A group of scientists from Yale University say designing a home that lets "good bacteria" in could help to reduce allergies and asthma.

A squeaky clean home, free of bacteria and fungi, may not be as healthy as you think, say US experts.

Scientists from Yale University say inviting "good bacteria", into your home can help to prevent allergies and possibly asthma.

In a paper published in the journal Trends in Microbiology, they make a case for building homes that let the right microbe in, rather than trying to keep all bugs out.

"It's a common misconception that all microbes found in one's home are hazardous to your health," says Yale Professor Jordan Peccia.

They point to past studies showing that kids who grew up on farms, where they were regularly exposed to bacteria, were less likely to develop allergies.

One particular study found children from a Bavarian family, a population known for their farming lifestyle, had less than half the levels of asthma compared to a suburban European family - 5.2 per cent compared to 19.1 per cent.

This was likely because the good bacteria sends signals to white blood cells, known as T cells, to prevent an unnecessary immune response.

When someone has an allergic reaction to a substance, such as dust or pollen, their immune system overreacts by producing antibodies that attack the allergen, causing them to wheeze, itch or get a runny nose.

As the scientists learn more about which microbes are beneficial to human health, they suggest building design could potentially be used to change the exposure to these good bugs through ventilation, building materials and layout.

"As more and more beneficial microbes are identified, we - architects, engineers, and the general public - need to think about how we can facilitate our exposure to them," Prof Peccia said.

It's acknowledged the research is still in its infancy, and that one obvious hurdle to improving a home's ventilation is poor outside air quality in many cities.

However, one way to "train" the immune system is through exposure to animals, especially cats and dogs, says Prof Peccia.

"Not everyone should run out and get a dog, of course," he says, "but we can work to develop new, quantitative approaches for solving these problems - something better than our portable air filters and inhalers."