July 9, 2012 -- Babies in homes with dogs have fewer colds, fewer ear infections, and need fewer antibiotics in their first year of life than babies raised in pet-free homes, Finnish researchers find.
Homes with cats are healthier for babies, too, but not to the same extent as those with dogs, note researchers Eija Bergroth, MD, of Finland's Kuopio University Hospital, and colleagues.
"The strongest effect was seen with dog contacts. We do not know why it was stronger than with cat contacts," Bergroth tells WebMD. "It might have something to do with dirt brought inside by the dogs, especially since the strongest protective effect was seen with children living in houses where dogs spent a lot of time outside."
To take a closer look at the situation, Bergroth's team followed 397 Finnish children from their third trimester of pregnancy through their first 12 months of life. Parents filled out weekly diaries with detailed information on their child's health and on their child's contact with dogs and cats.
They found that compared to kids in pet-free homes, kids in homes with dogs:
Why Might Dogs Make a Difference?
It's not clear why living with a dog makes such a difference.
"It might have something to do with the dog itself as an animal," Bergroth suggests. "The living environment can also affect this. These children lived in rural or suburban areas, so inner-city kids -- and dogs -- might get different results."
A time-honored theory, the hygiene hypothesis, suggests that children's immune systems mature best when infants are exposed to germs in just the right amount. Too many germs are unhealthy, but so is a sterile, germ-free home.
That theory is now giving way to the "microbiome hypothesis," says Karen DeMuth, MD, MPH, assistant professor of pediatrics at Atlanta's Emory University.
"The microbiome hypothesis is that early-life exposure to wide varieties of microbes lets them mix with the microbes in the gut and helps them keep the immune system from reacting against itself and causing autoimmune disease, or from reacting against stuff you should ignore and causing allergy," she says.
The hygiene hypothesis has indeed changed, says Anna Fishbein, MD, an allergy and immunology fellow at Northwestern University and now an assistant professor at the University of Maryland.
"It's become more complicated. It's no longer just getting exposed to the right number of microbes, but to good bacteria and viruses that alter the microbes in our intestines and protect us against both allergies and infections," Fishbein tells WebMD.
Dogs Not Good for All Kids
But one child's good microbes are another child's bad microbes, DeMuth warns.
"There is also an interaction between these microbes and an individual child's genetics," she says. "Certain people who have a dog in the house are protected against infections and allergies, but some are not. This is not a one-size-fits-all kind of thing."
Worst of all, DeMuth says, is for the family of a sickly or asthmatic child to bring a dog into a pet-free home in the hope that it might help.
"The absolute wrong thing is to put a dog in the house for kids with asthma," she says. "Yes, having a dog in the house early can protect against wheezing or respiratory infections. But this exposure has to happen very early in life."
What about parents who are themselves allergic to dogs or cats? Should they bring a pet into the home for the sake of their soon-to-be-born child?
"This is always a hard question," Bergroth says. "But it is important for the child that its parents can live happily in the home without symptoms."
The Bergroth study appears in the August 2012 issue of Pediatrics.