Frequency and trends of contact allergy to and iatrogenic contact dermatitis caused by topical drugs over a 25-year period.

BACKGROUND Allergic contact dermatitis is the most common adverse reaction caused by topical drugs. OBJECTIVES To study the demographic characteristics and lesion locations of patients with iatrogenic dermatitis, and to analyse contact allergy to active principles and trends in frequencies over the years. PATIENTS AND METHODS Between 1990 and 2014, 14 911 patients were patch tested with the European baseline series. Patients with a presumed iatrogenic cause were often tested with a pharmaceutical series, and, if indicated, with photo-patch tests. Most were also tested with the topical products to which they had been exposed, along with their ingredients. RESULTS Eight thousand three hundred and seventy-four (56%) patients tested positively, and 2600 (17.4%, 95%CI: 16.8-18.0%) of all patients suffered from iatrogenic contact dermatitis. The most important primary sites of dermatitis were the legs, face, and hands. The most common sensitizers included topical antibiotics, antiseptics, and corticosteroids. The most frequent baseline allergens in this subgroup were budesonide, neomycin, and benzocaine, although with a decreasing trend over the years. Many other allergens from different pharmacological classes were identified. CONCLUSIONS With a prevalence of 17.4% of consecutive patients, iatrogenic contact dermatitis is a frequent diagnosis in patients attending a general patch test clinic, involving one-third of the patients with at least one positive reaction.