Allergy to nickel occurs, in sensitive individuals, mainly as a result of contact with objects containing it. More rarely, also due to inhalation or ingestion of some foods and waters.
Nickel allergy, ubiquitous risk
Nickel (Ni) is a natural component of the Earth’s crust. It is found in various minerals, in soils (including the ocean floor) and among the components of volcanic emissions.
Nickel’s high ductility encourages its use-in combination with other metals (e.g., iron, copper, chromium, zinc)-to create metal alloys characterized by hardness and resistance to corrosion and heat.
From coins to pots and pans
In addition to coins, nickel is found in costume jewelry products, metal buttons, batteries, cosmetics, lacquer, hair dye, toothpaste, shampoo, makeup, nail polish, etc.
It is also used in the making of pots and pans, especially those made of stainless steel. In fact, the initials 18/10 engraved on the pans mean that the stainless steel alloy was made with 18% chromium and 10% nickel.
Nickel in the environment
The presence of nickel in the environment is due to its release from industries that use it, as well as coal plants and incinerators. Dispersed in the air, it adheres to dust particles by depositing on the ground. Through industrial discharges then, Ni ends up in water and is deposited on bottoms and sediments.
Finally, nickel occurs naturally in some foods. Sometimes to an important degree, sufficient to trigger a reaction in allergic individuals.
The sources of exposure
Population exposure to nickel occurs mainly through the consumption of:
– Foods that contain it in nature. The highest levels are found in cocoa, nuts, hazelnuts and peanuts, legumes, and licorice. But also in many vegetables and fruits, such as asparagus, spinach, onions, mushrooms, kiwi, tomatoes, and broccoli. As well as in foods cooked or stored in metal containers. In contrast, nickel does not accumulate in fish tissue or in the meat of other animals,
– drinking water. Although to a lesser extent than in food, nickel can also remain in water. Due to release from water pipes or metal fittings, or natural release from rocks and soil into groundwater. In drinking water for human consumption and natural mineral water, nickel shall not exceed 20 micrograms per liter,
– Direct skin contact with nickel-containing objects and products,
– Inhalation of contaminated air, smoking (active and passive) tobacco.
Occupational exposures to nickel typically occur by inhalation, during industrial processes where the metal is used.
The health effects
When ingested, nickel is partly absorbed in the intestines (about 20-25%), in the large part excreted with feces. The portion that enters the bloodstream is then eliminated through urine.
Children show the same reactions as adults to the effects of nickel. Their chronic exposure through the diet, moreover, appears to be greater.
Researchers at the University of Giessen (Schmidt et al., 2010) found that nickel in humans directly activates Toll-like receptor 4 (TLR4), one of the cellular receptors that act as guardians of innate immunity, the body’s first line of defense against pathogens. By activating this receptor, the metal generates a ‘danger signal’ that promotes inflammation-causing itching, swelling and rashes-and recruits other immune cells.
The most serious health effects occur in the two cases of:
– Ingestion of high amounts of nickel or some of its compounds. With risk of poisoning and even severe gastrointestinal disorders,
– Prolonged low-dose exposure. Mammalian trials show adverse effects on the reproductive system. EFSA in 2020 indicated aTolerable Daily Intake (TDI) of 13 µg/kg body weight to protect the nonnickel-sensitized population.
Nickel in the professional field
Much more serious is exposure in professional settings. In this context, inhalation of high doses is related to skin and kidney reactions, chronic bronchitis, reduced lung function, and lung and sinus cancers.
For this reason, the International Agency for Research on Cancer (IARC) classifies some nickel compounds, taken only by inhalation, in Group 1 among human carcinogens, and nickel metal in Group 2B, that is, among substances that are potentially carcinogenic to humans.
In contrast, there is no evidence that nickel and its compounds are carcinogenic when ingested or in contact with the skin.
Allergic reactions
The most common health effect is the acute type of allergic reaction. Approximately 20% of the female population and 2-10% of the male population manifest hypersensitivity to nickel, acquired as a result of direct skin contact with objects or other products containing it and, only more rarely (about 20% of cases), by inhalation or ingestion through food or water.
