What causes allergies to nickel?
In order for an allergic reaction to occur, the skin of a sensitive individual must be in direct contact with the object containing the nickel. For watches, this necessarily means the case or the bracelet. Another condition for an allergic response is that the nickel must be liberated rather easily from its alloy onto the skin in the form of cations, or positively charged particles. Thirdly, these positive ions must be transported by some sort of fluid serving as an electrolyte. This liquid most often is sweat, but may also be water from the sea or from a swimming pool. The stainless steel used in the manufacture of watch cases liberates varying amounts of nickel ions depending on the nature of the alloy and the proportions of the individual components. A stainless steel created for medical purposes gives off practically no nickel.
Another important factor in the liberation of nickel ions is the condition of the metal surface that is in contact with the skin. Rough or porous surfaces retain the electrolytic fluid, usually perspiration, and thus become very active zones for producing the allergenic cations. The resulting corrosion of the metal then generates even higher concentrations of the metal ions. Upon examination of the back of a chrome-plated watch case that has been attacked by sweat, it is surprising to see how much corrosion has taken place and, therefore, easy to understand why the wearer’s skin can become sensitive (Figure 4).
In the meantime…
While waiting for such directives, there are several precautions that can be followed to prevent or diminish the risk of nickel allergies from watches. First, remove the watch at night to decrease the length of time it is in direct contact with the skin. Secondly, wipe the case often with a clean, dry cloth. A slightly damp cloth can be used if the watch is water-resistant. In addition to preventing the build-up of irritating nickel ions, this is a basic common sense measure of good hygiene.
Watchmakers have often expressed how surprised they are at the nonchalant attitude of many watch owners when it comes to the cleanliness of an object in direct and continuous contact with their skin. Thirdly, after perspiring heavily, the watch should be removed and washed. By caring for one’s watch in this way, the risk of allergies to nickel can be greatly reduced.