Methylisothiazolinone

Methylisothiazolinone is a synthetic, water-soluble isothiazolinone preservative used in cosmetics and household products to combat microbial growth, chosen for broad-spectrum protection at very low levels, though sensitivity concerns limit its use.
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Ingredient Snapshot

Overview
A preservative that keeps formulas fresh, though it can irritate some skin.
Category
Preservative
Type
Preservative

Ingredient Ratings

Overall Rating

Poor

Comedogenic Risk

None

Skin Benefits

Helps keep formulas stable by reducing microbial spoilage, supporting product longevity, though individuals with sensitive skin may prefer to avoid it due to its higher allergy potential.

Uses In Skincare & Cosmetics

Primarily used in rinse-off formats like shampoos, body washes, and household cleaners; far less common in leave-on creams or serums.

Comedogenic Rating

This ingredient is not typically evaluated for comedogenicity, and no standardized rating is available.

Safety

Notable irritant/sensitizer; those with reactive skin should be cautious. In the EU, it's banned in leave-on cosmetics and restricted to very low levels in rinse-off products. Short contact times reduce risk but do not eliminate the chance of reactions.

Is Methylisothiazolinone a Good Ingredient?

While it's highly effective at very low doses, it has a well-documented high sensitization rate and is a frequent trigger for allergic contact dermatitis, which is why it rates Poor, especially given the elevated risk in leave-on use.

Products with Methylisothiazolinone

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