Contact dermatitis affects up to 20% of the population1 and is a common reason for visiting the dermatologist. Allergic contact dermatitis may be clinically indistinguishable from irritant contact dermatitis and endogenous contact dermatitis. Therefore, patch testing is essential when confirming a diagnosis.2 Patch tests group allergens in series according to the type of exposure.3 The standard series brings together the allergens that most frequently lead to sensitization, either at the national or the international level.4,5 Contact dermatitis guidelines recommend using the standard series—in our case, the Spanish standard series—on all patients who undergo patch testing, which should be completed with specific series.

In Spain, the Spanish Contact Dermatitis and Skin Allergy Research Group (Grupo Español de Investigación en Dermatitis de Contacto y Alergia Cutánea [GEIDAC]) has been responsible for creating and updating the Spanish standard series for more than 40years.4,6 This dynamic series is updated according to the frequency of sensitization to allergens assessed by GEIDAC. The most recent update was in 2016. This included methylisothiazolinone, diazolidinyl urea, and imidazolidinyl urea and removed clioquinol, thiomersal, mercury, and primin.6 It was previously modified in 2012 by replacing Euxyl K400 with methyldibromo glutaronitrile. Also added were phenoxyethanol, primin, fragrance mix II, and lyral,7 with respect to the previous modification in 2001, when Euxyl K400, budesonide, and tixocortol pivalate were added.

Given that it is impossible and ethically questionable to perform patch testing on the whole population, almost all epidemiology studies are based on the frequency of sensitization in patients assessed in contact dermatitis units.8,9 Obviously, this epidemiological approach assumes that the data may not be homogeneous and will differ according to the center they come from. The MOAHLFA index (Male, Occupational dermatitis, Atopy, Hand, Leg, Face, Age>40) for each study population can be used to determine whether samples from different geographical areas are comparable. This indicator expresses in percentage terms the epidemiological characteristics of the study population that could affect the results of patch testing a priori.10,11

The frequency of sensitization reported for allergic contact dermatitis caused by allergens from the standard series varies depending on the population that visits the unit, the selection criteria set for patch testing patients, and the percentage of patients treated for occupational exposure.3 Complejo Hospitalario Universitario Insular Materno Infantil (CHUIMI) belongs to the Health Service of the Canary Islands and is the dermatology reference center for south Gran Canaria. The center serves a population of around 400000 persons, many of whom work in the tourist industry.

Given that the description and the epidemiological follow-up of the sensitizers found in each unit represent the most valid approach for determining the main types of sensitization,3 we believe the results of CHUIMI should be reviewed over a long period. Similarly, data analysis is one of the main quality assurance criteria in our unit. The objective of the present study was to analyze the results for the Spanish standard series at CHUIMI from 2005 and 2018 and to compare them with widely available public data and data from other centers.6,12,13

We performed a retrospective descriptive study using the database of the Contact Dermatitis Unit of the Dermatology Department of CHUIMI, Las Palmas de Gran Canaria, Spain and Access Office, Version 2007. The study was approved by the Research Ethics Committee of the Canary Islands Health Service on April 7, 2020. The data collected were age, sex, personal history of atopic dermatitis, site affected, profession, positive readings at 96hours, and relevance of the positive findings.

We included patients who underwent patch testing with the standard Spanish series between January 2005 and June 2018. Patch testing was with the True Test series (SmartPractice Denmark ApS) and additional allergens according to the GEIDAC guidelines.6,13 Thereafter, testing was with the Spanish standard series from Allergeaze (MartiTor Alergia S.L.). The allergens from the last update of the standard series were used from January 1, 2016 onward. In order to ensure continuity over time, Euxyl K400 and methyldibromo glutaronitrile were considered statistically similar, as were quinoline mix and clioquinol.

The patch tests were performed according to the guidelines of the European Society of Contact Dermatitis (ESCD).2 Readings were taken at 48 and 96hours in all cases, and a late reading was taken in patients suspected of having allergy to corticosteroids. Patients were asked to return at 168hours if they developed late positive results. We took into account positive results (+, ++, or +++), and relevance was established based on the patient's symptoms and history of allergen exposure.

