Looking back,and forward to 2015

Nickel‐containing alloys are widely used in orthodontic appliances, even though nickel is by far the most common contact allergen. However, the scientific evidence concerning allergic reactions to nickel in orthodontic patients has not been evaluated systematically. The objective of this study was to investigate whether the prevalence of nickel hypersensitivity is affected by orthodontic treatment. Unrestricted electronic and manual searches were performed until July 2013 for human clinical studies assessing orthodontic treatment and nickel hypersensitivity. Methodological limitations were evaluated with the Downs and Black tool. Crude and adjusted odds ratios (ORs) with their 95% confidence intervals (CIs) were calculated from random‐effects meta‐analyses, followed by subgroup and sensitivity analyses. Thirty studies were included in the review, and 24 datasets with 10 184 patients in the meta‐analyses. Orthodontic treatment had no significant effect on nickel hypersensitivity (n = 11; crude OR 0.99; 95%CI: 0.78–1.25; p = 0.914). However, when confounding from factors such as sex and piercings was taken into account, orthodontic treatment was associated with a lower risk of hypersensitivity (n = 1; adjusted OR 0.60; 95%CI: 0.40–0.80; p < 0.001). This was even more pronounced when orthodontic treatment was performed prior to piercing (n = 7; crude OR 0.35; 95%CI: 0.24–0.50; p < 0.001). Orthodontic treatment seems to have a protective role against nickel hypersensitivity, especially when it precedes piercings.     

The association between null mutations in the filaggrin gene and contact sensitization to nickel and other chemicals in the general population

Background It was recently shown that filaggrin gene (FLG) null mutations are positively associated with nickel sensitization. We have hypothesized that histidine‐rich filaggrin proteins in the epidermis chelate nickel ions and prevent their skin penetration and exposure to Langerhans cells. Furthermore, we have proposed that the low degree of genetic predisposition to nickel sensitization found by a Danish twin study was explained by a high prevalence of ear piercing among participants resulting in ‘bypassing’ of the filaggrin proteins. Objectives To investigate the association between FLG null mutations and (nickel) contact sensitization. Methods A random sample of 3335 adults from the general population in Denmark was patch tested and genotyped for R501X and 2282del4 in the FLG gene. Results The combined carrier frequency of FLG null mutations was 8·1%. Nickel, fragrance and contact sensitization to at least one allergen were not associated with FLG null mutations. A crude analysis on women who did not have ear piercings revealed a positive association between FLG null mutations and nickel sensitization [8·3% vs. 2·4%; odds ratio (OR) 3·71, 95% confidence interval (CI) 0·73–18·96] as well as between FLG null mutations and allergic nickel dermatitis (8·3% vs. 1·3%; OR 6·75, 95% CI 1·17–38·91). FLG mutation status and atopic dermatitis were positively associated with neomycin or ethylenediamine sensitization. Conclusions This study suggests that FLG null mutations may be a risk factor for the development of nickel sensitization. However, ear piercing was a much stronger risk factor in our general population and we could therefore identify a positive association only in women without ear piercings. Contact sensitization to specific chemicals is related to treatment exposure.     

Nickel sensitization in orthodontically treated and non-treated female adolescents

Background. The importance of the nickel exposure from fixed orthodontic appliances is under continuous discussion. Objectives. Our aim was to investigate nickel allergy and the risk of nickel sensitization among female adolescents during orthodontic treatment with fixed appliances as compared with non‐treated female adolescents. Subjects and methods. Female patients starting or with ongoing orthodontic treatment (n = 30) and young females without a history of orthodontic treatment (n = 140) were studied. Patch testing with 5% nickel sulfate was carried out twice on each participant with an approximately 1‐year interval. The subjects completed a questionnaire before the first testing. Results. None of the 7 orthodontic patients with a positive patch test reaction to nickel had any clinically visible intraoral allergic symptoms during their treatment. No significant difference was seen in the occurrence of positive nickel reactions in regard to orthodontic treatment, or between the first and second tests. In the treatment group, 2 patients changed from nickel‐positive to nickel‐negative during the observation period, and one patient showed an opposite change. The quantity and course of changes in the repeated nickel patch test reactions did not differ significantly between the subjects with and without orthodontic treatment experience. Conclusions. Nickel sensitization from orthodontic appliances is improbable, but nickel sensitization may develop also during orthodontic treatment.     

