Methylisothiazolinone (MI) is a synthetic isothiazolinone preservative used in cosmetics and personal care products to prevent microbial growth. It is effective at low concentrations but is recognized as a significant contact allergen.
| Reported effect | How often | Notes |
|---|---|---|
| Allergic contact dermatitis | Common | A leading cause of preservative-related contact allergy; presents with redness, itching, and eczematous rash, often on the face, hands, or areas of product contact. |
| Skin irritation | Common | Stinging, burning, or redness, particularly in higher concentrations or in leave-on products. |
| Sensitization on repeated exposure | Common | Cumulative exposure can induce new allergy; once sensitized, reactions may occur to very low levels. |
| Airborne contact dermatitis | Uncommon | Reactions on exposed skin (face, eyelids) from volatilized MI in paints, household products, or wall coverings. |
| Photoaggravated or widespread dermatitis | Rare | Severe or generalized eczematous reactions reported in highly sensitized individuals. |
| Systemic contact dermatitis | Very rare | Rare reports of more diffuse reactions following exposure in already-sensitized patients. |
Frequencies reflect typical cosmetic use reported in the literature, not a guarantee for your skin.
Peer-reviewed papers on this ingredient, via PubMed.