It is known from experimental studies that antigenic potency and the concentration of antigen determine whether exposure to an antigen will result in sensitization. A single accidental exposure to concentrated antigen may therefore induce primary sensitization. The purpose of this report was to collect clinical cases in which a single exposure had resulted in contact dermatitis suspected to be allergic. Only patients without previous relevant skin symptoms were included. Patch testing was used to demonstrate sensitization. 6 patients developed occupational allergic contact dermatitis from accidental exposure. Patch testing revealed allergy to diglycidylether of bisphenol A epoxy resin, polyfunctional aziridine hardener, methyl acrylate, phenol-formaldehyde resin, and methylchloroisothiazolinone/methylisothiazolinone (Kathon LX), respectively. Furthermore, 2 patients developed allergic contact dermatitis from their first exposure to tear gas chemicals, namely omega-chloroacetophenone and ortho-chlorobenzylidene malonitrile. A single exposure can therefore induce both sensitization and subsequent allergic contact dermatitis without further exposure. The allergens described must be considered strong allergens. The skin should immediately be cleaned if an accidental splash with such an allergen has taken place.