Relevant Contact Allergy Found in 41% of Hand Eczema Referred for Testing

Preservatives restricted in European cosmetics a decade ago, chromate that was meant to be out of cement, and the acrylates behind a booming nail industry are all still turning up on the hands of patients who cannot get their eczema under control. Among 1267 Portuguese patients with chronic hand eczema (CHE) referred for patch testing over 3 years, 57% reacted to at least 1 baseline allergen and 41% had a reaction judged currently relevant to their disease.¹

A Common Disease With a Contested Cause

Hand eczema carries a lifetime prevalence of about 14.5% with an incidence of 7.3 cases per 1000 person-years in the general population, occurs 1.5 to 2 times more often in women than men, and typically begins in the early to mid-20s.² More than a third of cases are moderate or severe, and roughly a third of affected individuals have a history of atopic dermatitis.

Where the disagreement sits is causation. Irritant contact dermatitis, allergic contact dermatitis, protein contact dermatitis, and atopic dermatitis all feed into CHE and frequently overlap, which makes patch testing the practical tool for deciding whether allergen avoidance belongs in the treatment plan at all.¹

Three Years of Testing Across Portuguese Referral Centers

The multicenter retrospective observational study drew on patch test results recorded between 2021 and 2023 at dermatology departments affiliated with the Portuguese Contact Dermatitis Research Group, located in the north, center, and south of the country and serving as referral centers for hospitals without contact dermatitis units. Testing followed European Society of Contact Dermatitis recommendations using the Portuguese baseline series, often supplemented with additional series and patients' own products.

Of 2980 patients tested across the 3 years, 1267 (43%) had CHE, of whom 391 were male and 876 female, with a median age of 42 years. The comparison group of 1713 patients without CHE was older, at a median 50 years (P < .001). Occupational cases made up 40.1% of the CHE group (n = 508), whereas 378 patients (29.8%) had current or past atopic dermatitis.

Occupational Cases Reacted Far More Often

Patients with CHE were significantly more likely than those without to have at least 1 positive reaction, at 57% vs 47% (P < .001; OR, 1.483). Nickel sulfate was the most frequent allergen at 22.1%, followed by cobalt chloride (7.2%), methylisothiazolinone (7.1%), fragrance mix I (6.3%), and 2-hydroxyethyl methacrylate, or HEMA (6.3%). Frequency and relevance diverged sharply, however: only 36.5% of nickel reactions were judged currently relevant, against 97% for thiuram mix, 95.7% for methylchloroisothiazolinone/methylisothiazolinone, 90.9% for methylisothiazolinone, and 84.5% for HEMA.

The occupational split was the study's most striking result. Among occupational cases, 74% had at least 1 positive reaction compared with 46% of non-occupational cases (P < .001; OR, 3.366). Current relevance was higher in the occupational group for potassium dichromate (72.7% vs 40.0%; P = .002), benzisothiazolinone (72.4% vs 36.8%; P = .015), cobalt chloride (55.1% vs 30.6%; P = .008), and nickel sulfate (35.4% vs 24.9%; P = .032). Fragrances ran the other way, with fragrance mix I relevant in 68.9% of non-occupational cases vs 43.2% of occupational ones (P = .009).

Patients with atopic dermatitis were not more likely to react overall, at 55% vs 58% in the non-atopic group (P = .315). HEMA and thiuram mix were actually more common in non-atopic patients, whereas methylisothiazolinone (P = .016) and Myroxylon pereirae (P = .029) were more often judged relevant among atopic ones.

A Referral Gap and Other Caveats

Fewer than 30% of the CHE cohort had atopic dermatitis, a proportion the investigators read as a referral pattern rather than a biological one. Hand involvement is common in atopic dermatitis, so a low referral rate points to testing that is not being ordered rather than an allergy that is not present.

“This finding may reflect that most physicians probably do not consider allergic contact dermatitis as a possible concomitant factor in atopic CHE,” the authors wrote, pointing to prior reports showing the same underuse of testing in atopic patients.

Because the study was retrospective and multicentric, it lacked the clinical detail needed to characterize CHE subtypes, and its population consists only of patients a dermatologist already suspected of contact allergy, a referral bias that inflates the apparent prevalence of allergic contact dermatitis relative to CHE generally. Prick and prick-prick testing, which is required to identify protein contact dermatitis, was not included, and occupational sector data were not collected, limiting interpretation of the occupational findings.

Even so, the relevance data carry a workable message for clinicians managing refractory hands: reaction frequency and clinical relevance are not the same measure, and the allergens worth chasing in a working patient are largely not the ones worth chasing in someone whose exposure is domestic.

References

1. Martins AA, Almeida P, Lobo I, Brasileiro A, Figueiredo C, Gonçalo M. Patch testing in chronic hand eczema: a multicentre study in Portugal. Contact Dermatitis. 2026;95(3):295-300. doi:10.1111/cod.70186

2. Quaade AS, Simonsen AB, Halling AS, Thyssen JP, Johansen JD. Prevalence, incidence, and severity of hand eczema in the general population - a systematic review and meta-analysis. Contact Dermatitis. 2021;84(6):361-374. doi:10.1111/cod.13804