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. 2025 Jul 3;93(4):275–284. doi: 10.1111/cod.14837

Nickel Allergy and Piercings: A Systematic Review and Meta‐Analysis

Benedikte von Spreckelsen 1, Mikkel Bak Jensen 1,2,✉, Jeanne Duus Johansen 1,2, Malin Glindvad Ahlström 1,3
PMCID: PMC12415668  PMID: 40611585

ABSTRACT

Nickel is the most frequent cause of allergic contact dermatitis in Europe and worldwide despite 20 years of regulation. The aim of this study is to systematically assess (i) the risk of nickel allergy associated with piercings and (ii) the proportion of earrings for piercings on the market that release excessive amounts of nickel. The databases PubMed, Embase, and Web of Science were searched. Regarding (i): nickel allergy was significantly associated with piercings in the general population (OR 5.9 [95% CI: 3.6–9.4], n = 5333) and in dermatitis patients (OR: 3.6 [95% CI: 2.3–5.8], n = 20 330). The etiological fraction was 82% (95% CI: 55.2%–92.8%) and 69.7% (95% CI: 62.7%–75.3%), respectively. Regarding (ii): critical nickel release, as determined by dimethylglyoxime (DMG) screening, was identified in 11.3% of European earrings, while a much higher proportion was found in earrings from Asia (34.5%) and North America (31.1%). Of concern, as determined by EN1811, 24.7% of European earrings intended for piercing exceeded regulatory limits. In conclusion, piercing poses a significant risk factor for nickel allergy and a large proportion of earrings still release nickel in amounts that may result in nickel allergy and allergic nickel dermatitis. Stricter enforcement of existing regulations and consideration of new measures are essential.

Keywords: contact allergy, DMG, earring, EN1811, jewellery, nickel, piercing

Nickel release from earrings for piercings: We reveal that a significant proportion of earrings on the market still release nickel in excess of regulatory limits. This finding underscores the need for stricter enforcement of existing regulations or consideration of new measures to mitigate nickel‐induced allergic contact dermatitis.

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1. Introduction

Nickel allergy is the most frequent type of contact allergy (CA) worldwide, including Europe, despite having been regulated in the European Union (EU) for two decades [1]. A recent meta‐analysis found that the prevalence of nickel allergy in the general population in Europe, North America, and China was 11.4% [2]. The prevalence among women was 4–10 times higher than among men, and the trend was the same in girls compared to boys, presumably due to differences in exposure patterns [3].

The EU nickel restriction came into force in 2000 and was adjusted in 2004 [4], when the nickel release limit from piercing post assemblies, i.e., studs inserted into pierced parts of the body, was restricted to less than 0.2 μg nickel/cm2/week [4]. The limit of nickel release from the decorative front part and the lock part of the earring, i.e., items that are in direct and prolonged contact with the skin, is restricted to a maximum of 0.5 μg nickel/cm2/week [5]. Coated products must comply with the EU nickel restriction for a period of 2 years of normal use [6, 7]. Piercing is defined as ‘the making of holes in parts of the body in order to wear a ring, etc. as a decoration’ [8]. The piercing procedure performed by a needle, or a piercing gun forms an artificial skin canal by penetrating the stratum corneum. Until epithelization is complete, the piercing stud remains in direct contact with the immune cells in dermis [1]. To our knowledge, exactly how the skin appears after epithelization when pierced has not been researched yet but may be crucial for understanding the risk of nickel allergy. Piercing is a well‐recognised risk factor of nickel allergy, although the risk has not been systematically reviewed or quantified. In this study, we perform a systematic review and meta‐analysis with the purpose to provide:

  1. An estimate of the risk of nickel allergy associated with piercings in the general population as well as in dermatitis patients stratified by age (children/adults) and sex (male/female).

  2. An estimate of the proportion of earrings for piercings on the market with excessive nickel release.

The hypotheses of the study were:

  1. Individuals with body piercings have a significantly higher prevalence of nickel allergy than individuals without piercings.

  2. A significant proportion of earrings marketed for use in piercings release nickel in amounts that exceed the EU safety limit (0.2 μg/cm2/week).

