The news about an upsurge in cases of allergies due to Methylisothiazolinone created a huge buzz in French media in December. This substance was often presented as a new preservative used in replacement of parabens, which is not really the case.
Already known adverse effects
Indeed, this preservative - which is authorized at a maximum concentration of 0.01% in cosmetic products placed on the European market - was not a newcomer and its potential adverse effects have been well documented for many years. The combination of Chloromethylisothiazolinone and Methylisothiazolinone, in proportion 3/1, is well known in the cosmetic industry under the trade name Kathon-CG. Once widely and commonly used, Kathon-CG was gradually abandoned and its use restricted to certain rinsed off products such as shampoos. Kathon-CG has been gradually replaced by parabens, which had the advantage of being much more tolerated. As a consequence, parabens were present in nearly 70% of cosmetic products, until they were questioned recently.
However, the use of Methylisothiazolinone rose again in recent years. Actually, the renewed interest in this substance, often described as less allergenic than Chloromethylisothiazolinone, is directly linked to the disgrace of parabens. Now, Methylisothiazolinone is one of the most frequently used preservatives in various paraben free toiletries (cleaning wipes, soaps, shampoos), but also in several household and industrial products.
According to Professor Annick Barbaud, Head of the Dermatology and Allergology Unit at Nancy’s University Hospital, the information provided by the French vigilance network on dermatologic allergies (Revidal) shows an upsurge in contact dermatitis linked to Methylisothiazolinone. Dr. Barbaud was taking stock of contact dermatitis on the occasion of Paris Dermatological Days, which were attended by over 6,000 people under the aegis of the French Society of Dermatology (SFD) from 10 to 14 December 2012, also reported "some rare cases of breathing difficulties and irritation of mucous membranes.” Furthermore, a recent Danish research even shows that non-contact exposure is a growing problem. 
Do safe alternatives exist?
This upsurge in allergies is not a surprise for experts. Indeed, the frequency of allergies related to preservatives is growing exponentially together with the population exposure, i.e. with the frequency of their use by the industry. It is therefore quite logical that the restored popularity of Methylisothiazolinone be followed by an increase in allergies related to this substance.
Does that mean that replacing parabens by safe alternatives is impossible? The French drug regulatory agency (National Agency for the Safety of Medicines and Health Products - ANSM) in an information notice, published in May 2011, said it was currently unlikely that “chemical alternatives offering a better safety profile and preservation efficacy equalling those of parabens could be offered. By definition, all preservatives are biologically active. Accordingly, any preservative can potentially lead to safety problems.”
In order to reduce the exposure to preservatives, including parabens, a decrease in the concentration of preservatives is not always possible because the anti-bacterial protection might become insufficient. In both in the pharmaceutical and cosmetic sectors, manufacturers are now encouraged to focus on physical methods, including through new packaging solutions. The development of single-dose and so-called airless packaging directly addresses this need.