Methylisothiazolinone: An Underdiagnosed Cause of Contact Allergies

Summary and Comment |
November 16, 2015

Methylisothiazolinone: An Underdiagnosed Cause of Contact Allergies

  1. Craig A. Elmets, MD

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

  1. Craig A. Elmets, MD

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 reactions to both MCI/MI and MI. A positive reaction to MCI/MI and a negative reaction to MI was least common (<10%). Dermatitis reactions were most frequent on the hands, followed by the face and extremities. Reactions in the groin or buttocks, trunk, axilla, and feet were also observed, as was disseminated dermatitis. Seventy percent of patients had been using products containing MCI/MI or MI. Nearly 75% improved when such products were discontinued.


Allergic contact dermatitis from MCI and MI is an increasing problem. In fact, MI was named contact allergen of the year in 2013. MCI and MI are found in wet wipes, shampoos, detergents, and spray-on tanners, and can be an occupational hazard for day care workers, hairdressers, and others. MCI and MI have been reported to cause contact allergies in machinists, mechanics, and workers exposed to paints and glues. This study demonstrates that MI concentrations in standard patch test series may yield false-negative results. Therefore, physicians should consider allergic contact dermatitis to MI, even if patch testing to MCI/MI on standard series is negative.

Editor Disclosures at Time of Publication

  • Disclosures for Craig A. Elmets, MD at time of publication Consultant / Advisory board Astellas Pharmaceuticals Equity Vaxin 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)


Reader Comments (2)

Monica Houghton

I think the US is far behind in regulation of this chemical. i was found to be allergic in 2013 by the T.R.U.E. test (lower concentration of combined MCI/MI) after suffering a full body rash from a detergent that was used in my washing machine for a load just prior to mine. I react even at low concentrations and with rinse off products - such as shampoo, handwash, conditioner, dish detergent. I can't even use plates/glasses that have been washed with MI and rinsed. This is a horrible allergy, and something must be done to remove this chemical from products immediately. Dry skin should not be covered with lotion - the patient should be tested for this allergy. I am positive that many cases of eczema, psoriasis, and dandruff are just a symptom of this allergy. We need to treat the cause, not the symptom - and the only treatment for this is excluding it from your daily environment, which at this point in time is near impossible.

Jack N. Moss Other, Dermatology, independent contractor

Of the mci/mi +ve subjects how many were patch +ve to other haptens,e.g. formaldehyde, fragrances, ? Since mci is used(or should be) in rinse-off products only, how many subjects showed allergic responses to shampoos, conditioners, etc.

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