Childhood eczema: disease of the advantaged?

Subjects and methods

The national child development study developed from the national perinatal mortality survey,8 which gathered detailed information on over98% of babies born in England, Wales, and Scotland during the week of 3-9 March 1958. These babies have been followed up at the ages of 7, 11, 16, 23, and 33 years. Of the 9518 children for whom information was gathered at the ages of 7, 11, and 16, only those with complete responses on the presence or absence of visible eczema at these ages were included in this study (n = 8279, 87%).

When the children were aged 7 parents were asked by health visitors using a structuredquestionnaire whether their child had had eczematous rashes during the first year of lifeor at any time after the first year. When the children were aged 11 or 16, parents were sked whether they had had eczematous rashes in the past 12 months. We have used the term examined eczema to refer to visible eczematous dermatoses recorded by experienced school medical officers during a complete physical examination at the ages of 7, 11, and 16. Examination of the skin was part of a more general examination including physical and mental development. No hypothesis on skin disease was being tested by the study. We derived social class using the registrar general's classification according to the father's occupation when the childen were aged 7.9

STATISTICAL ANALYSIS

We used the EpiInfo statistical software to analyse results.10 Adjusted effects were explored by using unconditional logistic regressiotechniques with the EGRET software package,11 exploring each potential confounder individually and in combination. Categorical data were analysed with contingency tables, hypothesis testing being based on the χ² test for linear trend for social classes I through to V. Results are expressed in terms of prevalence with 95% confidence intervals.

OTHER CONDITIONS

To explore whether medical officers had a general tendency to overestimate visible skin disease in social classes I and II we also examined two other common inflammatory skin diseases recorded in the study -psoriasis and acne--with respect to social class (table IV). Visible psoriasis was recorded only at the ages of 11 and 16 and acne only at the age of 16. Prevalences for these two diseases showed no evidence of a strong social class gradient.

Prevalences of reported hay fever were also higher in social clases I and II, and the difference in prevalence between social classes increased from the age of 7 to 16 (table V). Prevalence of reported asthma or wheezy bronchitis, or both, in the past year did not show such trends.

Discussion

Other studies that have considered the possible relation between social class and eczema have given conflicting results.*RF 12-16* Our results suggest that the increased prevalence of reported eczema in advantaged socioeconomic groups is genuine. It is consistent at each stage of the follow up, regardless of how eczema is defined, and is also seen with housing tenure, another measure of socioeconomic advantage. The trend in social class for examined eczema was virtually unchanged after adjustment for potential confounders, and the proportion of reported cases validated by medical officer's examination increased rather than decreased in higher socioeconomic groups. Similar trends were not observed for psoriasis and acne.

Hay fever, but not asthma or wheezy bronchitis, showed the same social class gradient as eczema. Eczema and hay fever have also been shown to have similar associations with household size17 and region of residence,18 whereas asthma or wheezy bronchitis showed a different epidemiological pattern in this cohort.19 A genuine social class gradient for allergic diseases such as eczema is supported by the findings of a similar socioeconomic gradient for more objective measures of allergic disease such as positive results in skin prick tests.*RF 20-23*

One of the strengths of this study is its low potential for observer bias because medical officers were unaware of the hypotheses, which were suggested many years later, and information on social class was collected independently by an interviewer. A possible limitation is the reliance on medical officers' diagnoses of eczema. At the time the study was carried out eczema was used synonymously with atopic eczema for children in Britain. The prevalence of examined eczema is similar to that in other studies conducted at that time in developed countries,24 25 and the difference in prevalence between reported and examined eczema is entirely compatible with the twofold difference between the point and one year period prevalences for eczema found in other studies.26 27 Inclusion of cases of scabies and nickel dermatitis due to earrings would be likely to reduce rather than exaggerate social class trends shown in this study.28 29

Reporting bias could still have occurred if articulate upper middle class children were more likely to tell medical officers that they had eczema or if medical officers examined well turned out children more thoroughly. This seems unlikely as children were undressed at the time, and the skin examination was only a small part of a more detailed physical assessment. The lack of a social class trend for acne or psoriasis or for cases of examined eczema not validated by parental report lends weight to this argument. Social class differences of eczema may reflect factors that determine chronicity rather than incidence of disease. If this was the case examined eczema at the age of 7 should show a much stronger social class trend than reported eczema from birth to 7. This was not the case.

EXPLANATION OF THE TREND

There are many possible reasons for the social class trend for examined eczema shown in this study. Correlates of educational status, such as positive health related behaviour--for example, increased uptake of immunisation or differing rates of exposure to topical corticosteroids-- could be risk factors for eczema.2 Other factors such as differences in the use of carpets and heating (which could influence house dust mite populations),30 overuse of showers or soaps, decreased exposure to ultraviolet light, increased close contact with pets, and prenatal exposures correlated with higher social class such as higher maternal age and maternal diet also need to be considered.2 31

Our findings relate to British children in the 1960s and 1970s, and social class differences may have altered since. In developing countries a social class gradient in the opposite direction may be seen for eczema because of increased secondary infections, increased exposure to primary irritants through child labour, and reduced access and provision of medical care in less privileged groups.32

Atopic eczema causes much suffering and has a lifetime prevalence of around 12% at the age of 5 in the United Kingdom.1 The twofold variation in prevalence of eczema between the highest and lowest social classes represents a considerable burden of potentially preventable disease. Since environmental determinants of eczema are largely unknown, exploration of correlates with social class is a useful starting point. At the least, social class should be considered as a potential confounder for comparative studies of eczema prevalence.

We thank the Economic and Social Research Council Data Archive and the National Child Development Study User Support Group for making the data available for study and all those involved in the original study for recording information on skin disease. We also thank Barbara Butland for help with data processing. HCW is supported by the Wellcome Trust.