Methylchloroisothiazolinone — Allergy Risk & Safety Profile

Name: Is Methylchloroisothiazolinone Safe? Allergy Risk & Alternatives
Creator: SkinDetekt

INCI: METHYLCHLOROISOTHIAZOLINONE

Also known as: MCI, Kathon CG (with MI)

🔴 High Risk

Key Facts

CAS Number: 26172-55-4
Category: preservative
Risk Level: high
Common Allergen: Yes
EU Status: Restricted
Max Concentration: 0.0015% (MCI/MI mix, rinse-off only)
Found In: shampoo, body wash

Is Methylchloroisothiazolinone safe in cosmetics?

Methylchloroisothiazolinone is rated high risk in cosmetic products. It is a known allergen that can cause contact dermatitis in sensitized individuals. Strong sensitizer, always used in combination with MI. This ingredient is restricted under EU cosmetic regulations. Safer alternatives include Phenoxyethanol, Sodium Benzoate, Potassium Sorbate. Commonly found in shampoo, body wash.

What is Methylchloroisothiazolinone?

Preservative usually paired with MI. Potent sensitizer.

Allergy & Safety Information

Methylchloroisothiazolinone is classified as a high-risk ingredient. It is a known cause of allergic contact dermatitis. It is restricted or regulated in the EU. Individuals with sensitive skin or a history of contact allergies should avoid products containing this ingredient. A patch test is recommended before first use of any product containing Methylchloroisothiazolinone.

This ingredient is classified as high risk from an allergenicity perspective. It is a recognised cause of allergic contact dermatitis with a relatively high sensitisation rate in patch-tested populations. People with a history of skin reactions to cosmetics, or with conditions such as eczema or sensitive skin, should exercise particular caution.

Allergen Note: Strong sensitizer, always used in combination with MI.

About Preservative Ingredients

Preservatives prevent microbial growth in water-containing cosmetic formulas. Without them, products would spoil within days. However, preservatives are among the most common causes of allergic contact dermatitis — they must be present in high enough concentrations to be effective, yet that same efficacy can irritate sensitised skin.

Relevance for Methylchloroisothiazolinone: If you react to one preservative, you may be cross-reactive to others in the same chemical family (e.g., isothiazolinones, formaldehyde releasers, or parabens). Checking the full preservative profile of every product you use is the most reliable way to identify your personal trigger.

How to Identify Methylchloroisothiazolinone in Products

Cosmetic ingredients are listed by their INCI (International Nomenclature of Cosmetic Ingredients) name in descending order of concentration. To check whether a product contains Methylchloroisothiazolinone, scan the ingredient list for its INCI name exactly as it appears above. Ingredients present at 1% or less may appear in any order after the 1% threshold.

Product types to prioritise checking: Shampoo, Body wash. These product categories are the most common sources of Methylchloroisothiazolinone exposure based on formulation data.

Not sure if your products contain Methylchloroisothiazolinone? Paste the ingredient list into the free ingredient checker to scan for Methylchloroisothiazolinone and other allergens automatically.