Cutaneous nickel sensitivity in Toronto, Canada.

Patch tests were administered to 1074 subjects with suspected contact dermatitis by the method recommended by the International Contact Dermatitis Research Group. Of 629 subjects tested with 5% nickel sulfate in petrolatum, 10.5% had positive reactions (males, 5.1%; females, 16.7%). Of 447 subjects tested with 2.5% nickel sulfate in petrolatum, 11.9% reacted (males, 7.7%; females, 16.9%). In 447 subjects in whom the relationship between clinical findings and the patch test response was evaluated (i.e., relevance), more than 90% of the responses could be related to a past or present problem with contact dermatitis. The sites of involvement were not different between nickel-sensitive subjects and the overall population tested, except in the case of foot involvement, which was underrepresented in the nickel-sensitive group. Patients who had positive responses to nickel reacted more frequently to marginal irritants such as formaldehyde and benzoyl peroxide. This finding may suggest a reduction in the irritancy threshold in nickel-sensitive subjects. In most instances, domestic rather than occupational exposure was thought to account for the induction of nickel allergy.