The Science of Body Odor - Effective Strategies Starting from the Fact That Sweat Itself Is Odorless
Sweat Is Odorless - Skin Bacteria Are the True Culprit
The phrase "smells like sweat" is used casually, but sweat itself has almost no odor. Sweat from eccrine glands is 99 percent water, with the remainder being salt and minerals. When smelled immediately after secretion, it is confirmed to be virtually odorless.
Body odor occurs because sweat and sebum are broken down by bacteria living on the skin surface. As resident bacteria metabolize proteins and lipids, volatile organic acids and sulfur compounds are produced. In other words, the essence of body odor management is not "stopping sweat" but "controlling bacterial growth and metabolism."
Two Types of Sweat Glands - Eccrine and Apocrine
Eccrine Glands: Temperature-Regulating Glands Distributed Throughout the Body
Approximately 2 to 5 million eccrine glands are distributed across the entire body, primarily secreting sweat for temperature regulation. The sweat produced is a watery solution composed mostly of water and sodium chloride. Eccrine sweat causes body odor only when it remains on the skin surface long enough for resident bacteria (particularly Corynebacterium and Staphylococcus species) to break it down. Foot odor and post-exercise sweat smell result from this mechanism.
Apocrine Glands: Odor-Producing Glands Concentrated in Armpits and Groin
Apocrine glands are concentrated in the armpits, groin, areolae, and external ear canals. They secrete a milky, viscous fluid rich in proteins, lipids, and ammonia. When this sweat is broken down by skin bacteria (particularly Corynebacterium), strongly odorous substances like 3-methyl-2-hexenoic acid (3M2H) are produced. The characteristic underarm odor (known as osmidrosis) originates from these apocrine glands.
Genetic Background of Underarm Odor
The number and activity of apocrine glands are genetically determined. Variants in the ABCC11 gene are associated with underarm odor tendency, and this gene also correlates with earwax type (wet or dry). People with wet earwax tend to have more active apocrine glands and higher likelihood of underarm odor. Approximately 16 percent of Japanese people have wet earwax, compared to about 90 percent of Western populations.
Aging Odor - The Truth About Nonenal
Aging Odor Intensifies from the 40s
The causative compound of aging odor is 2-nonenal, an unsaturated aldehyde. It is generated when palmitoleic acid (9-hexadecenoic acid) secreted from sebaceous glands undergoes oxidative decomposition by lipid peroxides. Palmitoleic acid secretion increases from the 40s, and simultaneously the body's antioxidant capacity declines, leading to increased nonenal production.
Areas Where Aging Odor Develops
Areas rich in sebaceous glands - the scalp, behind the ears, back of the neck, and upper back - are the primary sources of aging odor. Behind the ears and back of the neck are particularly difficult to notice yourself, and many people only become aware when others point it out. If your pillow starts to smell, it is a sign that aging odor has begun.
Countermeasures for Aging Odor
The fundamentals of aging odor management are preventing sebum oxidation and keeping source areas clean. Actively consume antioxidants (vitamin C, vitamin E, polyphenols) through diet to reduce oxidative stress. During bathing, carefully wash behind the ears, back of the neck, and back. However, over-washing triggers excess sebum production, so choose mildly acidic body wash and avoid scrubbing.
Stress Odor - The Unique Smell Released Under Tension
The Mechanism of Stress Odor
"Stress odor," discovered by a Shiseido research team in 2018, is a distinctive smell released from the skin when feeling tension or stress. Its main components are dimethyl trisulfide (DMTS) and allyl mercaptan, which have a pungent sulfurous odor. It occurs through a different mechanism than normal sweat odor or aging odor - rather than being secreted from eccrine or apocrine glands, it is released directly as skin gas.
Stress Odor Affects Those Around You
Interestingly, research shows that people who smell stress odor also tend to experience increased fatigue and confusion. This means stress odor may unconsciously signal to others that "I am tense." The concern about body odor during interviews or business meetings may involve this stress odor.
Dealing with Stress Odor
Antiperspirants cannot prevent stress odor. The fundamental solution is reducing stress itself, but for immediate relief, deep breathing (4-7-8 breathing technique) or cooling the wrists with cold water can suppress sympathetic nervous system arousal. Masking with perfume or deodorant serves as a temporary measure. (Books on stress management offer detailed guidance on regulating the autonomic nervous system)
How Diet Affects Body Odor
Animal Protein and Body Odor
Animal proteins abundant in meat produce odorous substances like indole, skatole, and hydrogen sulfide during intestinal decomposition. These are absorbed from the intestinal tract into the bloodstream and excreted through sweat and breath. A meat-heavy diet tends to intensify body odor.
Alcohol and Garlic
Alcohol is broken down into acetaldehyde in the liver, and some is excreted through sweat and breath. Allicin in garlic is converted to allyl methyl sulfide after digestion and absorption, then released from the entire body via the bloodstream. These are temporary but can persist until the next day.
Foods That Reduce Body Odor
Catechins in green tea have deodorizing and antibacterial properties. Fiber-rich vegetables and fruits improve gut environment and suppress production of intestinal odor compounds. Foods containing citric acid like pickled plums and lemons can reduce ammonia concentration in sweat.
Proper Use of Antiperspirants and Deodorants
The Difference Between Antiperspirants and Deodorants
Antiperspirants physically block sweat gland openings with ingredients like aluminum chloride, reducing sweat volume. Deodorants suppress bacterial growth with antimicrobial ingredients, preventing odor generation. Most commercial products combine both functions.
The Best Time to Apply Is at Night
For maximum antiperspirant effectiveness, apply to clean skin before bed. Nighttime sweat production is low, allowing active ingredients to better penetrate sweat glands. Reapplication in the morning is unnecessary, and effectiveness persists even after showering. Incorporating it into your nighttime routine is more rational than rushing to apply before going out in the morning.
Caution Against Overuse
Using antiperspirant excessively over the entire body may affect thermoregulation. Limit use to localized areas like the armpits and avoid full-body application. Aluminum chloride can cause skin irritation, so those with sensitive skin should start with lower-concentration products. (Books on body odor management offer detailed guidance on choosing antiperspirants)
Clothing Odor Management - An Often-Overlooked Blind Spot
Bacteria Embedded in Clothing Become Odor Sources
Body odor comes not only from skin but significantly from bacteria and sebum accumulated in clothing. Synthetic fabrics like polyester are more prone to bacterial adhesion and growth compared to cotton, and odors persist more readily. During sweaty seasons, choosing natural fiber undergarments like cotton or merino wool can reduce odor accumulation.
Dealing with Odors That Regular Washing Cannot Remove
For clothing odors that regular washing cannot eliminate, soaking in oxygen-based bleach (sodium percarbonate) dissolved in 40 to 50 degree Celsius water for 30 minutes to 1 hour is effective. Avoid chlorine bleach on colored items as it damages fibers.
Summary - Bacterial Control Is the Core of Body Odor Management
The essence of body odor is metabolic byproducts from skin bacteria breaking down sweat and sebum. Controlling bacterial growth environments is a more rational approach than trying to stop sweating. By combining hygiene maintenance, proper antiperspirant use, dietary improvements, and stress management, body odor can be reliably controlled.