Nickel allergy and orthodontic treatment

OBJECTIVES: Tolerance induction to prevent development of nickel allergy has been suggested with permanent dental braces. We wanted to find out which effect orthodontic treatments had had on the development of nickel allergy in university students. STUDY DESIGN: We examined and patch tested 153 students, of whom 113 had a history of pierced skin, and 70 a history of orthodontic treatment roughly 10 years earlier. RESULTS: All except one student with pierced skin were females. Development of nickel allergy was significantly associated with skin piercing (54% compared with 12%). At the time of the study, there was a slight but non-significant difference in the prevalence of nickel allergy between students who had been subjects for orthodontic treatment (49%) compared with non-treated ones (58%) if they had pierced skin. There were no significant differences in the development of nickel allergy among students who had had permanent dental braces before (50%) or after skin piercing (48%). However, from 40 students without skin piercing four of 11 (three males) with a history of permanent braces had developed nickel allergy, as compared with none of 22 (P = 0.008) without orthodontic treatment suggesting possibility of sensitization through dental devices. CONCLUSIONS: Orthodontic treatment may not lead to tolerance induction on all occasions, and sensitization through permanent devices seems to be possible.     

Nickel sensitization in adolescents and association with ear piercing,use of dental braces and hand eczema. The Odense Adolescence Cohort Study on Atopic Diseases and Dermatitis (TOACS)

The prevalence of nickel allergy (sensitization) and the associations with ear piercing, use of dental braces and hand eczema were assessed in a cohort of 1,501 8th grade schoolchildren (aged 12-16 years) in Odense, Denmark. Nickel allergy was found in 8.6% and was clinically relevant in 69% of cases. Nickel allergy was found most frequently in girls and the association with ear piercing was confirmed. Application of dental braces (oral nickel exposure) prior to ear piercing (cutaneous nickel exposure) was associated with a significantly reduced prevalence of nickel allergy. In adolescents a significant association was found between hand eczema and nickel allergy. A follow-up study of this population is planned in order to assess the course and development of contact dermatitis, hand eczema and atopic diseases in adulthood and after choice of occupation.     

Nickel,cobalt and chromate sensitization and occupation*

Background: Exposure to nickel, cobalt and chromate are important causes of occupational contact dermatitis. Objectives: To estimate the prevalence of nickel, cobalt and chromate allergy in a population of consecutive patients and to investigate the possible association with individual and occupational risk factors. Patients/Methods: A total of 14 464 patients (67.6% women and 32.4% men) with suspected allergic dermatitis underwent patch tests. The associations between patch test results and occupations were studied by multivariate logistic regression analysis. Results: About 24.6% of the patients reacted positively to nickel sulphate, 10.2% to cobalt chloride and 8.7% to potassium dichromate. Nickel sensitization was higher in women aged 26–35 years in comparison with the youngest group (15–25 years) and the older group (> 45 years). In women, the prevalence of positive reactions to nickel was positively associated with metal and mechanical work (OR 1.54; 95%, CI 1.16–2.05). Chromate sensitization was more prevalent in building trade workers for both women (OR 1.58; 95% CI 1.00–2.49) and men (OR 2.24; 95% CI 1.55–3.22). Cobalt sensitization was associated with textile and leather work in women (OR 1.52; 95% CI 1.09–2.12) and with cleaning work in men (OR 1.86; 95% CI 1.18–2.93). Conclusions: Our study showed interesting associations between some occupations and nickel, chromate and cobalt allergy.     

Nickel Allergy and Our Children's Health: A Review of Indexed Cases and a View of Future Prevention

Nickel is the leading cause of allergic contact dermatitis (ACD) from early childhood through adolescence. Studies have shown that skin piercings and other nickel‐laden exposures can trigger the onset of nickel ACD in those who are susceptible. Nickel ACD causes a vast amount of cutaneous disease in children. Cases of nickel ACD in children have been reported in peer‐reviewed literature from 28 states. Common items that contain inciting nickel include jewelry, coins, zippers, belts, tools, toys, chair studs, cases for cell phones and tablets, and dental appliances. The diagnosis of nickel ACD has been routinely confirmed by patch testing in children older than 6 months suspected of ACD from nickel. Unlike in Europe, there are no mandatory restrictions legislated for nickel exposure in the United States. Denmark has demonstrated that regulation of the nickel content in metals can lower the risk of ACD and the associated health care–related costs that arise from excess nickel exposure. To further awareness, this article reviews the prominent role of nickel in pediatric skin disease in the United States. It discusses the need for a campaign by caretakers to reduce nickel‐related morbidity. Lastly, it promotes the model of European legislation as a successful intervention in the prevention of nickel ACD.     

