The value of ongoing surveillance on the prevalence of contact sensitization.

Linked Article: Uter DOI: 10.1111/bjd.18946

In this issue of the BJD, Uter et al. describe the results of an ongoing surveillance study on the prevalence of contact sensitization in the population of Germany, Austria and Switzerland.1 It is, as the authors rightly comment, not based on patch testing samples of the general population, but ‘aimed testing’ in patients visiting the departments that are contributing to the database. Because reading a patch test result is prone to subjectivity and has a degree of interobserver and interdepartmental variability, it is reassuring to note that the participating centres meet regularly to harmonize their procedures, although it is not clear whether random external monitoring visits are being performed.2 It is still being debated whether patch test data from clinics, obtained by ‘aimed testing’, are indicative of what is happening in the general population. A few studies seem to confirm that, at least in a number of European countries, it is indicative.3 It is important to realize that the large dataset presented by Uter et al. is limited to the European baseline series. This series is supposed to be fairly representative, but a word of caution is needed because the hair dye ingredient para‐phenylenediamine is no longer routinely patch tested in Germany.

Large datasets allow researchers to show time trends. Indeed, Uter et al. show time trends in positive reactions to the preservatives methylisothiazolinone (MI) and methylchloroisothiazolinone (MCI)/MI, which is a long‐term indicator for MI allergy. The high prevalence of MI contact allergy, which had its peak around 2013–2014 in Europe, was a major trigger to ban of the use of MI in leave‐on cosmetic products and restrict the maximum permissible level to 15 p.p.m. in rinse‐off cosmetics.4, 5 The current publication by Uter et al. shows the rise and fall of contact allergy to MI, which demonstrates the success of the preventive measures that were implemented.

The data presented by Uter et al. on sensitization to the fragrances support the value of ongoing surveillance, because fragrance‐induced contact allergy is still considered to be of high concern. Industry is more and more relying on nonanimal, in vitro tests to assess the potency of sensitizers that are present in marketed consumer products, to be used in a quantitative risk assessment (QRA).6 This is promising but also shows the importance of collecting and monitoring well‐performed patch test data as a kind of feedback loop to the more ‘predictive’ QRA. Such a well‐monitored feedback loop is currently being implemented by the Extended Fragrance Ingredients Surveillance Study, to monitor the frequency of contact allergy to a defined group of existing ingredients and also to new fragrance ingredients, initiated by the International Dialogue for the Evaluation of Allergens project (IDEA; https://www.ideaproject.info).

Together, large datasets such as that presented by Uter et al. allow researchers to spot discrepancies and important time trends, which trigger us to regulate exposure to substances, for example by cosmetics regulation.