Sweating underarms will have a bad smell may be caused by physiological factors such as local cleaning is not in place, but also may be caused by hyperhidrosis, fox odor and other diseases. 1. Physiological factors: If you don’t clean the local area in time after sweating in the armpits, which leads to an increase in the number of bacteria in the armpits, you may have a bad odor in the armpits. 2. Hyperhidrosis: the etiology may be related to genetic, drug and other factors, emotional fluctuations, obesity may also induce the disease. Patients will have paroxysmal or persistent localized hyperhidrosis, which may be accompanied by the phenomenon of odor, most commonly found in the perineum, armpits and other parts of the body. 3. Fox odor: the etiology is not clear, may be related to genetic, environmental factors. The main manifestation is that the armpits emit a pungent odor, and at the same time there will be excessive sweating. Causes of underarm sweating will have a bad smell of more reasons, in the exclusion of physiological factors, it is recommended to go to the regular hospital for examination to clarify the cause of the disease.