Dogs make humans happy, and they also make kids healthier, finds a new study. University of Alberta researchers set out to find out why growing up with a dog is linked to lower rates of allergies. To do so, study leader and pediatric epidemiologist Anita Kozyrskyj examined baby poop. She found a higher diversity of microbes in the fecal matter of babies who lived in households with dogs. Exposure to more micorobes helps kids develop stronger immune systems. The same isn't true for adults, though owning a dog as a grown-up has been linked with lower levels of the type of inflammation related to diabetes, cancer, and cardiovascular disease, among other things.