2. Methods

A study protocol was developed prior to the commencement of the research and registered in PROSPERO (CRD42024600336). The study follows the Preferred Reporting Items for Systematic Review and Meta‐Analyses (PRISMA) guidelines [9].

2.1. Literature Search

The literature databases PubMed, Embase, and Web of Science were searched on 23 October 2024. For studies reporting on nickel allergy and piercings, the following search terms were used: ‘(contact dermatitis OR allerg*) AND (jewelry OR jewellery OR body piercing OR pierc* OR earring) AND (nickel)’. Studies reporting on nickel release from earrings were searched using the following search terms: ‘(jewelry OR jewellery OR earring OR body piercing OR pierc*) AND (nickel)’. The specific search strings for each database are listed in Table S1. The reference lists of included articles were screened, and additional relevant studies were included.

All original studies in full text and in English, published no later than 22 October 2024, that evaluated (i) the prevalence of nickel allergy and piercings, and (ii) the prevalence of nickel release from earrings for ear piercings were included. No limit was set on study size. For (i), no retrospective time limit was applied. For (ii), only market surveys covering a study period after 2004 were included. Studies with overlapping data were excluded.

2.2. Data Extraction and Quality Assessment

Two authors (BvS and MBJ) independently screened and reviewed titles and abstracts in Rayyan [10]. Duplicates were removed. Possible discrepancies were settled through discussion among the two screeners. When all relevant studies had been included, one author (BvS) was responsible for data extraction. Data relevant for assessment was discussed with MGA and JDJ. For (i), an odds ratio (OR) table was filled in.

The Newcastle‐Ottawa Scale (NOS) was used to assess the quality of included non‐randomised studies [11]. An adapted version was used for cross‐sectional studies. Each study was awarded up to nine points. Studies with an NOS value of six or higher were considered high quality. All studies were included irrespective of their NOS scores (Table S2).

2.3. Data Analysis

Statistics analyses based on the extracted data were performed in the StatsDirect program version 3.1.4 (StatsDirect Ltd., Wirral, UK). The OR with a zero value in one of the fields of the OR table was calculated using continuity correction (0.5) [12, 13, 14]. Pooled ORs and pooled proportions were derived using random‐effects models, and 95% confidence intervals were reported. The heterogeneity of the included studies was assessed using the Cochrane Q and I 2 statistics. Due to the anticipated high heterogeneity of the included studies, pooled ORs and pooled proportion analyses were conducted using random‐effects models with the DerSimonian–Laird method. Forest plots for the meta‐analyses were constructed, and the risk of publication bias was examined through Egger's test and funnel plots. A study on female metalworkers was excluded from the meta‐analysis due to potential work‐related co‐exposure to nickel [15]. A study including earrings labelled as ‘nickel‐free’ exclusively was excluded from the meta‐analysis [16]. R version 4.3.2 was utilised to assess the etiologic fraction (EF) of nickel allergy cases attributed to piercings.

3. Results

The search strategy is shown in Figure 1. Regarding (i), a total of 483 nonduplicate studies were identified. After screening titles and abstracts, 54 studies were included for full‐text evaluation. One study could not be retrieved, and 27 studies were excluded due to the predetermined criteria. Screening the reference lists of the included studies did not yield additional studies. In total, 26 studies were included. In general, the risk of bias was low/acceptable according to the NOS score (Table S1).

FIGURE 1.

FIGURE 1

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(a) Prisma flow chart for (i). (b) Prisma flow chart for (ii).

Regarding (ii), 804 nonduplicate studies were screened for titles and abstracts. Thirty six studies were included for full‐text screening, of which 16 met the inclusion criteria. During additional screening, 43 studies were identified, but only one study was included. In total, 17 studies were included in the analysis. The heterogeneity of the studies included for (i) and (ii) was high (Tables S3 and S4).

3.1. Risk of Nickel Allergy With Piercings

3.1.1. General Population

The main study results for the general population can be found in Table S5. For studies of adults, the publication dates range from 1979 to 2022, with geographical coverage spanning Europe and North America. For studies involving children/adolescents, the study period was between 1982 and 2016 and included studies from Europe and South America. Some studies may have contributed multiple ORs due to factors such as differences in sex and the timing of ear piercings [14, 17, 18, 19, 20, 21, 22]. In one study, the ‘sex’ category ‘all’ was calculated by combining data from male and female participants [21].

