The smell of metal on the breath can be a symptom of gum disease, notes WebMD. Foul breath in general may be caused by numerous other throat or mouth conditions, such as having an infection, cavities or cancer.
Bad breath that doesn't result from some kind of disease or other bodily condition often results from low levels of saliva production, which allows bacteria to flourish, according to WebMD. Smoking and eating certain pungent foods are also known culprits of unpleasant breath. Saliva is largely stagnant when people are asleep, which sets the course for bad breath when upon awakening. Saliva may also be low from dehydration or alcohol consumption.