A new study by researchers in Sweden found that children who are exposed to household pets early in life are less likely to develop conditions like asthma, eczema, and hay fever—and the more pets, the better.

For the study, the researchers interviewed and sought information on pet ownership from the parents of 249 children (who were 6 to 12 months old at the time). Those children also were given clinical evaluations at regular intervals along the way, up until the age of 8 or 9. The parents of another 1,029 children (ages 7 and 8) were given questionnaires about pet ownership and the incidence of asthma, eczema, and hay fever.

In both groups, allergy reports declined steadily as the number of pets rose.

For instance, in the larger group, a hefty 49% of kids with no pets during their first year of life suffered from allergies, compared to zero allergies in kids who lived with five or more pets. In the middle, 43% of kids with one pet had allergies and 24% of children who had three pets as a baby had allergies. The smaller group showed a similar pattern.

The authors note that while most allergy research focuses on identifying risk factors for allergy development, finding lifestyle factors that could prevent allergies has become equally important.

And while other studies have shown that early childhood exposure to pets may reduce the risk of developing allergies later in life, the new study’s corresponding author Bill Hesselmar, MD, PhD, pediatrician at the University of Gothenburg in Gothenburg, Sweden, says this study is the first of its kind to show pet ownership dose-dependency on allergy risk.

The researchers controlled for many factors—such as the influence of parental allergic disease on the families’ choice to have pets—but the link between pet ownership and decreasing risk for allergy persisted.

Hesselmar suggested that the study is a good example of the hygiene hypothesis at work. The hypothesis states that a lack of early childhood exposure to parasites, infectious agents, and symbiotic micro-organisms increases susceptibility to allergic diseases by suppressing the natural development of the immune system.

In this case, having pets early in life may train the immune system through exposure to more microbes and pieces of bacteria.

The authors suggest that having pets in the house may create a “mini-farm” effect, a reference to the fact that approximately 30% of children in the industrialized world have allergies—except those who live on farms, where the incidence of allergies is much less than in children who don’t live on a farm in the same area.

Because exposure to microbes and bacteria that thrive on farms—and more significantly, on farm animals—protects children from allergies and asthma.

But if you want to protect your children from allergies, it may be more practical to adopt another cat or two than a couple of companion cows.

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