Thermographic assessment of patch-test responses.

Infra-red thermography was used to quantify, at patch test sites, the allergic responses to experimental preparations of nickel sulphate and primary irritant responses to sodium lauryl sulphate in small groups of volunteers. The technique was also used to assess the patch-test responses in a much larger group of patients who had undergone routine patch testing for contact allergy with a wide range of test substances and among which there were large numbers of allergic, irritant and equivocal reactions. Thermographically, when compared to the surrounding normal skin surface, the sites of allergic reactions appeared as hot areas, the temperature and area of which were apparently dependent on the severity of the response. For allergic responses, there was a good correlation between the clinical assessment and either of two thermographic parameters, temperature and area of involvement. Compared with an aqueous solution of nickel sulphate, 'poor' formulations of the allergen, such as a suspension in soft paraffin base, elicited smaller and cooler reactions. Irritant reaction sites were not 'hot' and the temperature at such sites was no different from that of the surrounding normal skin. Infra-red thermography is a convenient non-invasive technique which apparently can be used to discriminate between irritant and allergic responses and to quantify the latter type of response.