Ingredient
Methylchloroisothiazolinone
Methylchloroisothiazolinone is flagged for general use, pregnancy, breastfeeding, postpartum and PCOS. The concern behind the strongest flag is common allergen and irritant.
- MCI
- 5-Chloro-2-methyl-4-isothiazolin-3-one
Verdict by profile
Truva checks every ingredient against six profiles. Jump to any of them for the full assessment.
- Strongest verdict
- Not Recommended
- Its verdict for general use, the profile this one is worst in
- Profiles flagged
- 5 of 6
- Counting avoid, high risk and medium risk
- Irritancy
- 4 of 5
- Higher means more likely to sting or redden
Methylchloroisothiazolinone and pregnancy
Caution Advised
- Common allergen
- Irritant
Methylchloroisothiazolinone is a preservative that prevents microbial contamination in cosmetic products. It's effective at low concentrations but has become controversial due to allergy concerns. While there are no specific reproductive toxicity concerns with MCI, pregnancy increases skin sensitivity for many women. The SCCS has identified MCI as a potent contact allergen, and pregnant women may be more susceptible to developing allergic reactions or irritation. The primary concern is skin sensitization rather than fetal harm. The EU has banned MCI in leave-on products and severely restricted it in rinse-off products due to allergenicity. While ACOG has not specifically addressed this preservative, dermatologists generally recommend that pregnant women with sensitive skin or existing allergies avoid products with MCI when possible.
Methylchloroisothiazolinone and breastfeeding
Caution Advised
- Common allergen
- Irritant
Methylchloroisothiazolinone is a preservative with known sensitizing properties. It's used in rinse-off products at very low concentrations to prevent contamination. The primary concern for breastfeeding mothers is skin irritation and allergic contact dermatitis rather than transfer to breast milk. However, if products containing MCI are applied to the breast area, there is potential for infant exposure through skin contact. The SCCS notes that MCI can cause sensitization with repeated exposure. While systemic absorption is minimal, dermatologists recommend avoiding MCI-containing products on or near the breast area during breastfeeding. The AAD recognizes MCI as a common allergen and suggests alternative preservatives for individuals with sensitive skin or allergy concerns.
Methylchloroisothiazolinone and postpartum
Caution Advised
- Common allergen
- Irritant
Methylchloroisothiazolinone is a preservative that can cause allergic contact dermatitis and skin sensitization. Postpartum hormonal changes can make skin more reactive. Women experiencing postpartum skin sensitivity should be cautious with MCI-containing products. The ingredient is a known allergen that can trigger or worsen skin conditions like eczema or dermatitis, which may already be affected by hormonal fluctuations after childbirth.
Methylchloroisothiazolinone and trying to conceive
Safe to Use
- Common allergen
Methylchloroisothiazolinone is a preservative with known allergenic properties but no evidence of affecting fertility or reproductive hormones. It remains on the skin surface with minimal systemic absorption. There are no fertility concerns associated with MCI. The primary risk is skin sensitization rather than reproductive effects. Women trying to conceive can use products with MCI, though those with sensitive skin may want to choose alternatives.
Methylchloroisothiazolinone and PCOS
Caution Advised
- Common allergen
- Irritant
- Can inflame skin
Methylchloroisothiazolinone is a preservative known for causing allergic reactions and skin sensitization. It has no hormonal effects but can trigger inflammatory responses in sensitive individuals. Women with PCOS often have more reactive or acne-prone skin due to hormonal imbalances. MCI can exacerbate skin inflammation and may worsen existing skin conditions. The SCCS has established that MCI causes contact allergy in a significant portion of the population. While MCI does not affect androgen levels or insulin sensitivity, the inflammatory response it can trigger may not be ideal for PCOS-related skin issues. Many dermatologists recommend avoiding known allergens like MCI when managing hormonal acne or sensitive skin.
Methylchloroisothiazolinone and general use
Not Recommended
- Common allergen
- Irritant
Methylchloroisothiazolinone is an effective preservative that prevents bacterial and fungal contamination in cosmetics. However, it has become one of the most problematic allergens in personal care products. The SCCS identifies MCI as a potent contact allergen responsible for a significant number of allergic reactions. Studies show approximately 3-4% of the general population develops sensitization to MCI. The American Contact Dermatitis Society named it Allergen of the Year in 2013. Repeated exposure increases the risk of developing allergy, which can be permanent once established. The EU banned MCI in leave-on products in 2016 and restricted it to 0.0015% in rinse-off products due to safety concerns. It remains legal in the US but many manufacturers are reformulating to avoid it. The SCCS recommends avoiding MCI when possible, particularly for individuals with sensitive skin or existing allergies.
Everything else flagged for the same profiles
Related ingredients
Ingredients suggested in place of Methylchloroisothiazolinone, each one with its own page here.
Ingredients that raise the same concerns.
Where this came from
Truva summarises published guidance from bodies including ACOG, the FDA, the EU SCCS and the Cosmetic Ingredient Review. It has no access to your medical history and it is not a substitute for your doctor, dermatologist or midwife. These assessments have not been reviewed by a clinician, and nothing here is a diagnosis or a prescription. If you are pregnant, breastfeeding or being treated for PCOS, take the ingredient list to the person looking after you.
Assessment last pulled from the ingredient database on .
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