Classically, sweating was thought to occur when our skin temperature elevates past its normal range. In the 1800’s this theory was put to bed when brain temperature was discovered to be a better predictor of one’s perspiration response. The portion of the brain responsible for sensing our internal temperature is called the hypothalimus. It is particularly old by evolutionary standards, and yet this region controls a wide variety of other involuntary responses including sleep, thirst, hunger, development, shivering and even pupil dilation. Currently, scientists think that transmission between the temperature receptors of the hypothalimus and the sweat glands initiate perspiration.
The main biomolecule involved in the sweat response is acetylcholine. Acetylcholine has the distinction of been the first neurotransmitter ever discovered (circa 1914). Its profound influence over the sweat response has been demonstrated in multiple randomized controlled trials in which drug treatment was compared against placebo. Treatment groups were given a potent acetylcholine antagonist called onabotulinumtoxina (i.e. Botox) in the form of a low dose injection. Most of these studies demonstrated a greater than 50% reduction in perspiration on average. Based on these results, although the hypothalimus may initiate sweating, blocking acetylcholine receptors on the sweat glands themselves dampens the response.
The effects of acetylcholine on the inner workings of the central nervous system is also quite interesting. It is thought that acetylcholine supports brain function and may even delay the onset of neurological diseases. In fact, the most commonly prescribed medications for Alzheimer’s disease work by preventing the breakdown of this neurotransmitter. Healthy brains benefit too. Acetylcholine cascades within the cerebral cortex also enhances the fidelity of REM wave patterns during sleep. Dexterity and habit formation is also thought to be influenced (in part) by acetylcholine in the basal ganglia. Perhaps this phenomenon helps explain why people like me tend to get hooked on physical yoga. Perspiration is merely the consequence of an elaborate neuromodulatory orchestration.