Nickel allergy is more common in women, probably because they are more likely to have pierced ears than men, although this is changing.
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Allergenic effects of metals and dental casting alloys
Allergy to nickel is a phenomenon which has assumed growing importance in recent years, largely because of the introduction of cheap fancy jewelry in which the underlying metal layer consists of nickel. 10 to 12% of the female population and 6% of the male population are estimated to be allergic to nickel. In fact the allergy is not caused by nickel itself but by the nickel salts which are formed under the effect of perspiration in contact with the piece of jewelry piece or watch. This phenomenon is always accompanied by corrosion of the object. (reference)
The degree of allergy varies. Some people develop dermatitis (also called eczema) from even brief contact with nickel-containing items, while others break out only after many years of skin contact with nickel. Some people develop intermittent or persistent eczema on their hands and feet. It is usually a blistering type of eczema, known as pompholyx. Sometimes it is due to contact with metal items containing nickel, but often there is no obvious reason for it. It has been suggested that in some, dyshidrotic hand dermatitis is due to nickel in the diet. Unfortunately it is not possible to avoid ingesting nickel as it is present in most foodstuffs. A low-nickel diet is only rarely helpful.
If you suffer from this type of allergy you should avoid contact with nickel-containing metals. Test your metal items to see if they contain nickel. Obtain a nickel-testing kit from your dermatologist or pharmacist. The kit consists of two small bottles of clear fluid. One contains dimethylglyoxime and the other ammonium hydroxide. When mixed together in the presence of nickel, a pink color results. Apply a drop from each bottle on to the metal item to be tested, first try it on a 10 cent coin. Use a cotton bud to rub gently - observe the color on the bud. If it remains clear, the item has no free nickel and will not cause dermatitis.
If it is pink it contains nickel and may cause problems if the metal touches your skin. The chemicals will not harm your jewelry.
Jewelry: Necklaces, necklace-clips, earrings, bracelets, watch-straps and rings may contain nickel. "Hypoallergenic", solid gold (12 carat or more) and silver jewelry should be safe. Nine carat gold and white gold both contain nickel. Plastic covers for earring studs can be obtained. Coating the stud with nail varnish is not recommended.
Clothing: Metal zips, bra hooks, suspender clips, hair-pins, buttons, studs, spectacle frames etc. are likely to contain nickel. Use substitutes made of plastic, coated or painted metal or some other material.
Personal articles: Consider lipstick holders, powder compacts, handbag catches, cigarette lighters, razors, keys, key rings, pocket knives, pens as potential causes of dermatitis.
Metal items in the home: Cupboard handles, kitchen utensils, cutlery, toaster, metal teapots, scissors, needles, pins, thimble, vacuum cleaners, torches, bath plugs... may all contain nickel. Choose tools with plastic handles. Stainless steel does not usually cause dermatitis unless it is nickel-plated.
Money: Silver coins are composed of cupro-nickel. Cashiers with nickel allergy may develop hand dermatitis from this source. Wear gloves to handle money or pay with a credit card or check.
Metal at work: Nickel dermatitis may be aggravated by contact with paper clips, typewriter keys, instruments, metal fragments from a lathe or chain saw.