Having siblings, pets and living on a farm reduces the risk of allergic illnesses in babies but having early infections increases it, say Danish researchers.
Sterile, modern environments have been blamed for the increase in asthma, dermatitis and other allergic diseases over the past century because the immune systems of babies
are not exposed to many microbes.
Scientists have also thought that early infections would protect against allergies but Christine Stabell Benn, of the Danish Epidemiological Science Centre in Copenhagen, found they increased the risk of developing allergies.
"We found that having older siblings protects against allergic diseases but it is not by means of transferring infectious diseases because those diseases are actually associated with an increased risk of disease in the child," Dr Stabell Benn said.
"With each infection the risk [of an allergic illness] increases."
The human immune system developed to deal with many different microbes. Scientists believe that when it doesn't encounter them early in life, it overreacts later and allergic diseases develop.
Living on a farm, attending day care and having older siblings or pets increase a baby's exposure to microbes.
Dr Stabell Benn and her team interviewed 24,000 women during pregnancy and when their children were six and 18 months old. Their findings are reported online by the British Medical Journal.
About 10 per cent of the children suffered from dermatitis at 18 months. The researchers found that the risk of allergic illness increased with each infectious disease the child suffered before 6 months, but it decreased if the child had three or more siblings, attended day care or lived on a farm or with pets.
- REUTERS
Herald Feature: Health
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