nickel is the most frequent cause of contact allergy worldwide. Once sensitized, the allergic reaction persists indefinitely and can be triggered by both cutaneous and dietary exposure.
Epidemiology
- Prevalence: 8-19% of adults, 8-10% of children in Europe [ahlstrom 2019 nickel allergy review].
- Strong female predominance: 4-10x higher in women (14-20% women vs. 2-4% men in US) [tuchman 2015 nickel dermatitis children].
- Higher in dermatitis patients: 12-25% adults, 5-30% children.
- Prevalence declining in some European countries following EU Nickel Directive (1994), but new exposure sources (electronics) keep rates high.
Immunological Mechanism
A Type IV (delayed) hypersensitivity reaction [ahlstrom 2019 nickel allergy review, tuchman 2015 nickel dermatitis children]:
1. Nickel ions penetrate the stratum corneum (lag time ~50h, but rapid deposition in seconds-minutes of contact).
2. Dendritic cells take up and present nickel to T cells (Th1 and Th17).
3. TLR-4 activation is key — nickel directly activates the innate immune system via toll-like receptor 4, triggering inflammasome.
4. Sensitized T cells become clonal and traffic to skin areas.
5. Re-exposure triggers cytokine release → apoptosis of nickel-loaded keratinocytes via perforin-dependent mechanism.
6. Both CD4+ and CD8+ T cells involved; regulatory T cells (CD4+CD25+) found in non-allergic individuals provide tolerance.
Clinical Presentations
1. Localized contact dermatitis: at site of direct metal contact (earlobes, wrist, infraumbilical).
2. Ectopic: nickel transferred from hands to face/body.
3. Idiopathic ("id" reaction): auto-eczematization at flexural extremities, symmetric.
4. Systemic contact dermatitis: from dietary nickel ingestion — can cause widespread dermatitis, hand eczema, and "baboon syndrome" [tuchman 2015 nickel dermatitis children].
Nickel Allergic Contact Mucositis (Ni ACM)
- Nickel can also cause intestinal mucosal inflammation — a Type IV immune response in the gut [borghini 2020 low nickel diet celiac].
- Causes IBS-like symptoms: abdominal pain, bloating, nausea, loose stools.
- Also extraintestinal symptoms: dermatitis, headache, fatigue, joint pain.
- Prevalence may exceed 30% by epicutaneous patch test.
- Diagnosed via Ni oral mucosa patch test (omPT).
- Part of "systemic nickel allergy syndrome" (SNAS).
Dietary Nickel as Trigger
Dietary nickel can trigger systemic reactions in sensitized individuals [zirwas 2009 dietary nickel dermatitis]:
- Dose-response: 0.3mg oral NiSO₄ caused reactions in 40% of sensitized subjects; 4mg in 70%.
- A normal daily diet can easily contain >0.58mg nickel.
- Celiac disease patients on gluten-free diets may be at special risk because GF foods (corn, legumes, buckwheat) are high in nickel [borghini 2020 low nickel diet celiac].
Exposure Sources
Cutaneous: jewelry, belt buckles, coins, tools, dental materials, surgical implants, cell phones/tablets/laptops, stainless steel.
Dietary (see dietary nickel exposure): cocoa/chocolate, whole grains, legumes, nuts, seeds, canned foods, soy products, tap water, stainless steel cookware.
Regulation
- EU Nickel Directive (1994): limited nickel release from items in prolonged skin contact to <0.5 μg/cm²/week.
- Extended to piercings (2004) and further under REACH regulation.
- Led to measurable reduction in sensitization rates in European countries.
- No equivalent regulation in US, Asia, or most of the world.
Diagnosis and Treatment
- Patch testing: 5% nickel sulfate in petrolatum (gold standard).
- DMG spot test: dimethylglyoxime cotton swab test for screening items — turns pink if nickel release >0.5 μg/cm²/week.
- Low-nickel diet: effective for systemic symptoms. Avoid whole grains, legumes, nuts, chocolate, canned foods. Vitamin C and iron reduce absorption [zirwas 2009 dietary nickel dermatitis].
- Disulfiram: nickel chelator, useful adjunct but hepatotoxicity risk.
- Topical treatment: corticosteroids, calcineurin inhibitors.
Connections
- nickel — the causative metal
- dietary nickel exposure — oral trigger for systemic reactions
- oxidative stress — involved in tissue damage at contact sites
- Contrast with metal carcinogenesis — allergy is an immune-mediated, non-cancer endpoint