Dogs can develop natural odors from secretion from anal glands, ear wax buildup, or even bad breath.
Normal Causes
Allergic reactions to food or environment can cause extra yeast and bacteria growth on skin, resulting in musty smells.
Allergies
Bacterial or fungal skin infections like yeast can lead to foul odors emanating from hot spots or armpit area.
Skin Infections
Periodontal disease and tooth abscesses in dogs can cause terrible mouth odors.
Dental Disease
Inflammation and infection deep in dog's ear canals can create a stench and require medication.
Ear Infections
Flatulence from dogs eating inappropriate human foods or intolerance to some dog foods can be quite smelly!
Gas
Lack of regular grooming to express anal glands, clean ears, trim hair, and brush teeth can worsen smells.
Grooming