There is a direct link between levels of hygiene in the home and the occurrence of wheeze and eczema in children under 3½ years of age, according to research published today.
As part of a long-term study of parents' and children's health, 11,000 children in the Bristol area are being assessed for various health outcomes. A simple hygiene score was devised based on the frequency of hand-washing, bathing and showering.
Parents were also surveyed about the children's respiratory and eczema symptoms at 6 months and again between 30 and 42 months of age.
The results, published in the current edition of Archives of Disease in Children, showed that for every unit increase in the hygiene score, the likelihood of a child wheezing between the ages of 30 and 42 months increased by 4 per cent.
In younger children, the level of wheezing was partially explained by the frequency of use of chemical products to clean the home; certain strong household chemical are themselves known to irritate the airways.
However, the link between eczema and high hygiene scores was even stronger, according to Dr Andrea Sherriff, of the department of child health at the University of Bristol. This was especially the case in children whose eczema was severe.
According to the authors, today's research adds further weight to the "hygiene hypothesis" in which improvements in hygiene are thought to be responsible for the rise in prevalence of allergic disorders.
It has previously been shown that exposure to dirt and infection early in childhood confers protection against diseases such as asthma and eczema. Specific protective factors include having an older sibling, attendance at day care, living on a livestock farm and owning a furry pet.
Commenting on the results, Dr Denis Gill, professor of paediatrics at the Royal College of Surgeons in Ireland and Temple Street Children's Hospital, said they provided further evidence that viruses and other infectious agents had some part to play in protecting children from diseases linked to the immune system.
"It seems as if infection in early life is valuable in the sense of priming the immune system," he added.