It usually feels like we live in a toxic world here in Beijing, bombarded daily from the air and what we eat and drink. But what about the other extreme of being too clean? In our zeal to protect our families from toxins and germs, could we be harming as much as helping? This is more than an academic issue, as scientists are starting to realize that not all germs are created equal. In other words, there are good germs and bad germs. There is mounting evidence that an infant needs certain exposures to some germs in the first few months of life, otherwise they potentially could develop some immune-system diseases such as hay fever, eczema and allergic reactions — even obesity as an adult. This is called the “hygiene hypothesis”.

For example, a fascinating study published this summer followed 400 families and demonstrated that newborns who had a dog in the house had more than 30% reduction in the common cold, ear infections and antibiotic use during their first year of life. The researchers hypothesize that early exposure to a dog’s multiple germs carried from the outside are beneficial boosters for a small baby’s growing immune system. Does this mean you should run out and buy a pet? Of course not — many kids are allergic to pet dander, especially. But this is not the first study to find such a connection, and it brings up interesting topics: would that same allergic child be less allergic if they were exposed to more germs in the first few months of life?

As another example, there is mounting evidence that babies born by caesarean-section have a higher risk of childhood asthma and hayfever, and a new study published this summer showed a doubled risk of obesity in toddlers who were born by c-section. The possible reason again fits with this concept of early exposure to germs: a baby delivered by c-section isn’t picking up mom’s vaginal bacteria and thus may not be triggering an important immune system response. Also, perhaps those bacteria are an essential “starter colony” for baby’s brand new stomach and intestines, and these good bacteria are key for keeping a child’s weight down.

This brings up an exciting area of research: probiotics. We all know about “anti-biotics” which kill the “bad” bacteria, but our bodies are filled with trillions of good bacteria which actually are essential to our daily lives. For example, everyone’s digestive tracts are mostly made of certain bacteria which are essential for breaking down our foods and having healthy bowel movements. Antibiotics, especially the strong ones, often wipe out these healthy bacteria — which is why many people develop diarrhea after antibiotics (many women also develop vaginal yeast infections).

The good news is that mounting evidence shows that taking probiotic supplements while taking antibiotics can greatly reduce this common side effect of antibiotic-related diarrhea. A Cochrane Library meta-analysis published last year showed an impressive 48% decrease in diarrhea when taking probiotics. There are many types of probiotics, but this study suggested that a high dose (over 5 million colony units a day) especially with Lactobacillus rhamnosus or Saccharomyces boulardii was most effective. I think this is was a very impressive study which certainly has led me to encourage more patients of all ages to take probiotics while on antibiotics.

Probiotics are also essential to help recover from any type of infectious diarrhea, as another Cochrane review from 2010 showed a quicker recovery when taking probiotic supplements. It’s becoming quite important to always have some probiotics as a staple item in your medicine cabinet!

(This article was originally printed in Beijing Kids magazine, where I am a contributing editor. You can click here to read the rest of my BeijingKids “The Doc Is In” columns.)