Milk can cause bad breath in two distinct ways
Though the term may sound exotic or made up, "milk breath" is a very real condition, one that your nose usually recognizes instantly. It is caused by dairy products, and can come about in two separate ways.
The first is the simplest. Drinking milk gives oral bacteria something to digest. Once these microbes have processed the milk residue on your tongue, they emit volatile sulfur compounds, which are molecules that smell quite bad.
If you've ever had a tall glass of milk and neglected to rinse with a specialty breath freshening product afterwards, you may have become intimately familiar with this form of bad breath, and if you didn't, your friends almost certainly did.
The other, less common form of milk breath is caused by an inherited inability to digest the sugars in dairy products.
While it is relatively rare, halitosis can certainly be caused - or more commonly, exacerbated - by lactose intolerance. This digestive disorder can result in a number of unpleasant symptoms, including gas, bloating and halitosis, according to the National Institutes of Health.
Avoiding dairy products is one way to avoid such oral odor, and using an oral care probiotic every day can also help gradually reduce your bad breath over an extended period of time.