Ask A Scientist

What causes body odor?

Asked by: Emily Puthawala
School: St. James Middle School
Grade: 8
Teacher: Mrs. Walter
Hobbies/Interests: Horseback riding, reading and drawing

Answer from Guruprasad Madhavan

PhD Candidate in Biomedical Engineering and Graduate Research Assistant, Clinical Science and Engine

Research area: Medical Devices, Integrative Physiology, Circulation, Chronic Diseases, and Complex Systems
Interests/hobbies: Music, Movies, Reading, Traveling, and Searching for Black Swans
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Body odor (bromhidrosis, or more simply—B.O.) is something we all sweat about. Be it a gym, sports locker room, crowded place, or class room, the sometimes shockingly aromatic smell of the human body can draw unwelcome attention. Body odor is related to perspiration. When we perspire, water molecules (sweat) evaporate from our skin—that is, they leap from the skin into the air, but only the fastest moving molecules have enough energy to make the leap.  Once they do make the leap, they carry that energy away with them. When the body loses the water molecule—and its energy—it cools down. In fact, perspiration evolved as an efficient mechanism for us to cool ourselves when it is hot outside. Sweating is so powerful that two drops of sweat can cool up to a quart of blood by one degree Fahrenheit. So how does body odor enter the picture? It turns out that the sweat itself isn’t the culprit. It is the unholy union of sweat with bacteria on the skin surface that can sometimes result in a displeasing smell. Our body produces two different types of sweat. One of them is watery and salty, and is produced by the eccrine sweat glands. We each have up to five million eccrine glands scattered all over our bodies, which have happily sweated away since birth. Eccrine sweat is released whenever the body temperature goes up. The sweat evaporates from the skin surface and cools our body to a temperature we are comfortable at.  The second type of sweat is produced by the apocrine sweat glands. This type of sweat is oily and thick, and has little to do with temperature regulation. Apocrine sweat comes from a few thousand glands located in areas such as the armpits, chest, and groin. These glands do not become active until puberty, which may be one reason why babies smell so sweet. Bacteria on the skin surface love to interact with this thick sweat. Depending on the concentration of apocrine sweat, the odor can range from fragrant to offensive. The type and intensity of the smell from apocrine sweat and its associated bacteria is determined by many factors. Various food substances such as garlic, onion, spicy red hot peppers, and red meat can have an effect on our sweat, as can emotions such as anger, anxiety, stress, and pain, and sicknesses such as a cold or the flu. Lifestyle factors such as smoking and drinking can also influence body odor. Body odor is even believed to have a genetic basis—those of European heritage, for example, are more prone to body odor. It is tough trying to imagine what life must have been like in Europe during the era of Queen Elizabeth I in the mid-1500s, when personal hygiene was out of fashion. Some historians suggest that the fall of the Roman Empire brought with it a sad decline in European bathing practices that lasted for several centuries adding to the great plagues that swept the land. Many nutritionists advise that we can control our body odor by drinking plenty of water and perhaps most importantly, by increasing our intake of leafy vegetables. Since leaves are rich in chlorophyll and phytonutrients, they have the ability to cleanse our system internally, which results in less oily sweat on the skin surface. Periodically washing and trimming hair, which is a big bacteria trap, can also help to control body odor. Deodorants and anti-perspirants are synthetic products that can reduce body odor. Many people think a deodorant is the same as an anti-perspirant, but they actually have quite different uses. Deodorants are perfumed chemicals that help reduce apocrine smell. Anti-perspirants, on the other hand, are aluminum-based compounds designed to plug sweat ducts and reduce the sweating rate. Deodorants and anti-perspirants are so popular for odor control that last year alone, Americans spent nearly two billion dollars on these products. Many natural remedies can also be used for odor control. The ancient Mesopotamians and Egyptians used distilled flower oils and fragrant spices to fight body odor, while people from India were known to use sandal wood oil, turmeric paste, and incense-based aromatics.  We cannot conclude the topic of body odor without discussing the feet. On a warm summer day, each of our feet, when covered with sock and shoe, is capable of producing more than a quart of sweat. Inadequate ventilation leads to bacteria sticking on to our sweat—and our skin—for a long time. This intensifies the odor. Periodic ventilation, sweat-absorbing cotton socks or shoe inserts, or anti-bacterial sprays, can help fight malodorous feet. There are also extreme cases in perspiration. One case is where people constantly have sweaty palms or feet or face, regardless of their mood or weather. This condition of “over-sweating” is called hyperhidrosis, and may result from disorders of the immune or endocrine systems. On the other hand, little or no sweating can be lethal, because our body’s ability to regulate the temperature is severely challenged. This condition is called anhidrosis and is known to results from factors such as dehydration, sweat gland infections, or more serious neurological issues.

Last Updated: 3/1/17