Background: Previous research indicates that positive patch tests to nickel (II) sulphate, cobalt (II) chloride and potassium dichromate commonly occur together.
Methods: To further examine the relationship between nickel, cobalt, chromate, and the factors that may potentially be related to concurrent sensitizations to two or all three metal allergens, data from the Information Network of Dermatology Departments (IVDK, http://www.ivdk.org) have been investigated.
Results: Women had a higher conditional odds of concurrent nickel–cobalt (OR = 6.80; 95% CI: 5.65–8.19) and nickel–chromate (OR = 2.13; 95% CI: 1.67–2.72) reactions than men. Construction workers had a significantly higher odds of cobalt–chromate reactions (OR = 13.89; 95% CI: 10.36–18.64), while the odds of isolated cobalt allergy was only 0.92 (95% CI: 0.48–1.74). Patients with underlying atopic eczema/dermatitis syndrome had a 40–90% higher chance of any positive outcome, which involved chromate. Polysensitization, defined as the number of positive reactions to standard series substances other than nickel, cobalt, and chromate, was also significantly associated with the concurrent reactions; moreover, steady and significant effect gradients were noted.
Conclusions: This research confirms the occupational nature of cobalt–chromate concurrent reactions, in particular, in construction workers. Polysensitization, which is considered to represent susceptibility to delayed-hypersensitivity in general, is also associated with the concurrent reactions to the metals. Hence, not only coupled exposure, but also individual susceptibility may be responsible for concurrent reactions to metals in man.