Both eczema and urticaria are common skin diseases. Eczema is an umbrella term for a group of conditions in which the skin becomes red, itchy and inflamed in a characteristic pattern.1–3 There are different types of eczema: atopic dermatitis (AD), contact dermatitis, hand dermatitis and others,1–3 which can affect different anatomical areas of the skin.

Although eczema can appear at any time during life, about 60% of AD cases, for example, are thought to be present during the first year.4 Once the illness has occurred in the paediatric age, exacerbations may disappear or continue over the years. Approximately 40-60% of adult patients already experienced the disease in the past.5,6 However, few studies describe eczema epidemiologically in adults and the differences between prevalence definitions makes the comparison of results more complex, due to the methodological heterogeneity.

The prevalence of atopic eczema varies between 15-30% in children and 2-20% in adults, globally.7–9 A single study in Portugal reports a prevalence of atopic eczema in adults aged <15 years of 1.1%.10 However, the reasons for this variability are not known.8,9

Urticaria is a heterogeneous group of diseases. Almost all types of urticaria present with a common and distinctive clinical pattern, i.e., the development of itchy evanescent wheals and/or angioedema.11 The existing epidemiological data about the prevalence of urticaria, relate mostly, to the various subtypes of individual urticaria.

It is estimated that approximately 10-20% of the world's population will experience an episode of acute urticaria or angioedema at some point in life.7,12,13 Concerning the prevalence of general urticaria, around 15% of the population is affected worldwide.14

Both for eczema and urticaria, genetics is an important determinant of prevalence variability. Nevertheless, genetics is not alone. Other factors may influence, age and gender are reported to have an important role in the disease cycle.7,9,15–17

Due to the lack of information regarding prevalence of these diseases in Portugal, this study sought to determine the prevalence in the Portuguese adult population.

There is no listing or database in Portugal concerning the population studied. As so, telephone interviews were conducted in order to collect the data. The interviews were conducted in the last quarter of 2017 by a market research company: Consulmark®, certified by the International Standards Organization (ISO) 9001:2008. The interview was carried out with the person who answered the phone. This study was previously approved by the Portuguese commission of data protection (CNPD) in 2016.

All the individuals who answered and agreed to respond were included in the study. To calculate the prevalences, subjects were considered if:

They had current eczema or urticaria. In case of affirmative answer to the questions ‘Do you have atopic dermatitis or eczema or urticaria, confirmed by a doctor?’, and ‘Did you have the last symptom less than 5 years ago?’

Aged 16 years or more, having Portuguese nationality, and residing in Continental Portugal.

Individuals who, in the question “Who made the diagnosis” answered someone other than a health professional (a physician, a nurse or a pharmacist), were excluded. People with eczema included AD, contact dermatitis or hand eczema. People with urticaria included chronic or acute urticaria.

There is no data regarding the prevalence of these diseases in Portugal. For sample size purposes, we estimated a conservative average prevalence for both diseases together due to three factors: 1) because the prevalence in 6-7 and 13-14 years old is 14.1% and 12.7% respectively,18 2) the prevalence in adults is lower, and 3) the prevalence in the closest country, Spain, ranges 4-7%.6,19 The Portuguese population in the last quarter of 2017 was 10,047,621,20 and for an estimated 10% of prevalence, a margin of error less than 1% to improve precision and 95% confidence interval, a sample size of 4,267 was calculated. In this way we rounded off to 5000 phone calls.

The sample had a proportion that was approximately representative by population, region, gender, and age group with proximal distribution (Table 1). Although the percentages concerning age group were not as similar as expected, they are similar in terms of means: 48.70 vs 51.57, universe vs population, respectively.

Data were collected through a structured questionnaire consisting of eight questions developed specifically for the study objectives, covering topics such as gender, age, and region; number of people in household; having or not eczema or urticaria; time since diagnosis; who diagnosed; having the disease in childhood, and if another person in the family has the same disease.

Since the study was performed for two different diseases, the analyses were performed individually (having eczema or urticaria) and having at least one of these diseases. For prevalence purposes, the numbers of subjects with each disease were divided by the population who was interviewed by telephone.

The descriptive analyses were performed for qualitative variables (frequencies and percentages, with 95% of confidence interval) and quantitative variables (mean, median, standard deviation [SD], minimum, and maximum). The associations between prevalence and different regions, gender, and age group were made by chi-square test.

Odds Ratios with 95% CI were performed to measure associations with prevalences. Also, a multivariate analysis was executed with the following variables: disease (as dependent), age, region, and gender, with a 95% CI.

To infer about prevalence consistency, a secondary prevalence was computed by the sum of individuals in the households with disease divided by the sum of all households’ individuals. Therefore, the prevalence based on the number of individuals who answered the phone is designated “main primary prevalence”. The one that was calculated with households, is designated “secondary prevalence”.

Statistical tests were 2-tailed considering a significance level of 5%. Statistical analysis was conducted through the software IBM® SPSS® Statistics 22.

