Efficiency in patch testing: the number needed to test to get one relevant result as a new approach in the evaluation of baseline series

Patch testing is a common procedure, where the baseline series is frequently used as a first screening. The number and the specific allergens of these series varies from country to country and keep changing over the years. Although the European Society of Contact Dermatitis (ESCD) made recommendations about patch testing1 , the decisions about the European baseline series were traditionally delegated to the European Environmental Contact Dermatitis Research Group (EECDRG)2 . A different, more reactive, approach has been recently proposed by the ESCD task force3 , using data provided by the European Surveillance System on Contact Allergies (ESSCA) to generate initial discussion. The main criteria for the addition of a new allergen is that the prevalence of allergy is 0.5-1% or higher4 , and positive results should be relevant.