The Lab
Specimen No. 0199
AvoidSyntheticcosmetic preservative

Methylchloroisothiazolinone

CAS 26172-55-4 · MCI · CMIT · Methylchloroisothiazolinone

A synthetic preservative, normally blended with methylisothiazolinone, that is a potent skin sensitizer implicated in the same contact-dermatitis epidemic.

high confidence
Researched July 7, 2026

Concerns

  • The methylchloroisothiazolinone/methylisothiazolinone (MCI/MI) blend is a widely used preservative for which a considerable increase in cases of contact dermatitis has been recorded, prompting calls for stricter legislation (Leiva-Salinas 2014, PMID 24626102)
  • Tested at the older 100 ppm concentration, up to 50 percent of contact-allergy cases can go undetected, indicating a potent sensitizer that is easy to under-diagnose (Leiva-Salinas 2014, PMID 24626102)
  • MCI/MI allergy formed part of the 2010 to 2015 global epidemic that peaked in 2013 and 2014 (Ozkaya 2020, PMID 32691417)

Regulatory flags

  • IARC Class: NL
  • EDC Status: Not established
  • Regulatory: EU: restricted preservative (Annex V); US: permitted
  • Evidence Grade: A

Commonly found in

Rinse-off cosmeticsShampooWet wipesHousehold cleanersWater-based paint

Research disclaimer: This rating is based on available peer-reviewed research and regulatory assessments at the time of publication. It is not medical advice. Consult a qualified professional for personal health or skin concerns.

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