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 are photosensitizing. Exposure to cobalt salts was responsible for the patients' chronic actinic dermati
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