Concurrent sensitization to metals and occupation

Background. Cosensitization to nickel, cobalt and chromium occurs in the general population and in some occupational groups. Objectives. To estimate the isolated and concurrent occurrence of nickel, cobalt and chromium contact sensitization and their association with individual and occupational risk factors. Patients/methods. Twelve thousand four hundred and ninety‐two patients were patch tested with the European baseline series between 1997 and 2004 in north‐eastern Italy. The associations between patch test results and patient characteristics and occupations were investigated by means of multinomial logistic regression analysis. Results. Of the patients, 34.7% (4334 patients) had one or more positive patch test reactions to metals. As compared with those with negative reactions to all three metals, nickel sensitization was significantly higher in females than in males, not only as monosensitization, but also as cosensitization with cobalt, with chromium, or with both metals. Building and related trades workers showed positive reactions to chromium + nickel [odds ratio (OR) 1.99; 95% confidence interval (CI) 1.05–3.76) and chromium + cobalt (OR 2.61; 95% CI 1.46–4.67]. Cleaning workers showed a high prevalence of nickel, chromium, nickel + chromium and nickel + cobalt + chromium cosensitization (ORs 1.29, 1.66, 2.11, and 1.79, respectively). An excess risk for cosensitization to all three metals was found in textile and leather workers (OR 2.19; 95% CI 1.10–4.33), and in bartenders (OR 2.10; 95% CI 1.03–4.26). Conclusions. Some occupational groups are more likely to develop nickel, cobalt and chromium cosensitization.     

The association between hand eczema and nickel allergy has weakened among young women in the general population following the Danish nickel regulation: results from two cross‐sectional studies

Background: An association between nickel contact allergy and hand eczema has previously been demonstrated. In 1990, Denmark regulated the extent of nickel release in the ear‐piercing process as well as nickel release from consumer products. Objectives: This study aimed to evaluate the effect of the Danish nickel regulation by comparing the prevalence of concomitant nickel allergy and hand eczema observed in two repeated cross‐sectional studies performed in the same general population in Copenhagen. Materials: In 1990 and 2006, 3881 18–69 year olds completed a postal questionnaire and were patch tested with nickel. Data were analysed by logistic regression analyses and associations were expressed as odds ratios (ORs) with 95% confidence intervals (CIs). Results: The prevalence of concomitant nickel contact allergy and a history of hand eczema decreased among 18–35‐year‐old women from 9.0% in 1990 to 2.1% in 2006 (P < 0.01). The association between nickel contact allergy and a history of hand eczema decreased in this age group between 1990 (OR = 3.63; CI = 1.33–9.96) and 2006 (OR = 0.65; CI = 0.29–1.46). Among older women, no significant changes were observed in the association between nickel contact allergy and hand eczema. Conclusions: Regulatory control of nickel exposure may have reduced the effect of nickel on hand eczema in the young female population.     

p-Phenylenediamine sensitization and occupation

Background. p‐Phenylenediamine (PPD) is an extreme delayed‐type skin sensitizer, and is relevant in both occupational and non‐occupational exposures. Objectives. To estimate the prevalence of PPD sensitization in a population of consecutive patients with suspected allergic contact dermatitis who attended units of dermatology or occupational medicine in north‐eastern Italy and to investigate the association between their PPD sensitization and occupation. Patients/Materials/Methods. A total of 14 464 patients (67.6% women and 32.4% men) with suspected allergic dermatitis underwent patch testing. The associations between patch test results and occupations were studied by multivariate logistic regression analysis. Results. In both sexes, PPD sensitization was significantly associated with hairdressing and beauty occupation [women, odds ratio (OR) 6.58, 95% confidence interval (CI) 3.76–11.50; men, OR 22.3, 95% CI 4.18–119]. In the female group, PPD sensitization was also significantly higher in professional drivers (OR 5.31, 95% CI 1.76–16.1), barmaids (OR 1.89, 95% CI 1.04–3.44), and cleaners (OR 1.82, 95% CI 1.24–2.68). In the male group, PPD sensitization was significantly higher in bakers and waiters (OR 13.0, 95% CI 1.38–123), household workers (OR 8.46, 95% CI 1.68–42.8), and printers (OR 5.68, 95% CI 1.50–21.5). Conclusions. Our study showed that workers in several occupations may be at higher risk of developing sensitization to PPD. It is of importance to reduce possible exposure to PPD‐crossreacting substances in these occupations.     

