Nickel is a metal that is found in water, soil, air and the biosphere. It is used with other metals to form alloys and is widely used in the production of stainless steel. Nickel is one of the main elements responsible for allergic contact dermatitis.
According to data published by the European Surveillance System on Contact Allergies (ESSCA) in 2004, it was confirmed that the prevalence of the positivity of patch tests in the general population in Europe is around 20%; notably, Italy had the highest prevalence of people with nickel allergies in Europe at 32.1% while Denmark had the lowest prevalence with 9.7%.
A nickel allergy is manifested through different modalities: cutaneous, localised or systemic, and extracutaneous. We can distinguish:
The classic clinical form caused by a nickel allergy is allergic contact dermatitis (ACD). Nickel is responsible for 35% of ACDs related or not to professional activity. Dermatitis caused by contact with nickel is usually easy to recognize; it occurs in the form of zonal eczema confined to skin sites in direct contact with nickel-releasing objects, such as the earlobes (earrings), wrists (watches), neck (necklaces), or umbilical region (jeans buttons).
There is also another form, systemic nickel allergy syndrome (SNAS): In the 1970s, researchers found that a considerable number of patients with nickel-allergy that had been in contact with objects plated with this metal had dermatitis at sites other than these. The most common sites of these eruptions were the folds of the elbows, the neck and inner thighs, the palms of the hands, the lateral edges of the fingers, and the soles of the feet; Eyelid eczema and keratotic elbow eczema have also been frequently described. Due to the symmetry of the lesions, systemic absorption of nickel has been suspected, which can occur through the diet, for example. Manifestations can also include headaches, canker sores and gastrointestinal symptoms, which can easily overlap and be confused with those of irritable bowel syndrome.
The diagnosis of ACD (allergic contact dermatitis) is based on the Patch Test (a skin test) for Nickel, which consists of applying to the skin (usually on the back) a preparation containing Nickel for a period of 48 hours; after an additional wait time of 24-48 hours, an evaluation is carried out that confirms the reaction by the appearance, in the area of application, of a more or less pronounced erythemato-vesicular zone depending on the sensitivity of the subject.
On the other hand, to study the systemic nickel allergy syndrome, it is necessary (after checking the sensitisation by the Patch Test) to perform an elimination diet for a period of 2 to 3 weeks and to evaluate the clinical response, which must demonstrate a significant improvement.
Diagnostic information involves certain challenges, as information on the nickel content of foods is extremely heterogeneous. The concentration of nickel in soil, air and water is, in fact, extremely variable and difficult to determine. This is why the consensus on the presence of nickel is unanimous almost only for legumes (especially peanuts, beans, peas), shellfish, nuts and canned foods. It is important to point out, however, that many plant-based foods are responsible for the symptoms described.