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Nickel allergyRadoslaw SpiewakInstitute of Dermatology, Krakow, PolandKey words: nickel, nickel sulfate, contact allergy, allergic contact dermatitis. Suggested citation format: Spiewak R. Nickel allergy. Allergopedia. 2025; 01: 02. DOI: to be announced Nickel is a component of numerous iron alloys (stainless steels) and is found in galvanic coatings on metal objects. Nickel can be found in earrings, rings, watches, buttons, zippers, coins, keys, scissors, batteries, musical instruments (metal strings, brass instruments), dyes, dentures and dental implants, orthopedic fixations and endoprostheses, razor blades and razors, eyeglass frames, kitchenware, tools, machine parts, and many other metal objects. The presence of free nickel ions on the surface of metal objects can be detected using the Chemo Nickel Test™ (Chemotechnique). Nickel can accumulate in used cooling and lubricating fluids and metalworking fluids. Clinical symptoms of nickel allergyIn most cases nickel causes skin inflammation (allergic contact dermatitis or eczema) limited to areas directly exposed to nickel by skin contact. Typical symptoms of nickel allergy include patches of itchy rash in the area of contact with metal objects releasing nickel, like fashion jewellery, metal buttons, rivets, zippers, buckless of garments, or areas exposed to contact with nickel-releasing tools, coins, keys, doorknobs, etc. Nickel can cause skin lesions resembling erythema multiforme and airborne eczema. Systemic reactivation of allergic contact dermatitis, i.e., dermatitis due to systemic exposure via ingestion or inhalation, e.g. from orthodontic appliances are possible, but infrequently reported. The possible role of nickel in food and drinking water is discussed below. Hematogenous eczema due to absorption of nickel at the primary contact site and redistribution to other skin areas via bloodstream is also possible, however, seems very rare. Sources of nickel sensitizationThe primary sources of nickel are metal objects that come in contact with the skin and release nickel. In the EU, consumer products intended for a prolonged contact with the skin, e.g., fashion jewellery, metal appliances in garments, are regulated by the "Cosmetic directive" (nowadays part of the REACH regulation). Please note that coins are not subject to the regulation and the Euro, as well as British Pound, Polish Zloty and many others do release substantial amounts of nickel. The same is true for coins circulated in the USA. Nickel in cosmeticsIn the European Union, the use of most nickel compounds in cosmetics has been banned due to their allergenic and carcinogenic potential. However, this ban does not apply to all nickel compounds, and the following nickel compounds are permitted for use in cosmetics:
INCI: International Nomenclature of Cosmetic Ingredients - unified, international names for cosmetic ingredients. Information about cosmetic ingredients is provided on the packaging in accordance with the INCI nomenclature. CI: Colour Index, a unique number of a dye in the Colour Index™ International (CI) reference database. Nickel in foodThe "low-nickel diet," also known as the "nickel diet," "nickel-free diet," or "nickel-free diet," is a very popular topic. Some doctors (including, unfortunately, dermatologists and allergists) uncritically recommend such diets to every patient with a positive nickel patch test. Online, you can find lists of foods that people with nickel allergies should supposedly avoid. I'll explain below why such lists should be treated with a great deal of skepticism. Meanwhile, scientific studies indicate that although the consumption of foods with high nickel content (e.g., canned food, seafood) may be a risk factor for the development of symptomatic nickel allergy [26], only 1-11% of all nickel-allergic patients experience skin problems caused by nickel in food [27,28]. It is worth realizing that oral doses of nickel capable of causing symptoms in allergic individuals are at least 1 mg and significantly exceed the typical daily exposure to nickel from food (0.22-0.35 mg Ni/day) [29]. In a study of Polish nickel-allergic patients, in some cases as much as 11 mg of nickel was necessary to induce symptoms [30] - a dose virtually impossible to achieve through the consumption of even the most "high-nickel" foods. An estimated 65 million Europeans are allergic to nickel [31], highlighting the scale of the problem and the social and economic consequences of uncritically recommending a "low-nickel diets" to every patient with a positive patch test result to nickel. Implementing a truly "nickel-free" diet is not only unjustified for most patients, but also simply impossible, as nickel is a common element in water and food. The most rigorous diets reduce the daily nickel intake by 50% at best, but even among patients who have successfully reduced serum and urinary nickel concentrations using a very restrictive diet, not all experienced improvement in their skin condition [32]. Therefore, implementing nickel-restricted diets should be reserved for carefully selected cases in which there is actual evidence that the patient will benefit from such a diet, and its effectiveness should be critically assessed after 4 weeks. In my practice, I have frequently encountered patients who, at the recommendation of their physicians, maintained a "nickel-free diet" for many years, at the cost of significant financial outlays and personal sacrifices, without achieving any noticeable benefits. Therefore, the decision to implement the diet should be based on the results of a placebo-controlled, double-blind trial (DBPCP). In the study by Veien et al. [33], approximately two-thirds of patients with a positive DBPCP result