[Nihil certum: historical development of the term prurigo].

The term prurigo is still used to designate primary dermatoses and secondary reaction patterns. A clear definition of the term is not available nor a clear clinical classification of diseases categorized under the term. Furthermore, there is no certainty about the entity it was primarily used to refer to, and whether it should always be considered in relation to pruritus. The concept appears already in very early medical treatises. From the very beginning, it was used in dermatology in a non-uniform way, and was alternately accorded and denied the status of an independent disease entity. Moreover, prurigo was subdivided into many different forms, but their descriptions are partly very similar, so that, for instance, it is quite difficult today to draw any conclusions about the clinical entities the frequently used terms prurigo mitis and prurigo formicans referred to. In contrast, the term prurigo nodularis is still commonly used. This article traces exemplarily the use of the term prurigo in the standard medical textbooks up to the definition of prurigo nodularis.