This review concentrates on some specific aspects of the chemistry of allergic contact dermatitis. The way low molecular weight chemicals react with skin proteins to form complete antigens will be discussed and the development of molecular modelling techniques to analyse molecular recognition presented. Subsequently, how knowledge of the chemical structure can be used to estimate the allergenic activity of a molecule will be considered. This aspect includes work with qualitative and quantitative structure-activity relationships (SAR) in the field of contact allergy.