Lifestyle and nickel allergy in a Swedish adolescent population: effects of piercing, tattooing and orthodontic appliances

The aim of this study was to estimate the prevalence of life-style practices in adolescents and their association with nickel allergy. Upper secondary school pupils (n?=?4,376; 15-23 years) were patch-tested for nickel aller-gy, follow-ing completion of a questionnaire (answered by?6,095). Almost 86% girls and 21% of boys reported piercing. More girls (6%) than boys (3%) had a tattoo. Twenty-six percent of the girls and 18% of the boys were regular smokers. Vegetarian/vegan diets were reported by 20% of girls and by 6% of boys. Piercing, female gender, and vocational programme increased the risk of nickel allergy, whereas orthodontic appliance treat-ment prior to piercing reduced the risk of nickel allergy. Pupils in vocational programmes had the highest prevalence of nickel allergy. Lifestyle behaviours are interconnected and cluster in subgroups of adolescents. Female sex, piercing and choice of educational programme are prominent lifestyle markers. A trend shift is observed, where more girls than boys report tattooing.     

Allergic contact sensitization in the general adult population: a population-based study from Northern Norway

Few studies have so far addressed the prevalence and risk factors for contact sensitization in the general adult population; however, many such studies have been conducted in hospitals. We present the prevalence of contact sensitization in a general adult population and its relationship to potential risk factors like smoking, ear piercing and atopic diseases. 1236 adults (44.2% men and 55.8% women) were randomly selected from a cross-section of the population in Sør-Varanger municipality, Norway, and patch tested with TRUE Test (Pharmacia, Hillerød, Denmark). Contact sensitivity to at least 1 out of 24 allergens was found in 35.4% of the women and in 14.8% of the men. The most common allergens were nickel (17.6%), cobalt (2.8%), thiomersal (1.9%), fragrance mix (1.8%) and colophony (1.2%). All other allergens were observed in 1.0% or less. In women, ear piercing was an important risk factor for nickel sensitization. No such significant correlation was seen in men [in women relative risk (RR) = 3.30, 95% confidence interval (CI) = 2.01–5.43, and in men RR = 1.82, 95% CI = 0.66–5.00], and contact sensitivity was associated with atopic dermatitis (AD) [adjusted odds ratio (OR) = 1.58, 95% CI = 1.04–2.40] and smoking (adjusted OR = 1.42, 95% CI = 1.01–1.99) in women but not in men. The prevalence of contact sensitivity was common in this general population, especially in women. Smoking and AD might be a risk factor for contact sensitization.     

Nickel reactivity and filaggrin null mutations--evaluation of the filaggrin bypass theory in a general population

Background. It was recently shown that filaggrin null mutation carrier status was associated with nickel allergy and self‐reported intolerance to costume jewellery. Because of the biochemical characteristics of filaggrin, it may show nickel barrier properties in the stratum corneum. Objectives. To investigate whether subjects with filaggrin null mutations report nickel dermatitis at an earlier age than wild‐type individuals, and to analyse whether null mutation carriers have stronger patch test reactivity to nickel sulfate than do wild‐type individuals. Materials. A total of 3471 Danes (18–69 years of age) answered a questionnaire about general health, and underwent patch testing and filaggrin genotyping. Results. The mean number of years at risk of developing nickel dermatitis was significantly lower for the filaggrin null genotype than for the wild‐type genotype when ear piercing status was considered. In positive patch test readings, the proportion of null mutants increased with increasing reaction strength. Conclusions. Filaggrin null mutations may lower the age of onset of nickel dermatitis. The hypothesis that ear piercings obscure the effect of filaggrin null mutations on the development of nickel allergy in statistical analyses was supported. An association between the null genotype and increased nickel sensitivity was indicated by patch test reading and questionnaire data.     

