Your guests may bring home immunity-improving bacteria!

Washington: Like having guests over? They may come with a host of unexpected visitors - millions of bacteria cells that could improve your immunity, scientists say.

According to researchers, every guest entering our homes emit 38 million bacterial cells an hour. Even if a guest walked into the kitchen and held their breath, they still would slough off 10 million bacterial cells in just 60 minutes through skin shed, said Jack A Gilbert, associate professor at University of Chicago.

"Nearly all of the germs graciously donated by our friends and family are not disgusting. They are probably good for us in many different ways," said Gilbert. Gilbert said our over-sanitised environment may ultimately leave us weaker than our ancestors, who were agrarian and were constantly surrounded by a wide variety of plants and animals.

Their bodies adapted to such changes - and so our bodies expect to encounter them, too, he said. "Our ancestors experienced many different types of bacteria on a regular basis. When you live with such rich biodiversity, the body expects to see it and when it doesn't, it freaks out, which is why we are seeing an explosion in allergies, asthma and hay fever," said Gilbert.

Our constant hand washing - though it might prevent a nasty flu - might also keep us from developing immunities. "We have done a really good job at keeping the bad bugs at bay, but we've failed at keeping in those that we need because we live an indoor, sedentary lifestyle," Gilbert said.

Inviting friends and family to come around on a regular basis may help stimulate our immune systems, he said. Likewise, having very young children interact with a wide variety of animals is only beneficial to their health and greatly outweighs the slim chance of exposure to something harmful, he said.

In fact, Gilbert believes some of the social rituals we carry out today - hand shaking, hugging, kissing - may have evolved over millennia as a way to share, spread and develop immunities to bacteria. Kissing, for example, may promote healthy digestion, train the immune system and may even lead to better cognition, Gilbert said. Germs are so prevalent and impossible to eliminate, Gilbert said, there is no need to go overboard scrubbing the house after gatherings.