salt in sweat...

[dtvonly]

why is there salt in sweat? there is also a small amount of sugar and urea. So why is salt so "dominant" in our sweat to the point that we can taste is? Why not sweet sweat? please explain the physiological significance of (more) salt in our sweat. Thank you.

Edited May 5, 2017 by dtvonly

[Function]

I'm not 100% sure, but common sense (or some physiology-sense) says that NaCl flows together with water so this would lead me to think that there's just a lot more of NaCl in sweat than glucose ...

[CharonY]

The ultimate composition of sweat varies quite a lot and is the result of various absorption and reabsorption processes. However, the salt concentration should be roughly related to plasma levels. The concentration of sodium in plasma is about 140 mmol/L, that of sweat is somewhat diluted to ~40 mmol/L on average (exertion/ hydration level etc. change this value.

Glucose on the other hand tends to be roughly in low mmol/L (1-5.5, depending on paper) in sweat as well as plasma. So it tends to be proportionately higher, actually. This discrepancy could also be explained by different methods used in different sweat studies, but it is clear that there is not an enrichment of salt in sweat (also note that the other salts, also found in plasma contribute to taste).

[StringJunky]

The ultimate composition of sweat varies quite a lot and is the result of various absorption and reabsorption processes. However, the salt concentration should be roughly related to plasma levels. The concentration of sodium in plasma is about 140 mmol/L, that of sweat is somewhat diluted to ~40 mmol/L on average (exertion/ hydration level etc. change this value.

Glucose on the other hand tends to be roughly in low mmol/L (1-5.5, depending on paper) in sweat as well as plasma. So it tends to be proportionately higher, actually. This discrepancy could also be explained by different methods used in different sweat studies, but it is clear that there is not an enrichment of salt in sweat (also note that the other salts, also found in plasma contribute to taste).

Won't salt become concentrated by simple evaporation on the skin?

[CharonY]

That too. The indicated concentrations were based on direct collection of sweat.

[StringJunky]

That too. The indicated concentrations were based on direct collection of sweat.

Right.

[Sriman Dutta]

Salt is more soluble in water than most other substances in the body. So the excretion of water involves removal of salts too.