Discussion
Cobalt is an ingredient of vitamin B12 or cobalamin, reaction to cobalt may cause problems in patients receiving vitamin B12 replacement therapy. Several cutaneous manifestations have been reported in patients with allergic contact dermatitis to cobalt undergoing oral cobalamin replacement including atopic dermatitis, chronic vesicular hand dermatitis, cheilitis, and stomatitis. (4)
Systemic contact dermatitis (SCD) is a condition occurring in previously sensitized individuals after systemic re-exposure to the same or cross-reacting substance. Sensitization occurs due to varying exposures to antigens via multiple routes through the circulatory system, and thereby produces systemic allergic dermatitis, which may result in a variety of skin eruptions and systemic flare. The exact mechanisms behind SCD are not fully understood, but is thought to be a T-cell mediated delayed type hypersensitivity reaction. (5) The common allergens inducing systemic contact dermatitis include nickel, zinc and cobalt. (6-8) Several systemic agents are associated with pigmentation including cytotoxic agents, antimalarial, analgesics and silver but pigmented systemic contact dermatitis after intake of cobalt containing diet has never been reported.
Osmundsen et al. first described pigmented contact dermatitis (PCD) as a non-eczematous variant of contact dermatitis, clinically characterized by hyperpigmentation with little or no signs of dermatitis by observations that the melanosis was due to contact dermatitis caused by an optical whitener containing pyrazoline present in a washing powder. (9) The exact mechanism which allergens induce hyperpigmentation remains unknown. Some experimental studies have shown that allergens having a special affinity for melanin induced cutaneous inflammation increasing the number and size of the melanocytes and enhancing their enzymatic activity (9, 10). The common allergens responsible for pigmented contact dermatitis are listed in Table 1. Related studies have demonstrated cases of pigmented contact dermatitis and histopathological examination revealed focal vacuolar degeneration of the epidermis and increased dermal melanophages with superficial perivascular lymphocytic infiltration. (11, 12) Although the exact mechanism of how cobalt induces systemic contact dermatitis remains unknown (13), one related study revealed the increasing prevalence of cobalt allergy in the general population and the high popularity of food supplements containing cobalt, e.g., vitamin B12 supplement. (14)