All people can develop body odor when certain bacteria or fungi colonize on their skin. Normal sweat doesn’t smell when it first reaches your skin. The odor usually comes only after certain microbes on the skin’s surface break down the fat in sweat to form chemicals that smell. Most sweat glands produce sweat that contains no fat, but the sweat glands around the breasts, genitals and armpits produce sweat that contains fat.

Most people will not develop body odor, even when they rarely take a shower or bath. You can usually help to control body odor by bathing frequently, and perhaps applying an antiperspirant or deodorant after you bathe. Most antiperspirants contain aluminum that reduces sweating. Deodorants repel some odor-causing bacteria. Your doctor can prescribe a stronger prescription-strength antiperspirant or deodorant if you feel that you need one.

Other anti-odor measures include
• Wearing clothing made from breathable cotton, silk, or wool
• Wearing moisture-wicking fabrics such as polyester or nylon when you exercise
• Washing exercise clothes after each wearing
• Changing underwear and socks daily, because underclothes retain skin debris that bacteria can break down to cause odors
• Using powder under the armpits and groin to keep the skin dry, which reduces bacterial growth
• Shaving your armpit hair

If you have body odor problems that are not solved with these measures, check with your doctor to look for conditions that increase sweat and odors. You may benefit from botulinum toxin injections or prescription medications that reduce sweating. If you do all of these things and still have an odor, something may be wrong.

Causes of Unusual Body Odors
The most common cause of unusual body odor is a skin infection with odor-producing bacteria or fungi. However, body odor can also be a sign of disease (Int J Mol Sci, 2020 Apr; 21(8): 2886). Your doctor will check you for a sinus infection, acid backing up from your stomach, or dental disease. Next you need tests for diabetes and liver or kidney damage. There are several conditions that cause the accumulation of certain chemicals that produce odors.

• An ammonia odor can be caused by infection with Helicobacter pylori, the bacteria that causes stomach ulcers. Your doctor can do a very dependable stool DNA test for helicobacter. If it is positive, you can be cured with antibiotics.
• An ammonia smell can also come from liver or kidney disease, as well as from dental plaques or gut infections.
• A fish odor can be caused by taking choline supplements or by a hereditary condition called trimethylaminuria that requires restricting high-choline food sources such as animal products, dairy, eggs, meat and fish (International J of Dermatology, Feb 1995;34(2):92-3). A fishy smell can also be caused by a vaginal infection caused by a bacteria called Gardnerella, or by pyridine from a dental infection. People who have a damaged liver can also develop a fish odor. Liver damage can destroy the chemical that breaks down choline.
• Breath smelling like fruit can come from ketones produced by uncontrolled diabetes. Ketones are also produced by fasting, a high-fat diet or a ketogenic diet.
• Rotten egg odors can come from urinary infections.
• A cheesy “sweaty feet” smell can come from short chain fatty acids that accumulate during liver or kidney failure.
• A rancid butter odor or boiled cabbage odor can come from an inherited metabolic disease.

My Recommendations
Most people will not suffer from body odor even if they bathe only once a month or work under filthy conditions. Most of the time, body odor is caused by bacteria on the skin converting components of sweat into chemicals that smell. If you can’t control body odor with some of the steps listed above, check with your doctor to see if you have a medical cause that may need particular attention and treatment.