The population studied is not part of a set of observation units for which there is a listing or a data base in Portugal. Thus, to investigate the prevalence, the data collection was by telephone interviews. There are several studies in which the same methodology was used, namely a Portuguese study of the National Health Observatory in 2004, which objective was to evaluate the self-reported prevalence of certain chronic diseases, as psoriasis.21 As early as 1994, the use of telephone sampling was advocated for epidemiology and health-related research, usually based on random number generation.22 Prevalence studies for different diseases used a similar methodology,23–25 as well as in dermatology.19,26–28

Eczema represents a group of diseases with similar clinical characteristics, and there is not a clinical standard for the definition of the disease.28,29 In this study, our approach captured different subsets of the eczema and our definition of eczema, which was based on self-reported doctor diagnosed ‘eczema or atopic dermatitis’, might have resulted in an overestimation of the prevalence, not being possible to be exact of the AD prevalence. In this way, we are aware that is might be a limitation. The diagnosis of eczema and urticaria, when made by a non-dermatologist or a non-allergist physician is of doubtful reliability, although all patients confirmed having had a second medical opinion, we consider this as a limitation of the study.

The main prevalence in adult population of both diseases was found to be 4.4% of eczema and 3.4% of urticaria. With the secondary prevalences calculations we observed again that eczema was more prevalent than urticaria with similar prevalences in having at least one of the diseases (7.6%-7.9%). These are higher than findings in previous studies in Portugal and comparable to results from other countries. But comparisons among prevalence of eczema are affected by several drawbacks. Most studies presenting data of eczema prevalence have been focused on either several atopic diseases or the whole spectrum of skin diseases. Considerably fewer studies, especially among adults, have been focused on eczema. The questions about eczema have varied considerably from self-reports of itchy rash and ever having had eczema to point prevalence of physician examinations of the skin; the latter results in several-fold lower estimates of prevalence.30 As an example, Portugal has one study reporting eczema prevalence as 1.1%, although well designed and a representative sample, the number of interviews was less and it sought to investigate other allergic diseases prevalence.10 Comparing to the closest country, Spain, when we talk about the all eczema, the prevalence seemed to be similar to ours, 4.2%.6 In ascending order, we can find the following prevalences of eczema, Germany with 5,1%, Belgium with 5.9% and France with 8%,6 while AD prevalences seem to be 1.4%, 2%, 2.4% and 3.5%, respectively.6,19 There is evidence that in Switzerland adult prevalence of eczema is lower, 2.2%.6 Italy presents a 6.6-8.1% of eczema prevalence.6,28

According to Harrop et al., 2007, in Europe, atopic eczema is 0.14-0.60% of general eczema.6 In this way, we can estimate that prevalence of EA, in Portugal is around 0.61-2.64%.

Regarding urticaria, to our knowledge, there are very few studies with evidence of general urticaria prevalence. Germany has a prevalence of 8.8% and Norway 9% for urticaria throughout life, most of which is acute or physical.31 In Poland, an occurrence of 11.2% of urticaria was reported in the population over 15 years of age.14

The region where patients live represents a risk factor for several allergic diseases,15 and so the main prevalence was also evaluated by region, we found the Portuguese areas with more prevalence of eczema to be Lisbon e Vale do Tejo (5.5%) and Algarve (5.3%). Lisbon has a few characteristics known to possibly exacerbate eczema: it is the capital, it is very polluted, and has a lot of traffic. To further understand the difference observed in Algarve, more studies should be performed. Nevertheless, a study in Italy showed that the prevalence of eczema and AD was higher in Mediterranean area than in sub-continental, 8.5 vs 7.4 and 3.8 vs 2.8, respectively.28 On the other hand, prevalence of urticaria seems to be similar across the country.

As uniformly reported in the literature, eczema is more common amongst female than male subjects.6,9,17,32 We showed a female prevalence of 5.7% against 3.0% in the male population with eczema. Also, being a woman is a significant risk factor for eczema (OR 1.99), similar to OR reported in other studies 1.84,30 2.44,17 or 1.33.6 As for eczema, urticaria shows a higher prevalence in females.16,31,33,34 We observed a female prevalence of 4.2% vs 2.4% (in male). Being a woman is also a significant risk factor for urticaria (OR 1.73), similar to other studies (OR 1.46).14

We found that more than half of respondents (64.5% with eczema and 69% with urticaria) have had the disease for more than five years. Among those with eczema, we found that 64 patients (29.1%) had the disease during childhood, while in a self-reported study, 13.7% declare having had eczema in childhood.32 Among those with urticaria, 26 patients (15.5%) had the disease during childhood.

We calculated OR and adjusted OR for the variables age, gender, and region, finding similar results. From this we conclude that these variables can influence both diseases individually and that they do not interact with each other.

Family history is an important factor in these diseases,6 and we observed that of the 220 individuals with eczema, 40 (18.2%) reported having someone in their household with the disease as well. Of the 168 individuals with urticaria, 22 (13.1%) reported having someone in their home with the disease. A limitation of our study is the fact we did not collect data on variables such as race or job, which could help us to understand better the influence of family history.

With households’ results, we were able to calculate a secondary prevalence. However, in contrast to the main prevalence of the study, this step was calculated with adult and child populations. This is due to the way the data were collected. Additionally and also in contrast to the main prevalence of the study, the sample of secondary prevalence was not proportionally representative. Thus, a direct comparison is not possible. Nevertheless, the difference between them is not so great.

This study contributes with new data for the areas of Dermatology and Immunology in Portugal.

The prevalences found are higher than in previous studies in Portugal and comparable to results from other countries. Comparisons among prevalence of eczema are affected by several obstacles. Regarding urticaria, our results seem to be in the same line as others. Although there is only a few studies about prevalence of general urticaria. Being female with eczema and urticaria is more common and represents a higher risk factor than male subjects.

This study was funding by LEOPharma.