Lifestyle factors and hand eczema in a Swedish adolescent population

Background: Hand eczema risk factors are potentially associated with lifestyle, and changes in lifestyle may influence the prevalence of this condition. Objectives: To report potential lifestyle risk factors and their association with hand eczema. Patients/Materials/Methods: Cross‐sectional questionnaire survey and standard patch test among Swedish upper secondary school children. The participation rate was 81% (6095/7543) for the questionnaire and 59% (4439/7543) for the test. Results: Girls reported piercing (84% versus 18%), tattooing (6% versus 3%), smoking (24% versus 16%) and vegetarianism (21% versus 7%) significantly more often than boys. Girls had significantly more hand eczema (7% versus 4%) than boys. Besides female sex (OR 2.0), allergic rhinitis (OR 1.8), flexural eczema (OR 4.5), and positive nickel test (OR 1.7) were significant risk factors in multivariate analysis. Piercing entailed a decreased risk (OR 0.6). Other lifestyle practices had no association with hand eczema. Vegetarian diet and dental braces which potentially increase oral nickel exposure were not associated with hand eczema prevalence in nickel sensitized individuals. Conclusions: The studied lifestyle practices were more prevalent in girls. Smoking, tattooing, and diet were not associated with the occurrence of hand eczema.     

Contact sensitization to common haptens is associated with atopic dermatitis: new insight

Background It has been much debated whether atopic dermatitis (AD) is associated with contact sensitization as past findings have been conflicting. A positive association might change our clinical practice. Objectives To investigate the association between AD and contact sensitization taking the likely route of allergen exposure into account. Methods Questionnaire and clinical data from a cross‐sectional study performed in a general population in Copenhagen. In total, 3202 adults aged 18–69 years were patch tested, filaggrin genotyped for 2282del4 and R501X and questioned about AD. Results The variable ‘contact sensitization to at least one allergen, but not nickel and thimerosal’ was significantly associated with AD (odds ratio 2·53, 95% confidence interval 1·59–4·04). The higher prevalence of contact sensitization was driven mainly by fragrance chemicals. In a subanalysis in nonpierced women, a positive association was also found for nickel sensitization. Nickel and thimerosal sensitization may introduce bias in data analysis as these allergies often develop following skin piercing where the skin compartments are bypassed. Conclusions We suspect that individuals with self‐reported AD from this study mainly had mild disease. However, clinicians should be aware of increased levels of contact sensitization in individuals with AD. Patch testing should therefore be considered at an early point in individuals with a history of AD and active disease. The fundamental relationship between atopic disease and environmental chemical exposure may be of a more complex and intimate nature than previously supposed.     

Prevalence of nickel allergy among Finnish university students in 1995

Nickel allergy was studied in a sample of 1st-year university students starting their studies in 1995. A total of 296 subjects (72%) of 413 invited participated in the clinical examination, and 284, 96 male and 188 female, were patch tested (69%). A history of nickel sensitization was enquired for. Prick tests and serum specific IgE levels were determined. Occurrence of atopic dermatitis, hand eczema, and current exposure to metals were recorded. Nickel allergy was encountered in 39% of all female students, in 42% of females with pierced skin, and in 14% of females without pierced skin. The corresponding figures for males were 3%, 7% and 3%. In the multiple regression analysis, the risk factors for nickel allergy were female sex (OR 8.1, p<0.01), current metal exposure at examination (OR 4.1, p<0.01) and skin piercing (OR 3.6, p<0.05). Positive prick tests or elevated IgE levels to common allergens were not significantly associated with nickel allergy. In female students, the prevalence of nickel allergy has increased from 13% in 1986 to 39%. The prevalence among males has remained low at 3%. The results indicate that, in addition to skin piercing, current metal contacts are important risk factors for nickel allergy. This finding gives support to the EU Nickel Directive.     

Risk assessment for nickel contact allergy

Nickel is one of the most common allergens causing allergic contact dermatitis worldwide. The aim of the study was to evaluate the contributing factors to nickel contact allergy (NiCA) in Asians who have a unique culture and lifestyle. We randomly selected 324 previously patch‐tested patients, 162 nickel patch test (PT)‐positive patients and 162 nickel PT‐negative patients. The patients were telephone interviewed for their lifestyle information. Most of the nickel PT‐positive patients (93.2%) were female with a mean age of 38.9 ± 13.3 years compared with the other group of nickel PT‐negative patients who had a smaller proportion of females (76.5%) with an older mean age of 44.1 ± 14.9 years (P = 0.001). Multivariate analysis was able to establish that the significant risk factors for NiCA were female sex (odds ratio [OR], 6.38; 95% confidence interval [CI], 2.15–18.94), young age (OR, 0.98; 95% CI, 0.96–1.00), occupation with long periods of exposure to metal (OR, 3.08; 95% CI, 1.18–8.02), seafood (OR, 1.96; 95% CI, 1.17–3.27) and canned food consumption (OR, 3.12; 95% CI, 1.17–8.33) (P < 0.05). The adjusted factors found to associate with NiCA were female sex, young age, occupation with long periods of exposure to metal, seafood and canned food consumption.     