actually benefited from a low-nickel diet. In this group, patients who had strong nickel patch test reactions were less likely to experience improvement after a nickel-restricted diet. Due to the possibility of false-negative results, a positive nickel patch test result is not an absolute requirement for provocation, and patients with negative test results do respond to oral provocation [34]. However, such cases require particularly cautious interpretation. Performing a DBPCP in routine medical practice is quite cumbersome, therefore, if systemic nickel allergy is strongly suspected, a dietary nickel elimination and reexposure test is sometimes used instead of a DBPCP. Any assessment of the effectiveness of a low-nickel diet should be performed after at least one month of consistent use [33]. It is important to realize that determining which foods actually contain less nickel is very difficult, as the content of this element depends, among other things, on its concentration in the soil and water at the place of cultivation or breeding, and not only on the type of product, as suggested by the authors of various lists of foods "rich" and "low" in nickel [23]. In a Danish study, relatively high nickel content has been found in shrimp, mussels, beans, peas and green peas, kale, leek, lentils, lettuce, spinach, pea and alfalfa sprouts, cereal products, buckwheat, millet, oatmeal, bran, muesli, multigrain bread, figs, pineapples, raspberries and plums, chocolate, cocoa, marzipan, almonds, baking powder, linseed, hazelnuts, peanuts, soy products, sunflower seeds and licorice [29]. Furthermore, patients are advised to avoid dietary supplements containing nickel, as well as acidic foods cooked in steel vessels, canned food and hot drinks from vending machines and dispensers. Veien and Andersen [29] suggested maintaining a nickel-restricted diet for a month, after which a critical assessment of its effectiveness should be performed. Individuals who have not noticed improvement in their skin condition after a month of a low-nickel diet are not advised to continue it! Those who have experienced improvement are advised to slowly and gradually reintroduce the restricted foods to make the diet more tolerable, and in the event of a recurrence of symptoms, eliminate the offending foods. Due to the possibility of periodic spontaneous improvement in skin condition and the subjective nature of assessing disease severity, the effectiveness of such elimination diet can only be confirmed by complete resolution of the disease or significant improvement of eczema, persisting for at least 4 weeks after discontinuing pharmacotherapy, and a relapse after returning to the previous diet. If DBPCP is omitted, it is rarely possible to establish a cause-and-effect relationship solely based on elimination and reexposure, especially because cases of "positive reactions", i.e., worsening of skin condition has been also reported during DBPCP after consuming placebo, i.e., food containing no nickel. In light of the above-mentioned facts, in the absence of conclusive confirmation of dietary nickel hypersensitivity, it is safer to assume that the presence of this metal in food does not cause symptoms in a given patient. Such an assumption carries a significantly lower risk of error than the opposite assumption, moreover, it does not entail burdensome and costly interventions or restrictions and sacrifices that would reduce the patient's quality of life. Synonyms and names for nickel and its compounds in English and other languagesNickel; Nikkel; Nikiel; Nickel sulfate; Nickel chloride; Nickel gluconate; Nickel salt, N-acetylmethionine; Nickel bis(hydroxydiphenylmethylpyrrolidinomethyl)pyridinediyl T-butylisocyanoate perchlorate; Nickel; Nickel (II) Sulfate Hexahydrate; Nickel monosulfate hexahydrate; Nickel sulfate hexahydrate; Sulfuric acid, nickel (2+) salt hexahydrate; Single nickel salt; Nickel bis(hydroxydiphenylmethylpyrrolidinomethyl)pyridinediyl t-butylisocyano perchlorate; Nickel acetylmethionate; Nickel gluconate; Blue salt; Carbonyl nickel powder. Available diagnostic methods and materialsAt present, the only validated method of detecting nickel allergy is patch test performed in line with the current guidelines by national or intenational scientific societes, e.g., European Society of Contact Dermatitis. Patch test material available for testing includes:
Please note: Blood tests for nickel allergy (mostly advertised as "lymphocyte transformation tests"), although popular in some countries, have not been approved as a diagnostic tool, and their use in allergy diagnosis is controversial. Positivity rates19.7-24.5% of patients scheduled for routine patch testing. Cross-reactivities, co-positivities and co-sensitizationsPalladium is the most frequent and best-known cross-reactity of nickel. In the past, positive reactions to palladium were considered as cross reactivity secondary to nickel allergy, due to similar atomic structure and chemical properties of both metals. Nowadays, however, palladium is increasingly present in the everyday environment and isolated allergy to palladium (concomitant negative test to nickel) becomes more prevalent; there are also patients in whom allergy to palladium seems to be the primary event with clinical relevance, while nickel allergy seems to be the actual secondary cross-reactivity. DisclaimerThe above description does not exhaust all possible exposures and symptoms, and the hapten you are allergic to may also be present in other sources not listed above.Therefore, always check the composition of the products and substances you come into contact with, and if in doubt, consult a licensed physician, preferably a dermatologist or allergist.
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