Focal Assessment · Classification · CityLink Mall
Hyperhidrosis is not a hygiene failure and not a surplus of sweat glands. It is a sympathetic signalling problem — normal glands receiving an instruction that is out of proportion to the thermal demand — and the first thing that has to be settled is whether the cause is the nerve or something behind it.
Eccrine sweat glands are distributed across almost the whole body surface and exist for thermoregulation — evaporative cooling is the only efficient mechanism the human body has for shedding heat. They are controlled by the sympathetic nervous system, but unusually among sympathetic targets they are driven by acetylcholine rather than noradrenaline. That single fact is why the condition behaves as it does and why the interventions that work, work.
In hyperhidrosis the glands themselves are structurally normal. They are not more numerous, not enlarged, and not diseased. What is abnormal is the volume of the instruction arriving along the sympathetic chain. Thermoregulatory sweating is governed by the hypothalamus in response to core temperature; emotional sweating is driven separately, through limbic pathways, and is why palms and axillae respond to anticipation, scrutiny and stress rather than to heat. In primary focal hyperhidrosis that emotional pathway appears to be set at an inappropriately low threshold.
This distinction explains the pattern patients describe. Sweating that arrives before the meeting rather than during it, that is worst in an air-conditioned office and better on a hot walk, that is confined to two or three sites while the rest of the body stays dry — none of that is consistent with a heat problem, and all of it is consistent with a signalling one. In Singapore's climate the picture is often obscured, because ambient humidity keeps evaporation inefficient and everybody sweats; the useful question is not how much, but where, when, and whether it is symmetrical.
The corollary matters as much as the mechanism. Because the neurotransmitter at the neuroglandular junction is acetylcholine, an agent that prevents acetylcholine release will silence the gland without damaging it, without touching sensation, and without affecting the glands beyond the treated field. The gland is left intact and the instruction is interrupted — which is also why the effect is temporary and why it returns as nerve terminals recover.
Classification
Everything about the management of excessive sweating follows from one distinction, and it is made from the history rather than from any test. Primary focal hyperhidrosis is a benign disorder of signalling in otherwise healthy people. Secondary hyperhidrosis is a symptom of something else, and treating the sweat while ignoring the cause is the single most serious error available on this subject.
Sweating that wakes you at night, or that started in adulthood, is a symptom to investigate — not a cosmetic problem to inject.
The Decision
The consultation is not principally about how much you sweat. It is about onset, distribution, symmetry, whether it stops when you sleep, what medications you take and whether anything else has changed — because those answers separate a benign focal disorder from a presenting symptom, and nothing should be injected until they have been asked. Where the pattern is at all atypical, bloods and a referral come before any treatment is discussed.
Once primary focal hyperhidrosis is established, the practical questions are which sites are affected and how severely the sweating interferes with work, clothing and social function. Severity here is measured in consequences rather than millilitres: ruined shirts, avoided handshakes, paper that will not stay dry, a wardrobe restricted to two colours. Antiperspirants containing aluminium salts are the reasonable first line and are genuinely effective for milder axillary cases; they fail on palms and soles, where the stratum corneum is thick and the surface is constantly abraded.
Botulinum toxin is well established for axillary and palmar hyperhidrosis, and it works by preventing acetylcholine release at the neuroglandular junction rather than by damaging anything. The field is mapped before injection — starch-iodine testing makes the active zone visible where it is not obvious — and the palms require more care than the axillae, because the same neurotransmitter serves the small muscles of the hand and grip strength is a real consideration. The effect is finite and the treatment is repeatable, which is an honest limitation rather than a hidden one.
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