I’m glad you asked this! I’d been meaning to look up some stuff about sweat. The wikipedia says:

sodium 0.9 gram/liter
potassium 0.2 gram/liter
calcium 0.015 gram/liter
magnesium 0.0013 gram/liter

Also many other trace elements are excreted in sweat, again an indication of their concentration is (although measurements can vary fifteenfold):
zinc (0.4 mg/l)
copper (0.3 – 0.8 mg/l)
iron (1 mg/l)
chromium (0.1 mg/l)
nickel (0.05 mg/l)
lead (0.05 mg/l).
Probably many other less abundant trace minerals will leave the body through sweating with correspondingly lower concentrations.

Interesting. So it is primarily the sodium that we take in (and I think potassium is the main ingredient in salt ‘alternatives’).

Mostly, though, sweat is NaCl, and water.

@syz The sodium and potassium ratios in our body are very important, meaning how much potassium to salt, when this is out of balance it can cause heart arythmia and death. You will hear it called electrolyte (salt) imbalance. I would bet our bodies try to adjust to a perfect balance by slightly changing the ratios we lose through sweat and urine, depending on how much we have ingested and how much water is in our body, but I am not a scientist or doctor.

Sweat also contains androstenone which might act as a pheromone.