Get a Free 5ml Mini Now Free 5ml Mini With Every Order of The Mantle
Moumoujus

METHYLISOTHIAZOLINONE.

Avoid CAS 2682-20-4 / PRESERVATIVE

Methylisothiazolinone is a powerful broad-spectrum biocide and preservative, highly effective at inhibiting the growth of bacteria, yeasts, and fungi in cosmetic formulations. However, its significant potential for skin sensitization and allergic contact dermatitis has led to severe restrictions and cautionary use in skincare.

Summary

preservative

Science

Mechanism of Action

This ingredient functions as a preservative through its electrophilic sulfur atom, which reacts with nucleophiles to disrupt vital enzymes and other proteins within microbial cells, thus preventing their proliferation. Studies also suggest its involvement in downregulating FAK tyrosine phosphorylation, contributing to its cytotoxic effects against microorganisms.

Research

Clinical Evidence

High confidence
Effective range N/A
Optimal

N/A

Key findings

  1. 01 Consistently produced sensitization in an open epicutaneous test.
  2. 02 Effective concentration inducing a stimulation index (EC3) in a local lymph node assay (LLNA) when diluted in acetone/olive oil, indicative of sensitization potential.
  3. 03 EC3 in an LLNA, demonstrating sensitization potential.
  4. 04 Elicitation concentration, capable of triggering contact dermatitis in individuals already sensitized to MI.
  5. 05 Concentration below which MI has generally not acted as a contact sensitizer in animal and human studies (for induction).

Transparency

Dusting Analysis

Commonly dusted
Min. effective
Elicitation of contact dermatitis occurs at 5 ppm (0.0005%) in sensitized individuals. For induction, concentrations below 600 ppm (0.06%) are generally considered non-sensitizing.%
Red flag below
Any detectable amount in leave-on products due to the lack of a proven safe concentration. For rinse-off products, concentrations exceeding 0.0015% (15 ppm) are a red flag.%

Methylisothiazolinone's high sensitizing capacity means that even extremely low concentrations can trigger allergic reactions in previously sensitized individuals. Regulatory bodies have set very strict limits, with the European SCCS finding no adequately demonstrated safe concentration for MI in leave-on formulations, highlighting its high risk profile despite typically low inclusion rates.

The Formula

Formulation

Solubility
Water
Optimal pH N/A
0 7 14

Stability

Methylisothiazolinone is readily photolyzed by UV radiation. While its exact optimal pH is not specified, related isothiazolinones exhibit increased degradation rates as pH rises (e.g., from 4.5 to 11), suggesting better stability in acidic conditions.

Conflicts

  • Should not be added to cosmetic products that already contain Methylchloroisothiazolinone/Methylisothiazolinone (MCI/MI) mixtures.

Safety

Safety Profile

CIR Status
Safe with restrictions
Max tested
0.0015%
Sensitization risk High

The European Union's Scientific Committee on Consumer Safety (SCCS) concluded that for leave-on cosmetic products, no safe concentration for Methylisothiazolinone has been adequately demonstrated for the induction or elicitation of contact allergy. For rinse-off products, SCCS considers concentrations up to 0.0015% (15 ppm) safe concerning induction of contact allergy. The CIR Expert Panel also concluded it is safe with restrictions, allowing up to 0.01% for rinse-off and permitting leave-on products if formulated to be non-sensitizing based on a quantitative risk assessment. The FDA classifies related isothiazolinones as chemical allergens, recognizing MI's strong association with allergic reactions.

Your Skin

Skin Compatibility

No Normal
No Dry
No Oily
No Sensitive
Irritancy High
Comedogenicity Unknown

Our Assessment

Verdict

Avoid

Despite its efficacy as a broad-spectrum preservative, Methylisothiazolinone carries a high risk of skin sensitization and allergic reactions, with no demonstrated safe concentration for leave-on products by leading European authorities, making it generally unsuitable for precision skincare formulations.

Related

Similar Ingredients

Finding similar ingredients…