Is methylisothiazolinone banned?

In the EU it is prohibited in leave-on cosmetics from February 2017 and capped at 15 ppm in rinse-off products from 2018. Limits differ elsewhere, so imported leave-on products can still contain it.

Why is methylisothiazolinone a problem?

It caused a documented contact-allergy epidemic after the industry moved from the older 3:1 blend to MI alone at much higher concentrations. It was the American Contact Dermatitis Society's Allergen of the Year in 2013.

What does methylisothiazolinone cross-react with?

Methylchloroisothiazolinone and benzisothiazolinone — the latter is widely used in cleaners, laundry products and paint, so sensitisation reaches well beyond cosmetics.

Is it safe in a rinse-off product?

At the current EU limit of 15 ppm it is acceptable for most people in something that washes off in seconds. Anyone already sensitised should avoid it entirely.

Why were wet wipes singled out?

They were a leave-on product used repeatedly, often on broken or irritated skin — the conditions under which sensitisation is most likely.

Methylisothiazolinone — Ingredient Guide

How it works

Methylisothiazolinone — MI, or MIT — is a preservative from the isothiazolinone family. It kills bacteria and fungi by reacting with thiol groups in their proteins, which is fast, broad and effective at very low levels. It is also, unfortunately, a mechanism that does not distinguish between a microbe's proteins and yours, which is the root of everything below.

It arrived as a replacement. For years it was used only in a 3:1 blend with methylchloroisothiazolinone, sold as Kathon CG, and when that blend's allergy rate became a problem the industry moved to MI alone — at concentrations up to twenty-five times higher than it had been used in the blend.

The evidence

What followed is the best-documented contact-allergy epidemic in modern cosmetic history. Patch-test clinics across Europe recorded sensitisation rates climbing through the early 2010s, and the American Contact Dermatitis Society named methylisothiazolinone its Allergen of the Year in 2013. Wet wipes were a particular problem: a leave-on product, applied repeatedly, often to broken or irritated skin.

The EU response was unusually decisive. Regulation (EU) 2016/1198 banned MI in leave-on cosmetics outright from February 2017, on the finding that no safe concentration for inducing contact allergy had been demonstrated. Regulation (EU) 2017/1224 then cut the rinse-off limit to 15 ppm from 2018 — a level low enough that MI no longer preserves the finished product at all, and now mainly reflects raw materials that arrived already preserved.

Suitability

Anyone: acceptable at the current rinse-off limit in a product that washes off in seconds
Already sensitised: avoid entirely, including the cross-reacting relatives below
Eczema-prone or broken skin: the population in which sensitisation was highest

Concentration

In the EU, prohibited in leave-on products and capped at 15 ppm (0.0015%) in rinse-off. Outside the EU the limits differ, so an imported leave-on product can still contain it at levels Europe no longer permits.

Conflicts & combinations

The cross-reaction matters more than any layering rule. MI cross-reacts with methylchloroisothiazolinone and with benzisothiazolinone, which is widely used in household cleaners, laundry products and paint — so a person sensitised by a cosmetic can go on reacting to things that are not cosmetics at all. Anyone patch-test positive to MI needs to read detergent labels, not just skincare ones.