Women with several kids have less allergies

The more children a woman has, the less likely she is to suffer from allergic rhinitis or allergic conjunctivitis. A small family size has previously been reported as a risk factor for allergies in children, giving rise to the hygiene hypothesis that suggests a reduction in infections in childhood leads to increasing allergic sensitisation. To look into the relationship between family size and mothers' allergies, researchers in Rome surveyed 1755 non-smoking women ages 35 to 74 living in four areas of northern central Italy. They reviewed self-reports of allergy symptoms and medical records. The team found that the rates of allergic rhinitis fell from 30 percent among women with no children or one child, to 16 percent among those with four or more children. Results were similar for allergic conjunctivitis, declining from 36 percent to 17 percent. The researchers suggest several theories that could explain their findings. For example, a woman's immune response could be related to fertility, or pregnancy may prevent allergies by altering the balance of inflammatory and anti-inflammatory factors, or perhaps through changes in maternal nutrition with increasing number of children. Another possibility is that the hygiene hypothesis may apply to mothers as well as children.