Sweat and odor — the whole picture
Concerns about sweat and odor divide into two: the amount of sweat (hyperhidrosis) and the quality of odor (bromhidrosis, age-related odor). The causes and the responses are different, though many men carry both. The starting point is to separate which one you are actually worried about.
Why it happens — the mechanism
The amount of sweat (hyperhidrosis)
Sweat is released from eccrine glands on signals from the sympathetic nervous system. Most hyperhidrosis is "primary focal" — the sympathetic system over-responds beyond what temperature regulation requires, limited to the palms, soles, underarms, or scalp, and tends to intensify in situations of tension or anxiety. It is strongly constitutional and genetic — not a matter of hygiene or effort. There is also "secondary" hyperhidrosis caused by medication or thyroid conditions; if you sweat heavily over the whole body or it started suddenly, the background is worth checking.
The quality of odor (bromhidrosis)
The lead actor in underarm odor is the apocrine gland, not the eccrine gland. What apocrine glands secrete is nearly odorless on its own; the odor is created when skin bacteria (such as corynebacteria) break it down. The number and activity of apocrine glands is strongly genetic, and is known to correlate with having damp earwax.
Age-related odor
On a separate axis, age-related odor is mainly attributed to nonenal, formed when fatty acids in sebum oxidize, and tends to increase with age.
What makes it worse
- Tension, anxiety, being watched (emotional sweating)
- Heat trapped by poorly ventilated clothing or fabrics
- Leaving a damp environment where bacteria multiply
- Changes in sebum and metabolism from lack of sleep, smoking, or diet
Common misconceptions
- Sweating ≠ being unclean. Hyperhidrosis is constitutional, not a hygiene problem.
- Odor doesn't simply wash away. The cause is bacterial breakdown, not the secretion itself, so washing alone tends to let it return.
- "Antiperspirant doesn't work" ≠ severe. Ingredient, concentration, and timing change the result.
Japan vs. overseas — a difference in view
Body-odor constitution differs by genetics. The gene that decides wet vs. dry earwax (ABCC11) means a higher proportion of East Asians have weaker apocrine odor, while it tends to be stronger among people of European and African descent.
Partly for that reason, deodorant use is established as a near-necessity of daily life in the West, while in Japan the cultural pressure of "do I smell more than others?" tends to weigh heavier. Choosing a surgical response — as with "bromhidrosis surgery" — is more prominent in Japan and Korea than in the West. So even with the same sweat and odor, what counts as "the problem" differs by culture.
A map of options (as layers, not steps)
Doing nothing / lifestyle adjustments (absorbent fabrics, changing clothes) / over-the-counter antiperspirants (aluminium chloride, etc.) / topical and insured treatment at a dermatologist / out-of-pocket procedures such as botulinum toxin or microwave / surgery. The higher you go, the more irreversible and costly. You do not have to climb in order — choose by how much it affects your life.