Methylisothiazolinone, quo vadis ?

Methylisothiazolinone (MI) and the recent epidemic of contact allergy to it in Europe (and elsewhere) has been the subject of a number of editorials in this journal, which have also highlighted the inexcusable procrastination of regulators to address the problem and protect the consumer from this contact allergen. The present editorial aims at (i) giving an update on the current status of (lacking) regulations and (ii) pinpointing areas needing further attention, based on the current observations bundled in this issue of Contact Dermatitis. The Scientific Committee on Consumer Safety (SCCS; DG Sanco, European Commission) initially assessed MI as stand-alone preservative in cosmetic products (leave-on and rinse-off) in 2004 and considered it safe at 100 ppm (0.01%) use concentration, including the risk of sensitization, based on the dossier provided by industry for review at that time. In 2010 the first publication appeared which highlighted an emerging problem with MI in wet wipes causing allergic contact dermatitis (1). Many publications have followed showing an unprecedented increase in cases of allergic contact dermatitis to MI across Europe. In 2013 the EU Commission decided to reassess the safety of MI as a preservative in cosmetic products concerning sensitization. After several rounds of assessments and opinions the SCCS finally concluded in December 2015 that MI was ‘not safe as a preservative in leave-on cosmetics products’ and ‘a concentration of 15 ppm (0.0015%) MI is considered safe for rinse-off cosmetic products’ from the point of view of induction of contact allergy (SCCS/1557/15). This opinion was the same as published in 2013 (SCCS/1521/13) but there had been a series of objections by industry and requests to review again without additional substantive material being submitted. The member states adopted the ban of MI in leave-on cosmetics early in 2016 and the prohibition is expected to be in full force by the end of 2016. This means that leave-on cosmetics products containing MI must no longer be sold in the EU. Whether the maximum permitted concentration of MI in rinse-off products will be reduced is not decided yet; a decision by Member States is expected in spring 2017. Other types of products are regulated by classification and labelling (CLP). In March 2016 the Committee for Risk Assessment under the European Chemicals Agency (ECHA) proposed MI to be classified as “skin sensitiser 1A”; risk phrase H317 with a specific concentration limit≥0.0015%. This means that MI is classified as a potent sensitizer (group 1A) and products containing 0.0015% (15 ppm) or more MI shall carry a warning concerning the risk of sensitization either on the product or in the safety data sheet. This classification also implies that MI should be mentioned as an ingredient if present in 1.5 ppm or more. This classification is relevant for non-cosmetic products such as paints, glues and cutting oils etc. However, Member States have to formally adopt the proposal to bring this into force, which is expected in spring 2017, and it should then come into force in summer 2018. The above are important steps and, if finally adopted, are expected to improve protection for MI allergic individuals and prevent new cases. The first effect of the prohibition of MI in leave-on cosmetic products is already being seen. However, MI as a preservative has many uses, some unsuspected, which will continue to be a problem, which is illustrated by some of the contributions in this issue of Contact Dermatitis. First, undisclosed occurrence of this important contact allergen is a problem. Experienced clinicians may be exasperated over claims of "chemical innocence" of (cosmetic) products, including statements such as "100% natural". However, finding 400 ppm MI in a "completely natural" cosmetic sponge, thanks to the perseverance and diligent work-up usually necessary in such cases, Danish colleagues may have surprised even the hardened clinician (2). Not less surprising is the finding of MI in a designer spectacle frame (3), as biocides are usually only added to products or raw materials containing water, to prevent microbial degradation. The MI-allergic patient had suffered from long-standing contact dermatitis where the frames were in contact with the skin. After an accidental spill of methylchloroisothiazolinone (MCI)/MI, a worker developed not only a chemical burn, but also contact allergy to MCI/MI, which is well-described in the literature. However, during later treatment of his ulcerated burn with a vacuum pump applied with a polyurethane foam, an allergic reaction to this foam occurred. Only by chemical (HPLC) analysis Schliemann et al. were able to confirm the presence of both MCI (754 ppm) and MI (315 ppm) in the sponge material; the manufacturer had denied the presence of these substances or other biocides (4). In another case report from Denmark, MI was identified as the culprit