Nickel sensitization and ear piercing in an unselected Danish population

The study aimed at evaluating nickel sensitization and ear piercing in an unselected population. A questionnaire and ready-to-apply patch tests (TRUE-Test) were mailed to 793 subjects, aged 15 to 69 years. A total of 567 (71.5% out of the 793) were patch tested. The tests were read 2 days after application. Nickel sensitization was diagnosed in 11.1% of the females and in 2.2% of the males. Independent of sex, old age was associated with a lower risk of nickel sensitization ( p <0.01). The risk of nickel sensitization was independent of a history of flexural eczema ( p >0.5). Ear piercing was more common in the young than in the older age groups, ranging from 30.5% to 0.0% in men, and from 91.5% to 42.9% in women, Sensitization lo nickel was found in 14.8% of those with pierced ears as compared to 1.8% among those without pierced ears. When adjusted for the effects of sex and age, the risk of nickel sensitization among those with pierced ears remained significantly increased and the odds ratio value was 4.5: the 95% confidence interval of the odds ratio value was 1.5 to 13.0. The study confirmed that nickel sensitization in the general population is common, particularly among women. Ear piercing is probably an important risk factor for nickel sensitization.     

Body Piercing

Body and earlobe piercing are common practices in the USA today. Minor complications including infection and bleeding occur frequently and, although rare, major complications have been reported. Healthcare professionals should be cognizant of the medical consequences of body piercing. Complications vary depending on the body-piercing site, materials used, experience of the practitioner, hygiene regimens, and aftercare by the recipient. Localized infections are common. Systemic infections such as viral hepatitis and toxic shock syndrome and distant infections such as endocarditis and brain abscesses have been reported. Other general complications include allergic contact dermatitis (e.g. from nickel or latex), bleeding, scarring and keloid formation, nerve damage, and interference with medical procedures such as intubation and blood/organ donation. Site-specific complications have been reported. Oral piercings may lead to difficulty speaking and eating, excessive salivation, and dental problems. Oral and nasal piercings may be aspirated or become embedded, requiring surgical removal. Piercing tracts in the ear, nipple, and navel are prone to tearing. Galactorrhea may be caused by stimulation from a nipple piercing. Genital piercings may lead to infertility secondary to infection, and obstruction of the urethra secondary to scar formation. In men, priapism and fistula formation may occur. Women who are pregnant or breastfeeding and have a piercing or are considering obtaining one need to be aware of the rare complications that may affect them or their child. Though not a 'complication' per se, many studies have reported body piercing as a marker for high-risk behavior, psychopathologic symptoms, and anti-social personality traits. When it comes to piercing complications, prevention is the key. Body piercers should take a complete medical and social history to identify conditions that may predispose an individual to complications, and candidates should choose a qualified practitioner to perform their piercing. As body piercing continues to be popular, understanding the risks of the procedures as well as the medical and psychosocial implications of wearing piercing jewelry is important for the medical practitioner.     

Does early life exposure to antibiotics increase the risk of eczema? A systematic review

A number of studies have suggested that early life exposure to antibiotics can lead to an increased risk of developing eczema. This systematic review and meta‐analysis of observational studies, involving children or young adults aged 0–25 years, assessed the impact of antibiotic exposure either in utero or during the first 12 months of life on subsequent eczema risk. Twenty studies examined the association between prenatal and/or postnatal exposure to antibiotics and development of eczema. The pooled odds ratio (OR) for the 17 studies examining postnatal antibiotic exposure was 1·41 [95% confidence interval (CI) 1·30–1·53]. The pooled OR for the 10 longitudinal studies was 1·40 (95% CI 1·19–1·64), compared with a pooled OR of 1·43 (95% CI 1·36–1·51) for the seven cross‐sectional studies. There was a significant dose–response association, suggesting a 7% increase in the risk of eczema for each additional antibiotic course received during the first year of life [pooled OR 1·07 (95% CI 1·02–1·11)]. Finally, the pooled OR for the four studies relating to antenatal exposure was 1·30 (95% CI 0·86–1·95). We conclude that exposure to antibiotics in the first year of life, but not prenatally, is more common in children with eczema.