Photocontact dermatitis to cobalt salts

4 patients with chronic photocontact dermatitis were sensitive to cobalt salts. They presented as cases of contact dermatitis from cement or pig fodder with persistent lesions on exposed areas. Only 2 of them had standard patch test positive reactions to chromate and cobalt, but all showed positive photo-patch tests to cobalt. Photo-oxidation tests proved that cobalt salts are photosensitizing. Exposure to cobalt salts was responsible for the patients' chronic actinic dermatitis.