Why does Health Canada restrict MIT and MCI preservatives?

Because the concentrations once considered safe turned out to trigger allergic contact dermatitis in a rapidly growing share of the population — so Health Canada now caps both preservatives by concentration and product type rather than banning them outright.

What do MIT and MCI actually do in a product?

They're preservatives — isothiazolinone compounds added in small amounts (parts per million) to stop bacteria, yeast, and mold from growing in water-based formulas. They're cheap, broad-spectrum, and effective at very low concentrations, which is why they became common in rinse-off products like shampoo, conditioner, and body wash starting in the 1990s (as the combination "Kathon CG," MCI+MIT) and expanded into leave-on products and MIT-only formulas in the 2000s once MCI alone drew allergy concerns.

What does Health Canada's rule actually say?

Per our ingredient database, Health Canada's Cosmetic Ingredient Hotlist lists both as restricted, not prohibited:

  • Methylisothiazolinone: "Restricted in Canadian cosmetics: not permitted in leave-on products; capped at 0.0015% in rinse-off products (a combined cap shared with methylchloroisothiazolinone when both are present in the same formulation)."
  • Methylchloroisothiazolinone: "Restricted in Canadian cosmetics: not permitted on its own — only permitted at all when combined with methylisothiazolinone (MI), and only in rinse-off products, with the combined MI + MCI concentration capped at 0.0015%."

So the honest summary is: MCI can't be used solo under any condition, MIT can be used solo but only in rinse-off products, and when either or both are present the combined concentration ceiling is the same 0.0015% (15 parts per million) either way. Nothing in the hotlist calls these ingredients banned outright — the restriction is about where and how much, not whether at all.

Why did the safe concentration change?

Not because new toxicology emerged — MIT was assessed as non-genotoxic back in 2004. What changed was the sensitization data. The EU's Scientific Committee on Consumer Safety (SCCS) reviewed MIT twice, first in 2013 (SCCS/1521/13) and again after industry submitted new data in 2015 (SCCS/1557/15, finalized December 2015). At the time, EU rules allowed MIT at up to 100 ppm (0.01%) in both leave-on and rinse-off products. Cosmetics Europe, the industry trade association, argued in its 2014 submission that 100 ppm should remain safe for rinse-off and leave-on hair products; the SCCS rejected that position both times.

The SCCS's own opinion compiled patch-test surveillance from independent contact-dermatitis research groups working in different countries, and the pattern was consistent across all of them: contact allergy to MIT rose sharply between 2010 and 2013 — researchers in the UK (Urwin & Wilkinson, 2013), Finland (Lammintausta et al., 2014), and Denmark (Lundov et al., 2013) titled their own reports on the trend an "epidemic" outright, while independent groups in Belgium (Aerts et al., 2014), France, and Germany documented the same sharp rise without using that specific word. Reactivity rates in patch-tested dermatitis patients climbed from roughly 1–2% in 2010 to 6–17% in some clinics by 2012–2013, depending on the country and patient population. A separate French network (REVIDAL-GERDA, 16 centers, nearly 8,000 patients) recorded MIT-positive patch tests rising from 1.5% in 2010 to 5.6% in 2012. The SCCS also noted that MIT had been used at concentrations up to 8.8 times higher than MCI over the preceding decade — a dosing shift that tracked with the allergy rise. Its final conclusion: 100 ppm was not safe even in rinse-off products, no safe leave-on concentration could be demonstrated at all, and 15 ppm (0.0015%) — the same figure Health Canada now uses — was the ceiling it could support for rinse-off use only.

A 2020 follow-up study across 14 European centers (Uter et al., Journal of the European Academy of Dermatology and Venereology) found MIT contact-allergy prevalence in patch-tested patients fell by about half between 2015 and 2017, after EU rules tightened, with the eliciting products shifting away from leave-on cosmetics toward rinse-off and household items — evidence the restriction did what it was meant to do, even as it shows the problem hasn't disappeared. A U.S. cohort study from the same period (Yu et al., 2016, JAMA Dermatology, single academic contact-dermatitis clinic, n=703) found MIT/MCI contact allergy in 8.1% of patch-tested patients, rising from 2.5% in 2012 to 6.8% in 2014 — the U.S. lagged behind Europe's regulatory response, which the authors used to argue for tighter American limits.

Is a rinse-off product with MIT or MCI actually risky?

For most people using a product within Health Canada's current limits, the risk is low — these are contact allergens, not systemic toxins, and allergic contact dermatitis requires prior sensitization plus re-exposure at a threshold concentration. The regulatory cap exists precisely because rinse-off exposure at 15 ppm was the concentration the SCCS could find adequate safety data for. If you've never reacted to a preservative before, that's the level regulators consider defensible. If you already have a known isothiazolinone allergy — confirmed by patch testing, not self-diagnosis — avoidance matters more than concentration, since even trace leave-on exposure (a "rinse-off" product left on skin longer than intended, or residue in a still-damp environment) can trigger a reaction in an already-sensitized person.

Where do these preservatives show up in what people actually buy?

In our catalog, MIT (methylisothiazolinone) and MCI (methylchloroisothiazolinone) turn up almost entirely in rinse-off formulas — shampoos, conditioners, and cleansers — which lines up with the regulatory picture above. Examples currently live include Dove Daily Moisture Conditioner, Aussie Miracle Curls Conditioner, Daeng Gi Meo Ri Shampoo for Normal to Dry Scalp, Bumble and Bumble Gentle Shampoo, and ACNES Foaming Wash Refill. None of these are being flagged here as unsafe — inclusion in this list reflects only that the ingredient is present, and formulation-level testing (concentration, exposure time, individual sensitivity) isn't something an ingredient list alone can tell you. If you want to check whether a specific product you own contains either preservative, our ingredient pages for methylisothiazolinone and methylchloroisothiazolinone list current regulatory status, or you can run a full label through our ingredient checker.

The bottom line

Health Canada's rule isn't a ban — it's a concentration-and-product-type restriction built directly on the SCCS's sensitization data, which itself was built on independent patch-test surveillance across multiple countries showing a real, measurable rise in contact allergy. The 0.0015% combined cap in rinse-off-only products is the number that data could support; nothing in the record justifies scarier language than that, and nothing in it justifies dismissing the restriction as excessive caution either.