Causes

The exact cause of nickel allergy is unknown. As with other allergies, nickel allergy develops when your immune system views nickel as a harmful, rather than harmless substance. Normally, your immune system only reacts to protect your body against bacteria, viruses or toxic substances.

Once your body has developed a reaction to a particular agent (allergen) — in this case, nickel — your immune system will always be sensitive to it. That means anytime you come into contact with nickel, your immune system will respond and produce an allergic response.

Your immune system's sensitivity to nickel may develop after your first exposure or after repeated or prolonged exposure.

Sources of nickel exposure

Common items that may expose you to nickel include:

• Jewelry for body piercings
• Other jewelry, including rings, bracelets, necklaces and jewelry clasps
• Watchbands
• Clothing fasteners, such as zippers, snaps and bra hooks
• Belt buckles
• Eyeglass frames
• Coins
• Metal tools
• Cellphones
• Keys
• Military "dog-tag" ID
• Chalk
• Medical devices
• Laptops or computer tablets
• E-cigarettes

Some extremely sensitive people may be affected by nickel-containing foods. Some foods that contain high amounts of nickel include soy products, peas, canned foods, cocoa powder, clams and cashews.