In individuals sensitized to nickel, subsequent contact with the metal can produce a true allergic reaction. The first symptom occurs within 48 hours of contact with a contact dermatitis (redness, itching, and small blisters at the site of contact). Regardless of the form of exposure, so also by ingestion. In already sensitized individuals, a dose of 4.3 micrograms per kilogram of body weight of nickel can cause systemic contact dermatitis. To avoid these risks, exposure should be at least 30 times lower.
SNAS syndrome
Individuals who experience dermatitis at sites other than the point of contact, especially following nickel ingestion, suffer from ‘systemic nickel allergy syndrome,’ also known by the acronym SNAS.
The symptoms are different:
– Diffuse urticaria, eczema, itching or erythema,
– asthma attacks,
– Digestive disorders, abdominal pain, diarrhea or constipation, meteorism,
– Headache, asthenia.
Nickel allergy, the diagnosis
Nickel exposure can be detected by tests that measure the presence of the metal in blood, feces and urine. However, the positive result is not a sure indicator of disease, as nickel is present in commonly used products and foods.
If there are symptoms that can be associated with an allergy, the doctor will be able to recommend specific tests such as patch testing at specialized centers. Possible confirmation is followed by consultation with a specialist who, depending on the case, might prescribe medication (antihistamines), or desensitizing treatment with nickel sulfate, or an ad hoc diet.
For the diagnosis of occupational nickel diseases, the pathway is the same as that followed for chronic bronchitis, asthma, lung cancer, and sinus cancer.
Precautions
Avoiding exposure to nickel requires extreme caution because of the widespread presence of the metal in the environment and in various products. Some useful pointers:
– when choosing cosmetic items and products, select those labeled ‘tested for nickel’(nickel tested) or ‘nickelfree’ (nickel free). These claims ensure that the level of nickel is below allowable limits. Although the use of nickel is banned in cosmetics, it can remain there due to ‘impurities’ in the raw materials. Contamination of no more than 1 microgram of nickel per gram of cosmetic product (one part per million, ppm) is considered the no-effect threshold. And it is sometimes indicated on the label as ‘<1ppm’,
– Stop smoking, or at least do not exceed 3-4 cigarettes per day,
– Favor cooking food in pyrex, glass, aluminum, and unglazed ceramic cookware,
– Limit consumption of foods characterized by high nickel content as much as possible. Favoring fruits and vegetables that contain less, such as radicchio, endive, songino (valerian), fennel, eggplant, zucchini, peppers, cucumbers, beets, watermelon, cantaloupe, citrus fruits, peaches, bananas, strawberries, and grapes.
As seen above, there is more nickel in plant-based foods than in animal-based foods. Consequently, a vegetarian or vegan diet could increase exposure to the metal. However, it would be wrong to eliminate these foods from the diet, not least because nickel performs the useful function of aiding iron absorption.
Marta Strinati
Sources
ISShealth. Health from A to Z. Nickel. https://www.issalute.it/index.php/la-salute-dalla-a-alla-z-menu/n/nichel#diagnosi-e-terapia
Umberto Veronesi Foundation, magazine. Nickel allergy, what precautions to take in cooking? https://www.fondazioneveronesi.it/magazine/articoli/lesperto-risponde/allergia-al-nichel-quali-precauzioni-prendere-cucina
Katsnelson-style. Nickel allergy tracked to a single receptor. Nature doi:10.1038/news.2010.407
Bergman, Daniel & Goldenberg, Alina & Rundle, Chandler & Jacob, Sharon. (2016). Low Nickel Diet: A Patient-Centered Review. Journal of Clinical & Experimental Dermatology Research. 07. 10.4172/2155-9554.1000355
Sharma A. D. (2013). Low nickel diet in dermatology. Indian journal of dermatology, 58(3), 240. https://doi.org/10.4103/0019-5154.110846
Nickel allergy. Mayo Clinic https://www.mayoclinic.org/diseases-conditions/nickel-allergy/symptoms-causes/syc-20351529
EFSA, Update of the risk assessment of nickel in food and drinking water https://www.efsa.europa.eu/it/efsajournal/pub/6268
Professional journalist since January 1995, he has worked for newspapers (Il Messaggero, Paese Sera, La Stampa) and periodicals (NumeroUno, Il Salvagente). She is the author of journalistic surveys on food, she has published the book "Reading labels to know what we eat".
