Methylisothiazolinone and Isothiazolinone Allergy
Methylisothiazolinone (MI) is a preservative commonly used in water-based personal care products. Increases in the allowable concentration of MI alone in these products has led to an epidemic of allergic contact dermatitis (ACD). Although personal care products are the most common source of MI contact allergy, other novel exposures include household products, industrial chemicals, paint, slime, and adhesive agents. Other isothiazolinones such as benzisothiazoline (BIT) and octylisothiazolinone (OIT) are uncommon in personal care products but have been found in leather products, glue, industrial chemicals, paints, and cleaning products. There may be cross-reactivity between OIT and MI, and a minority of patients who are allergic to MI are cosensitized to BIT. In this article, we review MI and related isothiazolinone chemicals.
Practice Points
- Methylisothiazolinone (MI) is a preservative found in water-based personal care products and is a common allergen in patch-tested populations.
- Methylisothiazolinone also has been identified in household products, industrial chemicals, paint, adhesives, and other unique sources.
- Benzisothiazolinone and octylisothiazolinone are structurally similar to MI, and a subset of MI-allergic patients may need to avoid them.
Household products represent an important source of MI exposure. A chemical analysis of water-based paints identified the presence of isothiazolinones. Contact allergy from isothiazolinones in paint can present as either direct or airborne-pattern contact dermatitis.11 Sodium bisulfite has been used to inactivate MCI/MI in wall paint and could be utilized in severe cases of airborne contact dermatitis.12 Off-gassing may take up to 5.5 weeks before the paint cures and the isothiazolinone level decreases.13 A 2016 analysis of household products in the CAMP database revealed that MI commonly was found in dishwashing soap (64%), followed by household cleaners (47%), laundry softeners/additives (30%), surface disinfectants (27%), and laundry detergents (13%).10 Because certain chemical ingredients are not always listed on household product labels, patients with MI contact allergy may be at higher risk for unanticipated exposure to this allergen.
Dear reader, we know that you know all of this. We know that you have been watching the MI epidemic and have followed its every turn. But something that may be new to you are the unique MI exposures identified over the last several years.
,In 2017, MI was identified in the glue used to affix 3 layers of the upper portion of a shoe.14 In addition, a recent chemical analysis of US consumer adhesives confirmed the presence of isothiazolinones in 50% (19/38) of products; 44.7% (17/38) specifically contained MI.15 Slime, the sticky play substance that children concoct out of household materials, has caused ACD, and not surprisingly, MI has been identified as a culprit allergen. In one case report, contact allergy was caused by MI present in a slime mixture made up of laundry detergent, dish soap, shampoo, and hand cream.16 In another case series, 3 children with MI contact allergy had played with slime that included dishwashing liquid, which contained MI, along with polyvinyl acetate glue and liquid soap components.17 Another case report documented slime made from MI-containing school glue as the source of ACD.18 Isothiazolinones also have been identified as causative allergens in “noise putty,” another homemade play item.19
Additionally, there has been a report of contact allergy to MI in a designer eyeglass frame.20 There also have been several documented cases of ACD to MCI/MI aerosolized from water used during ironing.21,22
There also have been several reports of photoaggravated ACD and possible photoallergic contact dermatitis from MI.23,24 In such cases, patients also may have transient photosensitivity even when MI exposure is discontinued; therefore, MI should be considered for inclusion in photopatch test panels when relevant.
Methylisothiazolinone contact allergy also should be considered for products that do not list MI on the label, which presents another potential exposure. In products that do not list MI as an ingredient on the label, its presence may be due to inclusion of the preservative in raw materials used in production. For example, a patient who reacted to a facial mask gel had a positive patch test reaction to MI, the facial mask gel, and sodium hyaluronate, the raw ingredient in the gel. Further analysis revealed that MI was unexpectedly present in the sodium hyaluronate.25 Similar scenarios have been reported in association with facial wet wipes,26 an exfoliating facial sponge,27 and a polyurethane sponge from a wound vacuum pump,28 among others.
