The prevalence of childhood allergies, such as hayfever, have increased over the past decade in many countries of the world, especially among younger age groups, reveals an article in this week's issue of The Lancet.
In 1991 researchers carried out the International Study of Asthma and Allergies in Childhood (ISAAC) to assess the worldwide prevalence of asthma, hayfever, and eczema*. Between 2002 and 2003, Innes Asher (University of Auckland, New Zealand) and colleagues repeated ISAAC to examine any changes in prevalence. The investigators surveyed the parents of over 193 400 children aged 6-7 years from 37 countries on the presence of symptoms of asthma and allergies, such as wheezing, in their child. They also asked around 304 680 children, aged 13-14 years from 56 countries, the same questions. Developing countries such as South Africa, Brazil, and Iran and developed countries such as Canada, New Zealand, Sweden, and the UK contributed to the study.
The investigators found that increases in prevalence were more common than decreases and occurred more commonly in the younger age-group. The increases were greatest for eczema in the younger age-group, and for hayfever in both age-groups. However, in the older age group where prevalence of asthma had been previously been high, symptoms of the condition more commonly decreased. The only regions where increases in prevalence of all three disorders occurred more often in both age-groups than decreases were Asia-Pacific and India.