Before the arrival of modern pharmacotherapy, drug hypersensitivity reactions were virtually unknown. Toxicity from the many plant-, animal- and inorganic material-derived remedies must have been much more common. One famous example is the intoxications from mercury, which has been used in many ailments, but particularly for the treatment of syphilis. It was only in the 19th century when more and more active principles from e.g. plants were identified, and when the observations of skin reactions became more prevalent. In 1877, Heinrich Köbner used for the first time the term 'drug exanthema' (Arznei-Exanthem). Since then, many different types of exanthemas from the mild macular-papular forms to the severe life-threatening bullous exanthemas such as toxic epidermal necrolysis have been observed from numerous drugs. The systematic investigation of severe drug reactions has only started in the second half of the 20th century, parallel to the increasing knowledge in immunology. Drug hypersensitivity reactions still remain one of the most challenging problems in allergology due to their manifold clinical manifestations and their very diverse pathophysiology. The introduction of new drugs and in turn the emergence of new hypersensitivity reactions will remain a challenge in the future.