Contact urticaria is a wheal-and-flare (small swellings on the skin surrounded by areas of redness) response occurring rapidly on the application of certain substances to intact skin. It is probably more common than currently recognised. It can arise from different mechanisms:
- An immunological mechanism. Like allergic contact dermatitis, it depends on previous exposure to the substance and development of an immune reaction to it, ie sensitisation. The immune cells involved with contact urticaria are called immunoglobulin E or IgE cells. Once sensitised, subsequent exposure causes a reaction between the sensitiser, IgE cells and Mast cells, leading to the release of chemicals that cause an immediate wheal-and-flare response( this is a type I or immediate hypersensitivity response).
- A non-immunological response (direct histamine release). Not all cases are due to sensitisation. The chemicals causing the wheal-and-flare response can also be released by non-allergic mechanisms.
- A large sub-group have unknown causes.
Type I immunological reaction mechanism
Currently, the most important cause of occupational immunological contact urticaria is natural rubber latex. Substances capable of causing non-immunological contact urticaria that are seen occupationally include cobalt and platinum salts and balsams.
Persulphates can cause contact urticaria of uncertain cause in hairdressers and chemical workers.
Common work-related causes can be found in causative agents and occupations at risk.