6–12% in clinical dermatitis populations. Industry self-restriction strongly recommended for all leave-on products globally. Decline in usage has produced measurable population-level reduction in sensitization rates in EU-compliant markets.