Methylisothiazolinone: An Underdiagnosed Cause of Contact Allergies

Low MI concentrations in standard tests may yield false-negative results.

Methylchloroisothiazolinone (MCI) and methylisothiazolinone (MI) are preservatives in cosmetics and personal hygiene products. These potent sensitizers can cause allergic contact dermatitis. Standard patch tests mix both agents in a single patch. However, the concentration of MI in the MCI/MI combination may be too low to identify all patients with an MI allergy (Dermatitis 2013; 24:2).

Investigators reviewed medical records of 703 patients with possible contact dermatitis who underwent patch testing with both combined MCI/MI and MI alone at a concentration higher than that used in the combination. Fifty-seven patients (8.1%) had positive reactions. The most common was positive to MI and negative to MCI/MI (60%). Thirty percent had positive …

Reviewing Author

Craig A. Elmets, MD

Disclosures

Consultant / Advisory board Astellas Pharmaceuticals

EquityVaxin

Grant / Research support NIH; NIH/NCI; Veteran’s Administration; Ferndale Laboratories; Kyowa Hakko Kirin Pharma, Inc.

Editorial boards Cancer Prevention Research; Photodermatology, Photoimmunology, & Photomedicine; UpToDate; eMedicine; Journal of Dermatological Sciences; JAMA Dermatology

Leadership positions in professional societies American Academy of Dermatology (Vice Chair, Committee on Science and Research); Photomedicine Society (Board of Directors)