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Key factors that affect a child's risk of developing allergies by age two include race, a mother's exposure to pets during pregnancy and the method of delivery, a new study suggests.
Researchers at Henry Ford Hospital in Detroit followed 1,187 newborns and measured levels of the antibody immunoglobulin E (IgE) in blood samples collected from the babies at birth, six months, one year and two years.
IgE is associated with the development of allergies and asthma; higher levels indicate increased risk.
The study found that IgE levels during infancy were 28% lower in children whose mothers were exposed to indoor pets during pregnancy (indoor prenatal pet exposure) compared to babies from pet-free homes.
IgE levels were 16% lower in infants who had indoor prenatal pet exposure and were born vaginally compared to infants who had indoor prenatal pet exposure and were delivered by caesarean section.
The hygiene hypothesis
IgE levels were 33% lower in infants of European, Asian or Middle Eastern descent who had indoor prenatal pet exposure, compared to 10% lower in black infants with indoor prenatal pet exposure. The study was published online in the Journal of Allergy and Clinical Immunology.
"We believe having a broad, diverse exposure to a wide array of microbacteria at home and during the birthing process influences the development of a child's immune system," senior study author Christine Cole Johnson, chair of the Department of Public Health Sciences, said.
The finding supports what's known as the hygiene hypothesis, a theory that early childhood exposure to infectious agents affects immune system development and the risk of allergies and asthma, she added.
More information
The Nemours Foundation has more about allergies in children.
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