Dog saliva contains a natural disinfectant that kills bacteria better than most soaps. This means that a dogs' mouths are often cleaner than human hands, even if they sometimes eat unsavory leftovers, according to the Geophysical Institute. In spite of this, a dog's breath can often be overwhelming, and there are a number of things you can do to improve it.
The simplest way to disinfect your dog's mouth is by feeding him dental treats. You can find them at your local grocer or pet store, many in minty flavors.
If your dog continues to suffer from bad breath, he may have a rotten tooth or gum disease. Gently open his mouth and look for discolored teeth or reddened gums. Try beginning regular brushing yourself, and be sure to mention the issue to the veterinarian at your next appointment.
Another cause of bad breath is diet. Many dog foods are made from low-grade meat byproducts that are unfit for human consumption. Likewise, they have ill-effects on canines, too, the most obvious example of which is bad breath. Switch him to a high-quality diet and his breath should clear up after about a next week.