The results of the meta‐analysis for the general population are shown in Table 1. Overall, 19 studies (11 764 individuals) reported on nickel allergy and piercings in the adult general population, and 13 studies (14 109 individuals) reported on children/adolescents. Based on five adult studies including both genders [12, 19, 20, 23, 24], the pooled OR was 5.9 (95% CI: 3.6–9.4, p = < 0.0001). The risk of getting nickel allergy when pierced was 4.6 (95% CI: 3.3–6.4, p = < 0.0001) for women (Figure 2) [17, 18, 19, 20, 25, 26, 27] and 2.8 (95% CI: 1.4–5.8, p = 0.0049) for men [19, 20, 28, 29]. In five studies of children of both sexes [21, 22, 30, 31, 32], the pooled OR was 4.7 (95% CI: 2.3–9.7, p = 0.0001), while the pooled OR for girls was 3.8 (95% CI: 2.6–5.7, p = 0.0001) [14, 21, 22, 33, 34], and the pooled OR for boys was 1.5 (95% CI: 0.8–2.9, p = 0.2523) [21, 22]. The pooled analysis of the etiological fraction from studies in the adult general population was estimated at 82% (95% CI: 55.2%–92.8%).

TABLE 1.

Odds ratio meta‐analysis of having nickel allergy and piercings for adults and children/adolescents in (a) the general population and (b) dermatitis patients.

(a) Random‐effects model (b) Random‐effects model
Group Studies (n) Pooled odds ratio (%) 95% CI p for χ 2‐test Type of test Studies (n) Pooled odds ratio (%) 95% CI p for χ 2‐test
Adults (all) 5 5.9 3.6–9.4 < 0.0001 Adults (all) 5 3.6 2.3–5.8 0.0001
Men 4 2.8 1.4–5.8 0.0049 Men 3 4.0 1.7–9.2 0.0014
Women 10 4.6 3.3–6.4 < 0.0001 Women 3 3.5 1.3–9.4 0.0104
Children (all) 5 4.7 2.3–9.7 0.0001 Children (all) 1 1.8 1.3–2.4
Boys 2 1.5 0.8–2.9 0.2523 Boys 1 1.4 3.4–5.1
Girls 6 3.8 2.6–5.7 0.0001 Girls 1 1.1 0.7–1.7
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Note: ‘All’ refers to the inclusion of both female and male participants in the study.

Abbreviation: CI, confidence interval.

FIGURE 2.

FIGURE 2

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Forest plot. Pooled odds ratio meta‐analysis with randoms effects of the risk of nickel allergy and piercings for women in the general population. Red coloured squares: studies with female participants.

3.1.2. Dermatitis Patients

The studies included in calculating the OR for the association between nickel allergy and piercings in dermatitis patients are presented in Table S6. For adults, the publication dates ranged from 1989 to 2017 and included studies from Europe, North America, and Asia. In two studies, ‘all’ was based on combined data from the ‘male’ and ‘female’ categories [13, 35]. Some studies contributed multiple ORs and so appear multiple times in the same meta‐analysis, reflecting variations in age or sex [13, 35, 36].

Overall, five studies (21 868 patients) reported on nickel allergy and piercings among adult dermatitis patients, and one study (918 patients) reported on children/adolescents. Based on five studies with both male and female patients, the pooled OR was 3.6 (95% CI: 2.3–5.8, p = 0.0001) [13, 35, 36, 37, 38]. For women, the pooled OR was 3.5 (95% CI: 1.3–9.4, p = 0.0104) [13, 35, 36]. For men, the pooled OR was 4.0 (95% CI: 1.7–9.2, p = 0.0014) [13, 35]. Only one study, from the United States, investigated the association between nickel allergy and piercings in children and adolescents [35], reporting an OR of 1.8 for both sexes (95% CI: 1.3–2.4), an OR of 1.1 for girls (95% CI: 0.7–1.7), and an OR of 1.4 for boys (95% CI: 3.4–5.1) (Table 1). The pooled analysis of the aetiological fraction in studies with adult dermatitis patients was estimated at 69.7% (95% CI: 62.7%–75.3%).

