Methylisothiazolinone (MIT) and its chlorinated analogue methylchloroisothiazolinone (CMIT) are synthetic biocide preservatives that became ubiquitous in cleaning products, cosmetics, and wet wipes during the 2000s and 2010s following the shift away from parabens. They proved to be potent skin sensitisers and respiratory allergens — triggering a major regulatory backlash in Europe that has restricted but not eliminated their use. MIT is now considered one of the most significant causes of epidemic contact dermatitis in modern history.
Where it's found
Rinse-off cleaning products including washing-up liquid, laundry detergents, and bathroom cleaners contain MIT as a preservative — typically at concentrations of 15 to 100 ppm. Leave-on cosmetics including moisturisers, shampoos, and baby wipes were a major sensitisation source until EU restrictions in 2016 and 2017. Wet wipes, including "natural" and baby-marketed products, remain a concern. Industrial and institutional cleaning products often contain higher concentrations than retail versions. Paints and coatings — MIT/CMIT (the Kathon CG blend) has been used as an in-can preservative in emulsion paints since the 1980s.
Routes of exposure
Skin contact is the primary sensitisation route — repeated dermal contact during cleaning, dishwashing, and use of personal care products. Once sensitised, even trace amounts of MIT in rinse-off products cause reactions. Inhalation during use of MIT-preserved sprays is an additional route, particularly relevant for occupational respiratory sensitisation. Eye contact from splash during cleaning. Residual MIT in laundry can transfer to clothes and cause chronic low-level skin contact.
Health concerns
MIT and CMIT are category 1 skin sensitisers — they provoke immune-mediated allergic contact dermatitis upon repeat exposure. After sensitisation, reactions can be triggered by minute concentrations: itching, redness, vesicles, and eczema are typical presentations. MIT sensitisation rates among dermatitis patients rose sharply during the 2000s as usage increased, peaking at around 10% of patch-test positive patients in some European clinic series. Respiratory sensitisation and occupational asthma have been documented in workers using MIT-preserved products. MIT is also a neurotoxin in cell culture and animal studies at higher concentrations, causing neuronal cell death through oxidative stress mechanisms, though in vivo relevance at domestic exposure levels is uncertain.
Evidence
Contact sensitisation by MIT and CMIT is categorically established — it underpins EU regulatory restrictions and is enshrined in dermatological patch test batteries. Respiratory sensitisation evidence is supported by occupational case series and animal inhalation studies. The scale of the contact dermatitis epidemic attributable to MIT was confirmed by European multicentre dermatitis surveillance networks (ESSCA, IVDK). Neurotoxicity at high concentrations is established in vitro but has not been confirmed at domestic exposure levels.
Who's most at risk
People with pre-existing eczema, psoriasis, or atopic dermatitis are particularly susceptible to MIT sensitisation. Healthcare workers and professional cleaners with intensive hand contact with cleaning products face elevated occupational exposure. Infants and young children whose skin barrier is less mature absorb more per unit area; baby wipes were implicated in a wave of infant contact sensitisation cases prior to regulatory action. Once sensitised, any future contact with MIT — even at trace levels — can provoke reactions.
Regulatory status
RegulationMIT is banned from leave-on cosmetics in the EU under Cosmetics Regulation (EC) 1223/2009 (since 2016) and restricted to a maximum of 0.0015% in rinse-off cosmetics (since 2017). The blend CMIT/MIT (Kathon CG) is restricted to 0.0015% in rinse-off cosmetics. There are no equivalent restrictions on MIT in cleaning products in the EU, UK, or US — concentrations in cleaning products can be substantially higher than those that caused the cosmetic dermatitis epidemic.
How to reduce your exposure
Read ingredient labels on cleaning products, laundry detergents, and wet wipes for methylisothiazolinone, methylchloroisothiazolinone, MIT, CMIT, or Kathon CG. Choose products specifically labelled preservative-free or MIT-free. Wear rubber gloves during dishwashing and general cleaning to limit skin contact. If you develop unexplained hand eczema, request a patch test including MIT/CMIT — this is now a standard inclusion in the European baseline patch test series.
The nutrition connection
The MIT contact dermatitis epidemic illustrates how regulatory gaps between cosmetics and cleaning products allow the same chemical to re-enter the exposure chain through a different product category. Improving ingredient literacy — reading labels on cleaning products with the same attention as food and personal care products — is a core Nutriofia competency. Choosing unscented, preservative-minimal cleaning products reduces the total allergen and irritant load on skin, which is particularly relevant for households with members who have inflammatory skin conditions.