{"title":"Methylisothiazolinone","entity_type":"Ingredient","slug":"methylisothiazolinone","canonical_url":"https://skinknowledgebase.com/ingredients/methylisothiazolinone","dates":{"date_modified":"2026-05-27","date_reviewed":"2026-05-27"},"mcp_eligible":true,"summary":"Methylisothiazolinone skincare benefits, mechanism, evidence limits, INCI context, and tolerability guidance for realistic dry, sensitive, acne-prone, or","evidence_sources":[],"product_fact_sources":[],"related_entities":[{"title":"Preservative Allergic Contact Dermatitis","url":"https://skinknowledgebase.com/side-effects/preservative-allergic-contact-dermatitis"}],"body_sections":[{"heading":"Quick Summary","paragraphs":["Methylisothiazolinone is a skincare ingredient used for skin sensitivity routines. It is best judged by formula context, concentration, frequency, and skin tolerance rather than by the ingredient name alone."]},{"heading":"What It Is","paragraphs":["Methylisothiazolinone is used in leave-on or rinse-off cosmetic formulas depending on the product type. In SKB it is framed as a cosmetic skincare ingredient, not a prescription treatment or a diagnosis tool."]},{"heading":"Mechanism","paragraphs":["Methylisothiazolinone is a preservative used to inhibit microbial growth in water-containing products. For users who become allergic, the relevant mechanism is delayed-type contact allergy, so persistent rash patterns need avoidance and patch-test guidance.","The mechanism is practical, not magical: vehicle, pH where relevant, dose, frequency, and the rest of the routine decide whether the ingredient feels helpful or irritating. Results should be judged gradually, and sensitive users should introduce it separately from other strong actives."]}],"side_effects":[{"title":"Preservative Allergic Contact Dermatitis","url":"https://skinknowledgebase.com/side-effects/preservative-allergic-contact-dermatitis"}]}