3.2. Excessive Nickel Release From Earrings Intended for Piercings

The earrings analysed in the included studies were purchased from a variety of sources, including marketplaces, chain clothing/department stores, large supermarkets, single fashion jewellery shops, accessories stores, local artists, freestanding booths in underground stations or malls, and a piercing studio [39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51]. Two of the included studies examined earrings from patients with allergic nickel dermatitis [52] and schoolgirls [53]. Some studies were included multiple times because they tested earrings in different countries, used different test methods, or analysed different earring parts. However, each earring or earring area was only analysed once in the meta‐analysis.

3.2.1. DMG Test

In the 13 included studies, a total of 2508 earrings were tested across Europe, Asia, and North America (Table S7). The study period was between 2007 and 2020. The proportion of earrings that were DMG‐positive was 11.3% in Europe (95% CI: 7.9–15.2) [42, 43, 44, 45, 46, 52, 53], 34.5% in Asia (95% CI: 29.0–41.3) [48, 49, 54], and 31.1% in North America [50] (Table 2, Figure 3).

TABLE 2.

Proportion meta‐analysis of positive test of earrings with nickel release according to geographical region.

Type of test Europe Non‐Europe
Asia North America
Studies (n) Proportion (95% CI) (%) Studies (n) Proportion (95% CI) (%) Studies (n) Proportion (95% CI) (%)
DMG 8 11.3 (7.9–15.2) 4 34.5 (29.0–41.3) 1 31.1
EN 1811 > 0.2 a 3 24.7 (19.2–30.7) 1 31.8 NA NA
EN 1811 > 0.5 a 4 10.2 (5.7–15.8) NA NA 1 33.3
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Note: Some studies are included two times according to earrings tested in different countries in the same study, the study using different test methods, or different parts of the earring are tested in the same study.

Abbreviations: CI, confidence interval; NA, not available.

a

Nickel release > 0.2 and 0.5 μg Ni/cm2/week.

FIGURE 3.

FIGURE 3

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Forest plot. Pooled proportion meta‐analysis with random effects of DMG‐tested earrings after year 2004. Red coloured squares: European studies, blue coloured squares: Asian studies, green square: North American study.

3.2.2. EN1811 Test

In total, 793 earring parts intended for direct and prolonged contact were tested (Table S8). The study period ranged from 2007 to 2014. Earrings that released > 0.5 μg Ni/cm2/week were reported in four studies from Europe [39, 40] and one study from North America [47]. The pooled proportion of earrings with nickel release exceeding 0.5 μg Ni/cm2/week was 10.2% in Europe (95% CI: 5.7–15.8) and 33.3% in North America (Table 2).

In total, 664 earrings parts intended to be inserted into the pierced skin were tested (Table S8). The publication dates ranged from 2011 to 2020. Three studies from Europe [39, 40, 41] and one from Turkey [51] reported on nickel release from earring post assemblies/studs. The pooled proportion of EN1811 tested earrings that exceeded 0.2 μg Ni/cm2/week was 24.7% in Europe (95% CI: 19.2–30.7) and 31.8% in Turkey (Table 2).

4. Discussion

The systematic review and meta‐analysis of 5333 individuals from the adult general population and 20 330 adult patients with dermatitis confirmed a significant association between piercings and nickel allergy (OR: 5.9 [95% CI: 3.6–9.4, p = < 0.0001] vs. OR: 3.6 [95% CI: 2.3–5.8]). Furthermore, 10.2% (95% CI: 5.7–15.8) of European earrings intended for prolonged skin contact and 24.7% (95% CI: 19.2–30.7) of European earrings intended for direct insertion into pierced skin exceeded the limits of the EU nickel restriction.

The fact, that the pooled ORs across the general population and dermatitis patients were comparable supports a consistent association between nickel allergy and piercing. Additionally, the pooled etiological fraction was 82% for adults in the general population (95% CI: 55.2%–92.8%) and 69.7% for adult dermatitis patients (95% CI: 62.7%–75.3%), indicating that an intervention addressing the risk of piercings is likely to have a significant reducing effect on the risk of nickel allergy.

