Review
Recent perspectives on the global epidemiology of childhood eczema

https://doi.org/10.1016/j.aller.2011.02.004Get rights and content

Abstract

The International Study of Asthma and Allergies in Childhood (ISAAC) is the largest epidemiological study ever performed and the only truly global allergy study. This review summarises the childhood eczema-related findings from ISAAC and discusses how these fit into our current understanding of eczema aetiology, with particular emphasis on worldwide time trends in eczema prevalence, climatic and dietary risk factors, breastfeeding, the role of skin barrier impairment and allergic sensitisation.

Section snippets

Global prevalence surveys and time trends

Prior to the ISAAC Phase One survey, very little was known about the prevalence of childhood eczema outside of Northern Europe. Phase One collected data from 256,410 children aged 6–7 years in 90 centres and 458,623 participants between 13 and 14 years of age from 153 centres.5, 6 The validated ISAAC eczema questions, which were used in all study centres, are shown in Box 1. There were significant prevalence differences between paediatric populations for all eczema outcomes in both age groups.

Climate

One potential explanation for prevalence differences between populations is climate; an area that had previously received little attention with regard to eczema. Based on the Phase One data set, an ecological analysis was conducted using information on long-term climatic conditions in the different study areas from the World Weather Guide.8 Variables that were examined included latitude, altitude, average outdoor temperature and relative outdoor humidity. The results, which were adjusted for

Diet

Another potential explanation for prevalence differences between countries are dietary factors. Given how uncommon eczema and other allergies still are in most developing nations, an important question is whether consumption of a ‘western’ affluent diet (i.e. high intake of refined grains, cured and red meats, as well as saturated and unsaturated fatty acids) is associated with an increase in eczema risk. This was explored in another ecological analysis from ISAAC Phase One, looking at the

Breastfeeding and delayed weaning

Many advocate breastfeeding as a way of preventing allergies, including eczema. For instance, the World Health Organization (WHO) recommends that babies are exclusively breastfed for 6 months,29 and most European ministries of health advocate at least 4 months of exclusive breastfeeding to aid allergy prevention. It is therefore conceivable that differences in the length of breastfeeding and the age infants are weaned onto solids could explain part of the eczema prevalence differences between

Skin barrier dysfunction and allergic sensitisation

If it is true that the early introduction of potentially allergenic foods through the oral route induces immunological tolerance, then this raises the question as to whether penetration of food and aeroallergens allergens across the impaired barrier in inflamed eczematous skin can induce allergic sensitisation. This would also suggest that atopy is a secondary phenomenon in eczema, rather than being a primary event in eczema development.

ISAAC Phase Two data has shown that the odds of allergic

Where do we go from here?

ISAAC provides a unique cross-sectional data set to study potential risk factors for eczema development. Much of the collected ISAAC data remains to be explored, such as information on the management of allergic disease in different countries and risk factor analyses to explain urban versus rural prevalence and severity gradients between ISAAC centres in the same country. However, it is important to recognise the limitations of cross-sectional study designs, which cannot be compensated by size

Conflict of interest

None.

Funding

CF is funded by a Clinician Scientist Award from the UK National Institute for Health Research (NIHR). The views expressed in this publication are those of the author and not necessarily those of the UK National Health Service, the National Institute for Health Research or the UK Department of Health.

Acknowledgements

This article was originally published in German in “Allergologie” and has been reproduced in English with the kind permission of Dustri-Verlag Dr. Karl Feistle GmbH & Co KG, Munich, Germany. CF is a member of the ISAAC Steering Committee.

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