Ask the Doctors: Is there anything to ‘hygiene hypothesis’ tying cleanliness to immune system?

Dear Doctors: Our sister is a messy housekeeper. She calls it the “hygiene hypothesis” and says it’s why her kids don’t have asthma or allergies and don’t catch colds often. Does avoiding antibacterial products and letting the dogs on the couch really keep her kids healthy?

Answer: An emerging area of study examines our home environments and their potential effects on health and the immune system. These are the basic components of the “hygiene hypothesis.”

Your sister is referring to questions about our modern-day standards of cleanliness — howh the spaces where we live and work affect our health and immune systems.

The hygiene hypothesis dates to the late 1980s. It focused on asthma, considered the most common chronic disease in the developed world. The thinking was that, when infants are raised in the ultra-clean environments of the modern home, their developing immune systems fail to encounter the wide variety of microbes needed to educate their immune systems, resulting in immune responses that go awry, leading to childhood allergies and diseases, including asthma.

Newer sister theories suggest that being raised in germ-free environments might lead a child’s developing immune system to become trigger-happy. An array of “friendly” bacteria, fungi and viruses plays a part in keeping our bodies functioning properly. The idea is that reduced exposure to these can lead to an overreaction by the immune system when it encounters unfamiliar microbes, including those that don’t pose a threat.

These are all just theories, subjects of robust debate, and no specific mechanisms for or against these hypotheses have been identified. Still, it won’t be a surprise if the relationship turns out to be even closer and more complex than we originally suspected.

Regarding antibacterial household products, we urge caution. They can be effective at eliminating certain harmful germs, but hey wipe out vast swaths of beneficial microbes and have the potential to play a role in antibiotic resistance.

It’s not that adherents to the offshoots of the hygiene hypothesis are urging us to live in dirty homes. It’s about striking a reasonable balance between cleanliness and zero tolerance.

Dr. Eve Glazier and Dr. Elizabeth Ko are internists who teach at UCLA Health.