Dermal exposure to metallic nickel is possible wherever nickel powders are handled, such as powder metallurgy, and in the production of nickel-containing batteries, chemicals, and catalysts. Occasional contact with massive forms of metallic nickel could occur during nickel plating (anodes) and coin manufacturing (nickel alloys).
Skin sensitization to nickel metal can occur wherever there is sufficient leaching of nickel ions from articles containing nickel onto exposed skin (Hemingway and Molokhita, 1987; Emmet et al., 1988). However, cutaneous allergy (allergic contact dermatitis) to nickel occurs mainly as the result of non-occupational exposures. Indeed, in recent years, the evidence for occupationally-induced dermal nickel allergy is sparse (Mathur, 1984; Schubert et al., 1987; Fischer, 1989).
Sensitization and subsequent allergic reactions to nickel require direct and prolonged contact with nickel-containing solutions or nickel-releasing items that are non-resistant to sweat corrosion (see further discussion under Sections 5.2 and 5.4). The nickel ion must be released from a nickel-containing article in intimate contact with skin to elicit a response. Evidence suggests that humid environments are more likely to favor the release of the nickel ion from metallic nickel and nickel alloys, whereas dry, clean operations with moderate or even intense contact to nickel objects will seldom, alone, provoke dermatitis (Fischer, 1989). In some occupations for which nickel dermatitis has been reported in higher proportion than the general populace (e.g., cleaning, hairdressing and hospital wet work), the wet work is, in and of itself, irritating and decreases the barrier function of the skin. Often it is the combination of irritant dermatitis and compromised skin barrier that produces the allergic reaction (Fischer, 1989). The role of nickel in the manifestation of irritant dermatitis in metal manufacturing, cement and construction industries, and coin handling has been debated. It has been suggested by some researchers that nickel probably does not elicit dermatitis in workers from such industries unless the worker is already strongly allergic to nickel (Fischer, 1989). There are some reports that oral ingestion of high nickel levels (above 12 µg/kg/day) can trigger a dermatitis response in susceptible nickel-sensitized individuals (see section 5.3.3).