Dog aren't just cool. They can also have health benefits.

A recent study shows that dogs can help strengthen immune systems of children against allergies and asthma if they are exposed to them, as well as barnyard animals, within the first three months of life.

The study, published in the New England Journal of Medicine, was conducted on children on farms. It found that those who lived in close proximity of animals, especially youngsters in the Amish community, were less likely to have asthma than those who grew up on industrialised farms away from animals.

It all comes down to a more diverse biome - a naturally occurring community of flora and fauna - Dr Jack Gilbert, Director of the Microbiome Centre at the University of Chicago, told The New York Times.

Dogs especially can add 'good' bacteria and microbes inside homes because they play outdoors more frequently than other pets.

Another study concluded that "dog ownership raised the levels of 56 different classes of bacterial species in the indoor environment, while naturally more fastidious cats boosted only 24 categories," the newspaper reported.

Not all animal bacteria is good, of course, and that from cats, turtles, and frogs is less helpful, according to researchers and veterinarians.

Pet owners will be the first to name the numerous pieces of animal faeces, sidewalk substances, and types of dirt pets can track into homes. Combined with the millions of bacteria that survive in house dust pets can sometimes carry salmonella and other diseases to humans, but general medical advice suggests its avoidable with simple hand washing.

Researches are also doing "a lot of work on finding out exactly which organisms make children healthier, and isolating from the animals on the farms and producing defined probiotics to elicit the same benefit", Mr Gilbert told The Independent.

He also said that those with a certain type of already-compromised immune system, specifically people with severe sepsis, "can be treated with microbial exposure".

However, "that's a big question" still being examined.

Netzin Steklis, a biologist at the University of Arizona, said: “Dogs have been with humans for 40,000 years...but we are only now looking to find out how living with them impacts our health."