Contact urticaria

Contact urticaria has been reported following skin contact with a multitude of substances ranging from simple chemicals to macromolecules. Its prevale nce amongst the general population is unknown, but it may be a relatively c ommon and underrecognized phenomenon. Non-immunological (irritant) causes t ypically elicit mild localized reactions, which clear within hours, Such ag ents can be found widely in food, cosmetics and medicaments. The lower diag nostic end-point for nonimmunological contact urticaria has been the subjec t of debate, which makes interpretation of the literature difficult. Immuno logical (allergic) contact urticaria is due to immediate-type hypersensitiv ity. and occurs most commonly in atopic individuals. It is mediated primari ly by histamine, and may be associated with systemic, and potentially life- threatening symptoms. Natural rubber latex is one of the most important cau ses today, and the recent 'epidemic' of latex protein allergy has helped dr aw attention to this subject, Immunological contact urticaria to animal or vegetable matter may occasionally affect those who handle food, and other o ccupations such as agricultural and veterinary workers. This may be associa ted with development of a protein contact dermatitis. The diagnosis of immu nological contact urticaria can often be confirmed by simple investigations such as skin prick testing or measurement of specific IgE.