Immunologic contact urticaria.

The wheal and flare reaction from direct contact with a chemical or protein agent is known as contact urticaria. Contact urticaria can be either nonimmunologic (no sensitization required) or immunologic (sensitization required). Immunologic contact urticaria often gives a more aggravated response and has the potential to spread from the local vicinity. Skin testing in immunologic contact urticaria gives a quicker response compared with skin testing in nonimmunologic contact urticaria. There are a wide variety of agents that can cause immunologic contact urticaria, and they can be either low-molecular-weight chemicals (haptens) or proteins.