Methylchloroisothiazolinone and Methylisothiazolinone
Methylchloroisothiazolinone and Methylisothiazolinone (MCI/MI) is a widely used blend of preservatives that effectively inhibits the growth of bacteria, yeasts, and molds in water-based cosmetic and personal care products. This combination is highly effective at low concentrations, ensuring product integrity and safety. However, it is a known sensitizer and its use is highly regulated.
Preservative blendVegan
RiskSerious 3.5 / 4
Sensitization i4 / 4
Risk of allergic contact dermatitis or immune-based reactions. Fragrance allergens, preservatives, botanicals, and some dyes may score here.
Irritation i3 / 4
Risk of short-term irritation — stinging, burning, dryness, redness, or discomfort. Common for strong actives, acids, retinoids, fragrances, and harsh surfactants.
Rated by SpottyLabs' ingredient methodology, independent of brands.
Things to watch
- High potential for skin sensitization and allergic contact dermatitis
- Can cause irritation, especially in leave-on products
- Strictly regulated and restricted in many cosmetic applications due to sensitization concerns
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Frequently asked questions
- What is Methylchloroisothiazolinone and Methylisothiazolinone?
- This is a blend of two potent preservatives, MCI and MI, used together to protect cosmetic products from microbial contamination by bacteria, yeast, and mold. It is very effective at preventing product spoilage.
- Are MCI/MI preservatives safe for skin?
- MCI/MI is a well-known contact allergen and sensitizer. Due to its high potential to cause allergic reactions, its use is heavily restricted, especially in leave-on products, and it is generally recommended to avoid prolonged skin contact.
