METHYLISOTHIAZOLINONE

EU max concentration: 0.0015% (of a mixture in the ratio 3:1 of 5-Chloro-2-methyl-isothiazol-3(2H)-one and 2-Methylisothiazol-3(2H)-one

📊 Comedogenicity

📚 Research & Evidence

🔬 The Science

Methylisothiazolinone is a preservative chemical added to cosmetics and personal care products to prevent bacterial and fungal growth. Here’s what the research shows:

#1: Rising concern and prevalence — MI became the American Contact Dermatitis Society’s Contact Allergen of the Year in 2013, signaling growing recognition of allergic reactions tied to this ingredient (Dermatitis, 2013). In Europe, approximately 1.5% of the population shows contact allergy to MI (Dermatitis, 2013). In a Bangkok dermatology clinic, researchers documented a steep rise in MI-related contact allergy, climbing from 4.8% in 2009 to 22% by mid-2014 (Dermatitis, 2015). This pattern was described as an “epidemic” of allergic contact dermatitis linked to MI (Cutis, 2019; Actas Dermosifiliogr, 2014).

#2: Detection challenges — One critical issue is that standard patch tests combining methylchloroisothiazolinone (MCI) with MI often fail to catch people allergic to MI alone. The MCI/MI combination test misses approximately 40% of true MI allergies, likely because the test concentration of MI within the mixture is too low (Dermatitis, 2013). In one study, 27.3% of patients with confirmed MI allergy actually tested negative to the standard MCI/MI combination test (Dermatitis, 2015). This means some people may not realize they’re allergic to MI unless dermatologists specifically test for it separately. #3: Broader sources of exposure — While personal care products are the most common source of MI contact allergy, this ingredient also appears in household products, industrial chemicals, paints, slime, and adhesive agents (Cutis, 2019).

Related isothiazolinone chemicals (like benzisothiazoline and octylisothiazolinone) are found in leather products, glues, industrial chemicals, and cleaning products. There may be cross-reactivity between some of these related compounds. #4: Regulatory response — Recognizing the rise in MI allergies, some countries have implemented regulations. Thailand’s Ministry of Public Health restricted MCI/MI use in cosmetics, though post-regulation surveys found these ingredients still present on product labels in various categories (Contact Dermatitis, 2019). In Europe, MI at higher test concentrations (2000 ppm) was added to baseline patch test series to improve detection (Actas Dermosifiliogr, 2014). The sources note that clinical presentations of MI allergy vary widely and diagnosis is often missed—a significant gap in current practice, particularly in the United States where the true prevalence remains unknown (Dermatitis, 2013).

💧 Skin Type Compatibility

Derived from this ingredient’s irritancy potential and comedogenicity rating against the needs of each skin type — e.g. oily and acne-prone skin are marked down for pore-clogging ingredients, sensitive skin for irritants. A starting heuristic, not a dermatological verdict.

⚠️ Don’t Combine With

🧴 Products Containing METHYLISOTHIAZOLINONE

• Nivea Men NIVEA Men Active Energy Hydraterende Dagcrème
• Nivea Lait corps sous la douche nourissant
• herbal essences champu
• H&S Champú
• AgeDefy, P&G, Pantène, Pantène Pro-V, Pantène Pro-V Expert, Pantène Pro-V Expert Collection, Procter & Gamble AgeDefy Shampooing
• AgeDefy, P&G, Pantène, Pantène Pro-V, Pantène Pro-V Expert Collection, Pantène Pro-V expert, Procter & Gamble AgeDefy soin après-shampoing
• Head & shoulders 2 in 1 Classic
• Head & Shoulders Shampooing antipelliculaire + après-shampooing 2 in 1 Sensitive
• Cien Cien Gel de baño Zero
• Head & Shoulders Shampooing antipelliculaire + après-shampooing 2 in 1 anti-chute
• h
• Head & Shoulders Shampooing antipelliculaire Instant Relief Apaisement
• Head & Shoulders Shampooing antipelliculaire Instant Apaisement
• Head & Shoulders Shampooing antipelliculaire Lisse & Soyeux (maxi pack)
• Head & Shoulders Shampooing antipelliculaire anti-démangeaisons eucalyptus (maxi pack)
• Head & Shoulders Shampooing antipelliculaire + après-shampooing 2 in 1 Menthol Fresh
• Head & Shoulders Shampooing antipelliculaire Citrus Fresh
• Head & Shoulders Shampooing antipelliculaire Sensitive
• Pantene, Procter & Gamble srl Pantene Pro-V 3 in 1 Shampoo + Balsamo + trattamento
• Protane Argan Oil of Morocco

📄 Related Research

Matched by search — not necessarily verified support for every statement above.

• Castanedo-Tardana MP et al. (2013). Methylisothiazolinone. Dermatitis.
• Sukakul T et al. (2019). Methylchloroisothiazolinone and/or methylisothiazolinone in cosmetic products-A market survey. Contact Dermatitis.
• Reeder M et al. (2019). Methylisothiazolinone and isothiazolinone allergy. Cutis.
• Puangpet P et al. (2015). Methylchloroisothiazolinone/Methylisothiazolinone and methylisothiazolinone allergy. Dermatitis.
• Leiva-Salinas M et al. (2014). Update on allergic contact dermatitis due to methylchloroisothiazolinone/methylisothiazolinone and methylisothiazolinone. Actas Dermosifiliogr.