Milk causes bad breath in several ways
Drinking milk is good for bone and skin health, but it rarely does breath any good. A glass of milk can cause a very distinct form of halitosis, often called "milk breath." However, beyond this common ailment, dairy products may cause bad breath through the less common route of lactose intolerance.
In a typical mouth, the tongue, teeth and palate are coated with millions of bacteria. After a drink of milk, these microbes go to work digesting the leftover lactose, lipids and proteins that coat the mouth.
Over time, this digestive process results in an excess of hydrogen sulfide in the mouth, which can cause a sour smell on the breath. Babies often have very pronounced milk breath, for obvious reasons.
However, lactose intolerance may also cause halitosis. Experts recently wrote in the Chicago Tribune that while there are few medical studies linking lactose intolerance to bad breath, it is still a possibility.
In order to avoid the smell of bad breath, it may help to rinse with a specialty breath freshener after consuming dairy products.