In the statistical analysis, we used the Pearson χ2 test to compare proportions and calculated the 95% CI for the difference in proportions. P values<.05 were considered statistically significant. Age and sex were adjusted for the scale of the European Surveillance System on Contact Allergies, as follows: woman aged under 40years, 32.5%; woman older than 40years, 32.5%; man under 40years: 32.5%; and man older than 40years, 32.5%. The statistical analysis was performed using R Core Team 2020, Version 4.0.2.

We included 1568 patients, of whom 71.6% were women. Few patients had occupational dermatitis or atopy (Table 1).

The most frequent sensitizations were for nickel (36.5%), methylchloroisothiazolinone/methylisothiazolinone (MCl/MI) (11.9%), methylisothiazolinone (11.8%), paraphenylenediamine (7.5%), and potassium dichromate (6.3%). These allergens were also associated with the highest frequency of present relevance. The positive results and relevance are shown in Table 2. Given the variability in the criteria used to assign relevance, this parameter was not taken into consideration for the discussion of the most frequent allergens.

Fig. 1 shows changes in sensitization to the 5 most common allergens over time.

Figure 1.

Positive results to nickel, methylchloroisothiazolinon/methylisothiazolinone (MCl/MI), methylisothiazolinone (MI), paraphenylenediamine (PPD), and potassium dichromate.

(0.21MB).

Our study showed the frequency of sensitization to allergens from the Spanish standard series among the population of the south of Gran Canaria, an island that is characterized by a subtropical climate, European population, and a local economy based on the tourist industry.

Our search of the Spanish medical literature revealed 3 studies that analyzed the Spanish series during the same period: 1 performed in Marbella between 2005 and 201012 and 2 multicenter studies performed in 200813 and 2012.6 It is important to note that the population of the latter multicenter study includes the patients assessed in the present study. A key finding of these studies was the greater frequency of sensitization in the sample from CHUIMI. This is more noticeable for the most common allergens, such as nickel, MCl/MI, methylisothiazolinone, and paraphenylenediamine (Table 3). The difference in the percentage of patients sensitized could be explained by epidemiological differences in the MOAHLFA index (Table 4), especially the higher percentage of women in the sample studied, which increases the frequency of sensitization for most of the allergens.1 Another epidemiological peculiarity of the study population is that many people work in the tourist sector—with high seasonal variations in winter—and the care provided is for common illnesses in the Canary Islands Health Service. The greater frequency of “block” sensitization could also be explained by the working method14 of the Dermatology Department of CHUIMI, where new histories are taken irrespective of whether the referral is by a dermatologist or other specialist, with patch testing recommended at the discretion of the person in charge of the unit. Therefore, we calculate that two-thirds of the patients referred eventually undergo patch testing. However, the high percentage of patients with a positive result and the low percentage of patients with present relevance are striking (Table 5).

Given that a contact allergen is included in the standard series if its frequency of sensitization is greater than 0.5%–1%,3,6 the data reported by CHUIMI support the 2016 update of the Spanish standard series, highlighting methylisothiazolinone and fragrance mix II, which are in the “top 10” of the updated series. Similarly, it seems reasonable to include lyral (2%), but not diazolinidyl urea, imidazolidinyl urea, or phenoxyethanol, whose frequency in the present study was 0.4%. As for the allergens removed from the series, the elimination of clioquinol seems justified. Both thiomersal and mercury had a high frequency of sensitization; however, they were withdrawn from the standard series because they have been prohibited in Europe since 2005 and have scarce clinical relevance. Primin was withdrawn because it is infrequent in Spain.6

Below, we discuss the 5 most common allergens in the series: nickel, MCl/MI, methylisothiazolinone, paraphenylenediamine, and potassium dichromate.

First, this study was performed at a single center, and the relevance of the allergens was determined based on the clinical history.

Second, it is difficult to compare data between the different studies owing to the lack of studies performed during the same period in the Spanish medical literature and the absence of publicly available data on the distribution of the working population by province.

Lastly, it is important to remember that changes in the composition of the Spanish standard series in 2012 and 2016 mean that certain allergens were only assessed during specific parts of the study period.

Findings for the allergens analyzed in the present series are increasingly consistent with those for the allergens that most frequently lead to sensitization in Spain, especially, nickel, MCl/MI, methylisothiazolinone, and paraphenylenediamine.

The authors declare that they have no conflicts of interest.