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sweat rate remains underexplored and underrated in clinical medicine. However, with the emergence and
continuous advancements of sweat analyzing wearables, sweat rate analysis holds the potential to become a
clinically, broadly available digital biomarker. In this Comment, we introduce and discuss the sweat rate as a
promising novel digital biomarker to monitor health and disease in clinical medicine beyond sports science.

THE SWEAT RATE PHYSIOLOGY
Basics
[6,7]
The human body houses approximately two to four million sweat glands . Eccrine, apocrine, and
[8,9]
apoeccrine sweat glands can be distinguished . While eccrine sweat glands are responsible for the highest
volume of sweat excretion , secretion of apocrine and apoeccrine glands can also influence the sweat
[10]
composition at the skin surface . During sweating, up to 2,426 J of heat per gram of evaporated sweat can
[11]
be dissipated from the body . Aiming to maintain thermoregulation, sweating is the most efficient way to
[12]
[13]
dissipate heat from the body. Next to heat stress, sweat glands can be stimulated by emotional stress ,
mechanical vibration , eating spicy food (gustatory hyperhidrosis) , or chemical substances such as
[14]
[15]
[16]
carbachol and local current .
Neurological control
[17]
Many thermosensitive neurons can be found in the preoptic area and the anterior hypothalamus . To keep
the body temperature constant, they initiate appropriate responses when detecting changes in body
temperature . Augmented local preoptic temperature or a rise in afferent impulses from the cutaneous and
[17]
[17]
spinal thermoreceptors caused by elevated skin temperature can both result in increased sweating .
However, increased core body temperature stimulates the sweat rate nine times more efficiently than
increased mean skin temperature [18-20] .

Body map
Local sweat rates for the mid-front, sides, and mid-later back were found to be significantly higher in males
compared to females . In both sexes, the highest sweating was observed along the spine, whereas the sweat
[21]
rate on the upper arm was lowest. Furthermore, total sweating on the back exceeded the total sweating of
the chest.

For older males, gross sweat loss and regional sweat rates were significantly lower compared to the
young . During rest, significantly lower regional sweat rates at almost all body regions were observed,
[22]
[22]
whereas, during exercise, a significant difference was found for the hands, legs, ankles, and feet .
Influencing variables
Environmental factors such as ambient temperature, air velocity, and radiant load, along with factors such
as clothing and the level of physical activity, influence the sweating rate [Figure 1] .
[23]

Heat acclimatization of five to eight days results in thermoregulatory adaptions such as increased sweat rate
and earlier onset of sweating . However, depending on humid or dry heat exposure, the adaptation of the
[24]
eccrine sweat gland differs: the sweat rate in a hot-humid environment is greater than in a hot-dry
[24]
environment . In healthy unacclimatized men, a sweating capacity of maximally 1.5 liters per hour has
been reported, whereas, in highly trained acclimatized soldiers, a sweat rate of two to three liters per hour
[25]
was reached . Sweat rates of one liter per hour occur frequently depending on factors like the environment
or the intensity of exertion; however, sweat rates can vary considerably . Not only heat acclimatization but
[26]
[26]
also training can lead to an increase of sweat rates of 200 to 300 mL per hour .