What is Methylchloroisothiazolinone (MCI)?
Methylchloroisothiazolinone (MCI) is a potent antimicrobial preservative that has been used in cosmetics and household products since the 1970s. It is almost always used in combination with methylisothiazolinone (MI) in a mixture known as Kathon CG or MCI/MI. Together, they provide effective protection against bacteria, mould, and yeast at very low concentrations.
Because MCI is so effective at low doses, it was historically used in leave-on products like moisturisers and baby wipes. This led to a sharp rise in allergic reactions, prompting regulatory restrictions in the European Union and other regions.
Why does MCI cause reactions?
MCI is one of the most potent preservative allergens in patch test databases:
High sensitization rate: MCI/MI consistently ranks among the top preservative allergens in North American and European patch test studies. Sensitization can develop from everyday exposure to shampoos, wipes, and cleaning products.
Leave-on exposure: When MCI was allowed in leave-on products, reactions were often severe—facial dermatitis, eyelid swelling, and widespread rash. EU regulations now prohibit MCI/MI in leave-on cosmetics, but it may still appear in rinse-off products and household cleaners.
Cross-reactivity: People allergic to MCI are usually also allergic to MI when tested. If you react to one, assume both are problematic.
Cumulative exposure: MCI/MI appears in shampoos, conditioners, hand soaps, wet wipes, and cleaning sprays. Daily use across multiple products increases the risk of sensitization.
In Indian products 🇮🇳
MCI/MI may still appear in:
- Mass-market shampoos and conditioners
- Wet wipes (baby wipes, facial wipes, hand wipes)
- Liquid hand soaps and body washes
- Some household cleaning products sold for personal use
Indian regulations have moved toward restricting MCI/MI in leave-on products, but rinse-off products may still contain it. Check ingredient lists carefully, especially for products used on children or sensitive skin.
How to avoid MCI
- Read ingredient lists — Look for "Methylchloroisothiazolinone", "Methylisothiazolinone", "MCI", "MI", or "Kathon CG".
- Avoid "dirty" wipes — Wet wipes were a major source of MCI exposure. Choose wipes labeled preservative-free or with alternative preservatives.
- Check shampoo and conditioner — These are the most common cosmetic sources. Switch to MCI/MI-free options if you suspect sensitivity.
- Consider household cleaners — Hand soaps and cleaning sprays may contain MCI/MI. Wear gloves or switch to products without these preservatives.
Safer alternatives
- Phenoxyethanol — Common replacement; not without sensitivity reports but generally lower risk.
- Sodium benzoate and potassium sorbate — Mild preservatives often used in "sensitive" formulations.
- Preservative-free or self-preserving — Single-use products, anhydrous formulations, or those using alternative systems.
When to see a doctor
If you have persistent facial, hand, or body rash—especially if it worsens with product use—see a dermatologist for patch testing. Confirming MCI/MI allergy allows you to systematically eliminate exposure and choose safer products.