ABOVE: © ISTOCK.COM, HANNAHMARIAH

Past studies have suggested that living with pets during the first year of life lowers the risk that a child will develop allergies. A paper published in PLOS One today (December 19) now finds that this effect is dose-dependent—that is, the more pets in a baby’s house, the lower the risk that the child will go on to develop allergies years later.

“This is the hygiene hypothesis at work,” coauthor Bill Hesselmar, an associate professor at the University of Gothenburg in Sweden, tells The New York Times, referring to the longstanding idea that a lack of exposure to infectious diseases, microbes, or parasites in developed countries has led to climbing rates of allergies and other autoimmune conditions.

Hesselmar and his coauthors analyzed data from two previous Swedish studies, one that distributed a questionnaire to 7- and 8-year-olds, and another that followed children from [yes?] birth and then clinically tested them for allergies at age 8 or 9. The risk of allergies among the children decreased steadily with the number of pets they’d lived with as infants. Those with four pets had half the risk of the children who’d had none. “What’s fascinating to me [about the new Swedish study] is the more pets you have, the more protection you have,” Mimi Tang, an immunologist at the Murdoch Children’s Research Institute in Melbourne who was not involved in the research, tells the ABC.