Behaviour of contact allergy and new sensitivities on subsequent patch tests

Patch tests repeated one or more times over periods of up to 3 years in 208 subjects with allergic contact dermatitis produced evidence of persistent specific sensitivities in almost 50% of cases. In about 25% the reactivity disappeared and over 25% developed new sensitivities. No new sensitivities appeared in 253 patients with non-allergic contact dermatitis or with other types of dermatitis in whom the same patch tests were carried out. The history and follow-up of patients with new sensitivities brought into focus the presumed aetiopathogenetic role of further contacts, especially occupational or after topical applications. Patch tests themselves, provided the correct technique is employed especially as regards the concentration of allergens, do not seem to be responsible for new sensitizations to any significant extent.