If your morning breath is consistently ripe—even if you brush your teeth regularly—you could be dealing with undiagnosed sleep apnea, a disorder that causes your breathing to sporadically stop and start while you sleep.
Sleep apnea can lead to excessive snoring, causing you to breathe through your mouth throughout the night. This can make your mouth very dry, which is a common cause of bad breath, says Raj Dasgupta, M.D., assistant professor of clinical medicine at the University of Southern California.
This allows bacteria to breed more readily—and when certain kinds multiply, they produce a sulfurous gas that can give your breath a rotten egg smell.
If you’ve ruled out other causes of bad breath, but still wake up with a smelly mouth and you suffer from daytime sleepiness and snoring, schedule an appointment with your doctor. It’s vital sleep apnea gets diagnosed quickly: The sleeping condition has been strongly associated with diabetes, high blood pressure, and heart disease, so treating it sooner than later can spare you of its long-term health effects, Dr. Dasgupta says.