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Page 6 of 10 Brasier et al. Soft Sci 2024;4:6 https://dx.doi.org/10.20517/ss.2023.39

SWEATING - A SYMPTOM IN CLINICAL MEDICINE
Sweating is an unspecific but very common symptom in clinical medicine. Currently, the quantification of
the sweat rate can only be conducted during clinical examination in this field. There are several qualitative
measures (the Clinical Opioid Withdrawal Scale and the descriptive observation by the examinator) and
quantitative measures (gravimetrical analysis using technical absorbents and determining changes in the
body weight) that can be employed [51-53] . An easy, continuous, and straightforward measurement of the
sweat rate during everyday life is not yet available. Therefore, the full clinical potential of sweating as a
symptom and an indicator of health and diseases has only been vaguely exploited until recently.

Clinical sweat terminology
To objectively assess the symptom of “sweating”, the sweat rate must be determined. It can be distinguished
between local and whole body sweat rates. The local sweat rate refers to the excretion of sweat on a certain
skin surface, whereas the whole body sweat rate covers the total loss of sweat from the body. Changes of the
sweat rate can (i) result from either physiological and/or pathophysiological changes in the body, referred to
as non-iatrogenic; or (ii) be induced in the body, for example, by pharmacological therapy, referred to as
iatrogenic. The sweat rate may be increased above the physiological need in regard to maintaining
[54]
thermoregulation, named hyperhidrosis, or decreased, named hypohydrosis . When there is no sweat
excretion at all, it is called anhidrosis. Derived from common medical terminology, changes in the sweat
rate are classified as focal if a limited area on the body surface is affected or generalized if the whole-body
surface is presumed to be affected. Changes in the sweat rate are categorized to be primary when originating
within the functional chain of the sweat gland or secondary when induced by external variables affecting the
[55]
sweat gland chain [Table 2] .

Clinical sweat monitoring
Both the local and the whole body sweat loss assessments are not continuously feasible and need lab
infrastructure. Wearable sweat analysis to assess hydration during exertion or in hot environments is
[37]
convenient and affordable . These wearable sweat sensors enable sweat rate monitoring and can
additionally assess changes in electrolyte concentration such as sodium, chloride, and additional biomarkers
of interest [46,56] . By being coupled to smartphones, wearable sweat sensors provide a straightforward
opportunity to continuously assess the local sweat rate. This, in turn, makes it possible to extrapolate the
whole body sweat loss . Furthermore, learning algorithms enable direct data interpretation and use within
[56]
predictive models to establish preventive measures or to adapt therapies.

Sweat in clinical medicine
Hyperhidrosis
Primary hyperhidrosis is an idiopathic condition that occurs in 4.8% of the U.S. population. The lead
symptom is excessive sweating. The most affected regions are the plantar, palmar, and axillary regions of the
body [57,58] . While not primarily being life-threatening, primary hyperhidrosis directly affects social life. More
severe causes of hyperhidrosis can be assessed during clinical anamnesis and examination. One of the more
prevalent symptoms of hyperhidrosis is night sweats, which is assessed by inquiring the patients if night
sweats have been observed. The current clinical definition of night sweats is when pajamas had to be
changed during the night as being soaked up wet. Due to the binary nature of the question, only the
affirmative answer leads to documentation and, therefore, implementation into the treatment plan. In many
instances, however, night sweats are not further investigated. Increased night sweats may have several
underlying reasons, such as (i) elevated environmental conditions (temperature/relative humidity); (ii)
infectious diseases such as viral infections with Influenza or COVID-19; and (iii) bacterial infections such as
pneumonia and even tuberculosis. Additionally, night sweats may appear in cases of (iv) autoimmune
diseases or (v) cancer. Also, (vi) hormone changes, such as those seen in hyperthyroidism; (vii) genetical