Oral challenge with nickel and cobalt in patients with positive patch tests to nickel and/or cobalt.

During a 3-year period, 146 patients with positive patch tests to nickel and/or cobalt, for whom a systemic cause of dermatitis was suspected, were challenged orally with a single dose of 2.5 mg nickel given as nickel sulphate and 1 mg cobalt given as cobalt sulphate using a double-blind, placebo-controlled method. No following-up was possible for 2 patients. Seventy-five of the remaining 144 (52%) had flares of their dermatitis after challenge with nickel and/or cobalt, while 45 patients (31%) had no reaction and 24 (17%) reacted only to the placebo or to the placebo in combination with nickel or cobalt. Seven out of 13 patients with positive patch tests to cobalt experienced flares of their dermatitis only after challenge with cobalt.