Metal allergies occur when people are exposed to certain metals and become sensitized to them. Once this process has taken place, a person will suffer an allergic reaction on the next exposure to the metal.

Metals that frequently are the source of metal allergies include:

• Nickel. The main culprit in metal allergies, it is found in many forms of jewelry. Nickel is also found in numerous other metal items, including zippers, buttons and snaps. Sweat allows metal ions to be absorbed more easily into the skin, making the problem worse in body regions prone to perspiration.
  
  
• Cobalt. Another common allergen, it is found in many of the same products as nickel. It is also found as a natural element in soil, dust and seawater. Cement, bricks, mortars and metal alloys also contain cobalt. So do blue pigments in porcelain, glass, pottery and ceramics, and in blue and green watercolor paints and crayons. It may be present in manufacturing processes for polyester resins. As a result, anything containing polyester may include cobalt.
  
  
• Chromate. The best–known form of chromate is a shiny finish applied to metal products (chrome). However, this form of chromate is unlikely to trigger symptoms. Another form of chromate, chromium salts, is the more common allergen. Chromium salts are present in cement, concrete and similar construction materials. They are used as a leather tanning agent and can cause “shoe dermatitis” in people who wear leather shoes that contain chromate. Some matches also contain chromate and touching unlit or previously lit matches can cause reactions on fingers or on any part of the body those fingers touch.
  
  
• Amalgam allergies. A rare reaction to the mercury used in the most popular form of dental filling.  Patients who suffer amalgam allergies typically have a medical or family history of allergies to metals. In such cases, another restorative material must be used on the patient.

A huge array of everyday products may potentially trigger reactions in people with metal allergies. Below is just a sampling of products known to contain nickel, cobalt or chromate:

Nickel and other metals may be listed by other names, including:

Many implanted devices (e.g., surgical clamps, coronary stents) consist of, or contain, metals that can cause sensitivity or allergic reactions. As a result, patients should make all of their physicians aware of their metal allergies once they have been diagnosed.