The symptoms of metal hypersensitivity are caused when the body's immune system starts to view metal ions as foreign threats. The cells that make up the immune system normally kill foreign bacteria and viruses by causing inflammation. If they begin attacking metal ions that you touch, eat, inhale, or have implanted in you, they can produce a variety of symptoms (see the symptoms and complications section, below).
Potential metal allergens (triggers of allergic reactions) are very common in everyday life. Typical sources such as watches, coins, and jewellery come readily to mind. However, there are also other less obvious sources of metal in our daily lives. For example, cosmetic products and contact lens solutions may also contain metals that can trigger a reaction at the area of contact.
Nickel is one of the most frequent allergens, causing significant local contact dermatitis (skin reddening and itching). Cobalt, copper, and chromium are also common culprits. These metals can be found in consumer items such as jewellery, cell phones, and clothing items.
Aside from everyday items, medical devices also contain possible allergens such as chromium and titanium. Older dental implants and fillings are often made of metals. A few intra-uterine devices (IUDs) for birth control are made of copper and can also cause hypersensitivities. Implantable devices such as artificial knees, artificial hips, pacemakers, stents, and fracture plates, rods, or pins may contain metals that can cause metal hypersensitivity reactions. These reactions are often more severe in nature when the allergens have been implanted within the body for an extended period of time.
In addition, people who already have an autoimmune disorder (a disorder where the immune system is overactive) can have a higher risk of a metal hypersensitivity, as their immune system is in a constant state of activity.