Sensitization to cobalt associated with nickel allergy: clinical and statistical studies

In 76 cases (5.8%) of a population of 1310 cases (examined by patch tests for possible contact dermatitis) a combined (coupled) allergy was found to nickel and cobalt. In 37 out of the 76 cases this combined allergy was associated with clinical dermatitis of the hands. Statistical chi-square analysis revealed that in the original population of patients examined, apart from a strong association between nickel and cobalt reactions, a significant association was also seen extending to the actual level (weakly to strongly positive) of reactions. Moreover this statistically significant association was still seen within the restricted population of combined nickel and cobalt allergics. Statistical association within the population of combined nickel and cobalt allergy between the strength of the Ni and Co reactions and positive reactions to other antigens of routine ICDRG-standard battery was not encountered, however. Positive reactions to cobalt were rare, but extreme. Nickel patients appeared to have about 50 times greater odds of being extreme cobalt positive. The possibility is discussed that facilitation of clinical cobalt allergy might be triggered by a high grade of nickel sensitivity.