The contact urticaria syndrome, or immediate contact reactions, comprises a heterogeneous group of inflammatory reactions that appear, usually within minutes, after contact with the eliciting substance. They include wheal and flare, along with transient erythema, and may lead to eczema. Nonimmunologic contact urticaria (NICU) occurs without previous sensitization and is the most common type of immediate contact reaction. This reaction remains localized; it does not spread to become generalized urticaria and it does not cause systemic symptoms. The strength of the reaction usually varies from erythema to an urticarial response, depending on the concentration, the exposed skin area, mode of exposure, and inciting substance (32,33). Animal models allow for identification of substances capable of immediate contact reactions. A substance can be applied to guinea pig ear lobe, with resulting erythema and edema if the substance indeed is capable of causing a contact urticarial response. Measuring changes in the ear lobe thickness with a micrometer caliper is an accurate, reproducible, and rapid method of quantifying edema. Ear lobe biopsies showing marked dermal edema and intra- and peri-vascular infiltrates of heterophilic (neutrophilic in humans) granulocytes are characteristics of NICU in the guinea pig ear (33,34).
The open test can be used to assess for NICU in humans. In this test, 0.1 mL of the test substance is spread on a 3x3 cm area of the skin on the upper back or extensor surface of the upper arm. The test site is observed for 60 minutes. Edema and erythema, or tiny intraepidermal spongiotic vesicles typical of acute eczema indicate a positive result. The test should first be done on nondiseased skin, and if negative, then on affected skin. The use test involves the patient handling the suspected agent as he/she handled it when symptoms occurred (33,35). Unfortunately, there are no vulvar experimental or epidemiological data on this topic.
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