By Abby S. Van Voorhees, MD, April 02, 2013
Dr. Van Voorhees: Is methylisothiazolinone (MI) a new compound? Why are we first seeing this sensitizer come on the radar now?
Dr. Zug: It’s not an entirely new compound, but the use of it on its own as a preservative in personal care products, rather than in combination with methylchloroisothiazolinone (MCI), is something new that’s happened in the last few years. The use of MI in cosmetics and toiletry products has markedly increased since introduction about five years ago. It’s been used in industrial products since the early 2000s.
Dr. Van Voorhees: How much of a problem is MI? How frequently does it cause contact sensitization?
Dr. Zug: We’re not sure of the answer yet. In Europe, the prevalence in contact dermatitis clinics is about 1.5 percent of the population that’s tested. That’s pretty typical for their population for preservatives. Historically our frequency of positives for a number of preservatives is much higher, for reasons that are not clear. It’s debated by experts in the field, but it’s not known whether our products use more preservatives or the concentrations are higher or if there is some other explanation. In the combination MCI/MI, the allowed concentration for leave-on products is 7.5 ppm and for rinse- off products 15 ppm and that is a 3:1 combination preservative. That’s a maximum of 3.75 ppm allowed of MI in that combination. However, MI is being used alone with an allowed concentration up to 100 ppm. It’s unclear how much of a problem that may be in terms of contact allergy; it is still a very low concentration that for the majority of individuals is not enough to cause sensitization. However, when used on damaged skin, such as in dermatitis, or sunburn, or thin skin such as the genitalia, that may allow for lower concentrations to result in sensitization. [pagebreak]
Dr. Van Voorhees: What are the sources for exposure to MI? When should you consider MI as the cause of a dermatitis?
Dr. Zug: You should think of it primarily when a person has a facial dermatitis, a perianal or genital dermatitis, a chronic eczematous dermatitis when something with MI is or has been used, and in some instances a hand dermatitis.
Dr. Van Voorhees: Is it mostly from cosmetics? Are there occupational exposures as well?
Dr. Zug: Cosmetics and toiletries, yes. The real hidden source has been baby wipes since patients don’t often mention their use and we may omit asking. In two of my patients I suspected a sunscreen allergy and they were actually allergic to the MI in their sunscreen. To my surprise, some of the sunscreens that I’ve always recommended to people because of low frequency of allergy in those brands have incorporated MI into their formulations. It’s also commonly used in products like lotions and creams.
Dr. Van Voorhees: Are there also household products that contain MI?
Dr. Zug: There are household products with MI in them. The problem with household products is there are no labeling requirements for ingredients, so it can be difficult to find out what is in household cleansers and dish liquids. You can find labeling information online for some products. To our surprise, we found that there’s a very popular green product that has MI incorporated as its preservative. [pagebreak]
Dr. Van Voorhees: How about occupational exposures? Is this seen in that setting as well?
Dr. Zug: I think the primary occupational exposure is from paint, so people should think about it in painters. It can cause an airborne distribution of dermatitis. It has also been reported in carpet glue. You should also consider it for people in occupations where you’d typically be worried about preservative allergies: food handlers, people in health care, and machinists. People who have to wash their hands a lot.
Dr. Van Voorhees: How does one screen for MI? Is it part of the standard patch test series?
Dr. Zug: The current test is for MCI and MI in combination and, because of the low concentration of MI in that mix (25ppm in the MCI/MI mix of 100ppm), MCI/MI tested at 100ppm is not considered an adequate screen for MI allergy. It misses between 30 and 60 percent of patients who are actually allergic to MI. A good screen is not currently a part of any standard series.
Dr. Van Voorhees: In the absence of a standard test, what can dermatologists do to determine if MI allergy is the culprit in their patients’ contact dermatitis?
Dr. Zug: One thing for testing is, if you have a leave-on product that can be tested as-is and contains MI, that’s one sort of test that could be done. MI can also be purchased from commercial allergen suppliers. It’s not clear what the right concentration for testing is; it may be somewhere between 1,000 and 2,000 parts per million. Most of the work on this has been done in Denmark, Finland, and Germany. [pagebreak]
Dr. Van Voorhees: Are there any pearls you can share with us about when to have a sixth sense that this is the causative agent of an eruption?
Dr. Zug: It’s when you have someone with a dermatitis that’s not resolving in one of those locations, the face, hands, or perianal and genital area, who uses products that contain MI. Remember to ask about the use of personal care wipes and baby wipes. That exposure has actually led to several cases of a pseudolymphomatous contact dermatitis occurring in the perianal and genital region. We had a patient who had localized radiation for clonality positive localized cutaneous T-cell lymphoma, then had a biopsy that looked like recurrence of the CTCL soon after treatment; he was using baby wipes containing MI. The pseudolymphomatous rash cleared with discontinuation of the wipes.
Dr. Van Voorhees: Why was MI chosen as the contact allergen of the year?
Dr. Zug: The contact allergen of the year is usually an allergen that catches our attention and needs to be recognized. The reason here is that MI is a known allergen that’s not being picked up by a standard screening series. And it’s being missed. It’s being used in a different way now, alone, and at much higher concentration than in the MCI/MI mix, which I think is going to lead to much more allergy. Europeans have exposed this very well. If you’re not looking for it, if you are not testing for it, you’re probably missing it.
Dr. Zug is professor in the section of dermatology, department of surgery and director of the dermatology residency program at Geisel School of Medicine at Dartmouth and Dartmouth-Hitchcock Medical Center. Dr. Mari Paz Castanedo Tardan is a second year dermatology resident in the Dartmouth residency program. Dr. Zug and Dr. Castanedo-Tardan’s co-authored article was published in Dermatitis, 2013; 24(1):2-6. doi: 10.1097/DER.0b013e31827edc73.