Methylchloroisothiazolinone (MCI) is a synthetic isothiazolinone preservative used at very low concentrations to prevent microbial growth in cosmetics and personal care products, often combined with methylisothiazolinone. It is typically restricted to rinse-off products due to its sensitizing potential.
| Reported effect | How often | Notes |
|---|---|---|
Allergic contact dermatitis | Common | A well-recognized contact allergen; positive patch-test reactions are frequently reported in sensitized individuals. |
Skin irritation (redness, itching, burning) | Uncommon | Can occur especially in leave-on products or at higher concentrations. |
Eczematous flare or chronic dermatitis | Uncommon | Seen with repeated exposure in already sensitized people. |
Generalized or widespread dermatitis | Rare | May occur from airborne or extensive exposure in highly sensitized individuals. |
Systemic contact dermatitis | Very rare | Rarely reported following significant exposure in sensitized patients. |
Frequencies reflect typical cosmetic use reported in the literature, not a guarantee for your skin.