The main cause of a smelly belly button is inflammation of the belly button, caused by bacterial infection. There will be oozing inside the belly button and there may be pus, so it causes the smell to be bad. There may also be eczema in the navel, caused by oozing from the surface. The main cause of eczema may be allergies, such as wearing chemical fiber clothing and cause. If there is eczema, it is advisable not to pick it with your hands. Because the liquid flowing around the navel will lead to the expansion of the eczema, you should change the cotton underwear and apply hormone or antihistamine medication on the surface to treat the symptoms. If the surface of the eczema is broken, red and swollen, and infection is suspected, you can also apply antibiotic ointment, such as oxyfloxacin ointment.