Of interest, three Finnish studies reported higher ORs for the general population, which may be attributed to the predominance of female participants in these studies [20, 26, 30].

The increased risk of nickel allergy when pierced may be due to increased nickel exposure caused by the stratum corneum being removed during the piercing procedure. Subsequently, reinserting pieces of piercing jewellery like earrings may create a micro‐trauma in the artificial skin canal, which may lead to sensitisation or elicitation. After epithelisation, the protection utilised by the artificial skin canal is unknown, and the risk of sensitisation/elicitation of nickel allergy may differ from that of untraumatized skin. Previous research has demonstrated an increase in the prevalence of nickel allergy with the number of piercings [55, 56]. However, a protective effect of orthodontic appliances such as braces containing nickel prior to the piercing procedure has been found in some studies [34, 57]. This is probably due to nickel tolerance that is induced through a systematic exposure through oral mucosa.

A notable finding of our study is the variation between European countries and non‐European countries in nickel release from earrings. Earrings in Europe generally release less nickel than those from Asia and North America, reflecting a positive impact of the EU nickel restriction. However, a substantial proportion of earrings in Europe still exceed the regulatory limits: 11.3% (95% CI: 7.9–15.2) of the earrings were DMG positive, while 24.7% (95% CI: 19.2–30.7) of the earring post assemblies/studs intended for piercing body parts and 10.2% (95% CI: 5.7–15.8) of the earrings intended for prolonged skin contact exceeded the limits as demonstrated by the EN1811 test. In contrast, over 30% of the earrings from Asia and North America had excessive nickel release. Alarmingly, 13% of the earrings in an Italian market survey sold as ‘nickel‐free’ released > 0.5 μg Ni/cm2/week [16]. These findings indicate that the EU nickel restriction has led to a decrease in nickel release from earrings in the European market, although there is a strong need for improved compliance. To reduce the nickel release from earrings in other parts of the world, it is suggested that restrictions similar to the EU nickel restriction are implemented worldwide. Test methods for detecting nickel release include the dimethylglyoxime (DMG) spot test [47] and the EN1811 [58]. The EN1811 test is the European standard reference method for nickel release which is used to ensure compliance with the EU nickel restriction. This method is complex, expensive, and time‐consuming [58]. The DMG spot test has modest sensitivity and high specificity but is only able to detect nickel release > 0.5 μg Ni/cm2/week [42, 47]. The majority of studies of nickel release from earrings use the DMG spot test. It may be beneficial for the DMG spot test to be used for legislative purposes, as it was suggested in our letter to the editor of Contact Dermatitis [59], although it is not possible to detect excessive nickel release from post assemblies with this test.

Most studies on elicitation of allergic nickel dermatitis investigate either single or repeated exposure to nickel on skin or pre‐irritated skin. The study that provides the evidence of support for the nickel release limit of 0.5 μg Ni/cm2/week for the first nickel regulation in Denmark and the first EU nickel restriction was performed on nickel allergic dermatitis patients. It involved single, occluded nickel exposures for 48 h, applied to intact skin on the back [60]. Subsequently, the nickel release limit for post assemblies, including studs inserted into piercing holes, was set to 0.2 μg Ni/cm2/week. This may have been based on one study investigating the clinical reaction in 25 nickel‐allergic individuals after they were ear‐pierced with AISI 316L stainless steel post assemblies. The authors of the mentioned study concluded that this limit was safe for nickel‐allergic individuals, although two of the nickel‐allergic individuals developed itching and redness in the piercing area 48 h after exposure [61]. To our knowledge, no studies exist that investigate the deposition/release of nickel under actual use conditions of earrings. Even nickel doses within the regulatory limits can induce sensitisation, as low‐dose exposure may activate the immune system and generate localised immune memory [62]. Studies have shown that even AISI 316L stainless steel can release nickel, and stainless steel piercing kits can also elicit allergic nickel dermatitis [63, 64]. In addition, nickel release from stainless steel imbedded in blood plasma has been shown to be almost doubled compared to the release in artificial sweat [65]. This is of importance for potential nickel allergy during epithelisation after the piercing procedure. According to the piercing practitioners, the recommended materials for piercing studs are titanium, surgical steel, or glass [66].

