The European baseline series and recommended additions: 2019

The European baseline series (EBS) of haptens (contact allergens) is used throughout Europe as an essential patch test screen to diagnose allergic contact dermatitis as an underlying contributory factor to, or cause of, eczema/dermatitis or other inflammatory dermatoses. Exposure to environmental haptens is continuously changing, and the EBS needs to be adapted to reflect these varying hazards that become a risk to the population following exposure,1 in order to ensure that the haptens tested remain relevant and new frequent haptens are detected. The EBS was last revised in 2015.2 Updates had been undertaken by the European Environmental Contact Dermatitis Research Group on behalf of the ESCD. Criteria for inclusion of haptens within the baseline series have been published.3 After a meeting at the biennial congress of the ESCD in 2016, it was decided to create an open and responsive process to update the EBS. The results of screening with the baseline series have been published by the European Surveillance System of Contact Allergy, which is a working group of the ESCD, and evidence-based changes have been recommended.4, 5 In 2017, a working party of the ESCD was formed that met twice during the year to propose changes largely based on these publications, which were subsequently put out for review to the membership of the ESCD. Following feedback, an update to the EBS was agreed, and is published here (Table 1). In brief, because of infrequent positive results4 and lack of relevance, it was agreed to delete primin 0.01% pet. and clioquinol 5% pet. It was further agreed to add propolis 10% pet. and 2-hydroxyethyl methacrylate (2-HEMA) 2% pet.5 Specifically, despite some cross-reactions, for example, to Myroxylon pereirae, it was the general opinion that propolis was a useful addition, especially where “natural” products were popular. Continuing reports emphasize the increasing relevance of contact allergy to 2-HEMA.6-8 When testing with acrylates is performed, it is important to load the chamber at the time of application, owing to the volatile nature of the hapten.9 Finally, the use of caine mix III 10% pet. instead of benzocaine 5% pet. was agreed, given the publications10, 11 showing the increased sensitivity of the mix in screening for contact sensitivity to local anaesthetics. It was felt that some of the haptens proposed5 did not meet the criteria for inclusion3 but that, while further information was gathered to confirm or refute their importance, centres should consider the potential value of testing with them in their local populations. These recommended additions to the baseline series are shown in Table 2. Active sensitization as a consequence of patch testing remains a significant concern. Although 2-HEMA 2% pet., according to the experience of the centres testing with it, did not result in active sensitization, this has been reported,19 and methyl methacrylate and other low molecular weight acrylates are weak sensitizers20 in the local lymph node assay. There is also a debate about p-phenylenediamine (PPD) 1% pet.21 In children, in whom no relevant exposure has occurred, it would be reasonable to exclude PPD, epoxy resin, and 2-HEMA. In adult males in whom no obvious exposure has occurred, and because of the low detection rate, there is an option to exclude 2-HEMA. It is the intention of the group to institute an iterative process with a biennial update of the EBS coinciding with the Congress of the ESCD to which all members of the ESCD will have the opportunity to contribute.