Methylisothiazolinone is a broad-spectrum preservative found in a surprisingly wide range of everyday products, from shampoos and baby wipes to house paint and laundry detergent. It works by killing bacteria and fungi, which makes it useful for keeping water-based products from spoiling on the shelf. The problem is that it also causes allergic skin reactions in a significant number of people, which is why knowing where it hides matters.
Personal Care and Hair Products
Hair products are one of the most common places you’ll encounter methylisothiazolinone. Shampoos, conditioners, detangler sprays, and combination body wash/shampoo products frequently contain it. A survey of children’s personal care products found it in 10 out of 37 hair products tested, including products from Suave, Aussie, White Rain, and store brands from Target (Up & Up) and Walmart (Equate). Body washes, liquid hand soaps, and bubble baths also use it as a preservative, though it appears less frequently in bar soaps.
Moisturizers, lotions, and sunscreens round out the personal care category. At least one Neutrogena baby sunscreen was found to contain it. The preservative also shows up in cosmetics and emulsions where water content creates conditions for microbial growth.
Wet Wipes and Baby Products
Facial and body wipes are the single product category most likely to contain methylisothiazolinone. In one survey, 14 out of 39 facial or body wipes tested positive for it, along with 2 out of 6 antibacterial hand wipes. Brands that have used it include Huggies, Kleenex Cottonelle, and store brands from Target and Walmart.
This is particularly concerning because wipes are often used on sensitive skin, on babies, and around the diaper area. Researchers documented six children in the U.S. who developed chronic eczema on their buttocks and faces from using baby wipes containing methylisothiazolinone. Their rashes didn’t respond to antibiotics or steroid creams until the wipes were identified as the cause and removed. Because wipes sit on the skin without being rinsed off, they deliver prolonged exposure to the preservative.
Household Cleaners and Detergents
Methylisothiazolinone is commonly added to household cleaning products as a substitute for formaldehyde-based preservatives. You can find it in liquid dish soap, liquid laundry detergent, all-purpose spray cleaners, and window cleaning solutions. Air fresheners, including room sprays, also use it. If you’re sensitive to this chemical, household cleaners can be a frustrating source of exposure because residue on countertops, dishes, and clothing contacts your skin repeatedly throughout the day.
Paint, Adhesives, and Industrial Products
Water-based paints are a major but often overlooked source of methylisothiazolinone. Manufacturers add it to prevent bacterial and fungal growth in the can and during application. This means freshly painted rooms can trigger reactions in sensitized individuals, both through skin contact and airborne exposure as the paint dries.
Adhesives are another category. Studies of wallpaper adhesives found methylisothiazolinone or its close relatives in roughly 86% of products tested. Food packaging adhesives have also been found to contain it. Industrial uses extend to cooling oils, cutting oils, and paper finishes. Unlike cosmetics, these industrial and household products are generally not required to list non-hazardous preservatives on their labels, making them harder to identify.
Yard Care and Pet Products
Pet shampoos, sprays, and other pet care products use methylisothiazolinone for the same reasons human products do. Yard care products, including certain herbicide and pesticide formulations, also contain it as a preservative for the liquid base. These are easy to overlook if you’re focused only on checking your bathroom products.
How to Spot It on Labels
The ingredient goes by several names. On cosmetics and personal care labels, look for methylisothiazolinone, MI, MIT, or the chemical name 2-methyl-4-isothiazolin-3-one. It’s also frequently paired with a related chemical called methylchloroisothiazolinone (MCI). This combination is sometimes listed as MCI/MI or sold under the trade name Kathon CG. If a label lists either chemical, the product contains an isothiazolinone preservative.
Cosmetics and personal care products in most countries are required to list preservatives on the label. Paints, adhesives, and cleaning products often are not, which makes avoidance harder outside the bathroom.
Regulatory Restrictions
The European Union originally allowed methylisothiazolinone in cosmetics at concentrations up to 100 parts per million. After a wave of allergic reactions, the EU’s Scientific Committee on Consumer Safety concluded that no concentration is safe in leave-on products like moisturizers and wet wipes. For rinse-off products like shampoo, the committee set a safe threshold of just 15 parts per million, a fraction of what was previously allowed. The EU subsequently banned it from leave-on cosmetics entirely.
The U.S. has no equivalent federal ban. The preservative remains legal in American personal care products at higher concentrations, though some manufacturers have voluntarily reformulated. If you’re shopping in the U.S. and want to avoid it, reading the ingredient list is your only reliable option.
What a Reaction Looks Like
Methylisothiazolinone causes allergic contact dermatitis, a delayed-type allergic reaction. The rash typically appears as red, itchy, inflamed skin in areas that contact the product. On the face and hands, it can look like chronic eczema. In children using contaminated wipes, it often shows up around the buttocks, genitals, and face. The reaction can develop gradually over weeks or months of repeated exposure, making it difficult to connect to a specific product.
Once you’re sensitized, even tiny amounts can trigger a flare. One case study documented a patient whose rash took nine months to fully clear after the offending product was removed. Patch testing by a dermatologist is the standard way to confirm the allergy. If you suspect a reaction, eliminating all products containing MI or MCI is the most effective step, and that means checking every product in your home, not just the obvious ones.