A case study reported the presence of nickel fragments in a pierced earlobe 8 weeks after removal of a coated earring containing nickel. The earring had caused allergic nickel dermatitis, likely due to surface irregularities that increased nickel exposure [67]. This finding raises concerns about the durability of protective coatings on piercing jewellery like earrings. Although the EU nickel restriction mandates compliance of the earrings for 2 years, earrings are often used longer, potentially spanning generations. The current regulations therefore only protect wearers for a fraction of their anticipated usage time.

Regulatory actions have significantly reduced the prevalence of nickel allergy over the past decades. In Denmark, the prevalence of nickel allergy was markedly reduced in young women pierced after the regulation [68]. However, earrings remain the leading cause of allergic nickel dermatitis in nickel‐allergic patients, even among those presumed to be protected by the existing regulations [69]. Additionally, approximately 15 years after the implementation of the Danish nickel regulation in 1989 [70], the association between nickel allergy and hand eczema among young women declined significantly [71].

The continued high prevalence of nickel allergy among young individuals [31] suggests that the existing EU nickel restriction provides insufficient protection against the induction of nickel allergy and allergic nickel dermatitis. Our systematic review and meta‐analysis have demonstrated an increased risk of developing nickel allergy associated with piercings. This may be because the limit in the restriction of nickel release from earring post assemblies/studs is too high or because it is not complied with. Additionally, our review revealed that a significant proportion of earrings available on the market, both in European and non‐European countries, exceeds the limits of the EU nickel restriction. It appears that the limits of the restriction are not complied with, and that compliance testing by authorities, manufacturers, importers, and sellers of nickel‐containing items is not sufficient. A potential solution to this issue could be to prohibit the use of nickel in earring post assemblies/studs. This approach would address the problem of non‐compliance as well as the possibility that the current nickel release limit potentially is too high.

5. Limitations

The limitations of the study include the fact that more data from especially non‐European countries is needed for (i) and (ii). For (i), the day of the patch test reading and the way it was interpreted may be a limitation. The use of continuity correction three times in (i) could also introduce minor uncertainty in the individual and pooled OR. For (ii), not all studies specified the type of earring or the part of the earring that was tested. Earring clips may have unintentionally been included in the analysis. Another limitation in (ii) is the potential bias in the selection and purchase of earrings. The exact value for each tested earring was not consistently reported.

6. Conclusion

In conclusion, piercing poses a significant risk factor for nickel allergy, and a large proportion of earrings still release nickel in amounts that may result in nickel allergy and allergic nickel dermatitis. This study demonstrates that interventions aimed at reducing exposure to nickel through piercings have a major effect on the risk of nickel allergy. Stricter enforcement of existing regulations and consideration of new measures in both the EU and the rest of the world are essential.

Author Contributions

Benedikte von Spreckelsen: writing – original draft, writing – review and editing, methodology, data curation, formal analysis, conceptualization, investigation, validation, visualization, project administration. Mikkel Bak Jensen: data curation, formal analysis, methodology, conceptualization, investigation, writing – review and editing. Jeanne Duus Johansen: writing – review and editing, methodology, conceptualization, validation, supervision, visualization. Malin Glindvad Ahlström: writing – review and editing, visualization, validation, methodology, supervision, conceptualization.

Conflicts of Interest

The authors declare no conflicts of interest.

Supporting information

Data S1. Supporting Information.

COD-93-275-s001.docx (136.6KB, docx)

von Spreckelsen B., Jensen M. B., Johansen J. D., and Ahlström M. G., “Nickel Allergy and Piercings: A Systematic Review and Meta‐Analysis,” Contact Dermatitis 93, no. 4 (2025): 275–284, 10.1111/cod.14837.

Funding: This work was supported by the Danish Environmental Protection Agency under the Ministry of Environment of Denmark.

Data Availability Statement

The data that supports the findings of this study are available through the corresponding author.

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

Data S1. Supporting Information.

COD-93-275-s001.docx (136.6KB, docx)

Data Availability Statement

The data that supports the findings of this study are available through the corresponding author.

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