Contact urticaria.

Contact urticaria has been reported following skin contact with a multitude of substances ranging from simple chemicals to macromolecules. Its prevalence amongst the general population is unknown, but it may be a relatively common and under-recognized phenomenon. Non-immunological (irritant) causes typically elicit mild localized reactions, which clear within hours. Such agents can be found widely in food, cosmetics and medicaments. The lower diagnostic end-point for nonimmunological contact urticaria has been the subject of debate, which makes interpretation of the literature difficult. Immunological (allergic) contact urticaria is due to immediate-type hypersensitivity, and occurs most commonly in atopic individuals. It is mediated primarily by histamine, and may be associated with systemic, and potentially life-threatening symptoms. Natural rubber latex is one of the most important causes today, and the recent 'epidemic' of latex protein allergy has helped draw attention to this subject. Immunological contact urticaria to animal or vegetable matter may occasionally affect those who handle food, and other occupations such as agricultural and veterinary workers. This may be associated with development of a protein contact dermatitis. The diagnosis of immunological contact urticaria can often be confirmed by simple investigations such as skin prick testing or measurement of specific IgE.