Predictive assays for evaluating the ability of materials to produce nonimmuno-logical contact urticaria have been developed. Lahti and Maibach (57) developed an assay in guinea pigs using materials known to produce urticaria in humans. One-tenth of a milliliter of the material (or control solvent) is applied to one ear of the animal. Ear thickness is measured before application and then every 15 min for 1 or 2 h after application. The maximum response is a 100% increase in ear thickness (within 50 min after application).
Materials can also be screened for nonimmunological contact urticaria in humans. A small amount of the test material is applied to a marked site on the forehead and the vehicle is applied to a parallel site. The areas are evaluated at about 20 to 39 min after application for erythema and/or edema (52).
Differentiation between nonspecific irritant reactions and contact urticaria may be difficult. Strong irritants (e.g., hydrochloric acid, lactic acid, and phenol), ^
can cause clear-cut immediate whealing if the concentration is high enough, but the reactions do not usually fade away quickly. Instead, they are followed by |
signs of irritation (erythema, scaling, or crusting) 24 h later. Some substances have only irritant properties (e.g., benzoic acid and nicotinic acid esters), some are pure irritants (e.g., SLS), and some have both these features [e.g., dimethyl «
sulfoxide (DMSO) and formaldehyde]. |
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Rosacea and Eczema are two skin conditions that are fairly commonly found throughout the world. Each of them is characterized by different features, and can be both discomfiting as well as result in undesirable appearance features. In a nutshell, theyre problems that many would want to deal with.