Sweat Composition Basics
Sweat is roughly 99% water and 1% dissolved substances. The dissolved component is mostly sodium and chloride - table salt, essentially - with smaller amounts of potassium, calcium, magnesium, lactate, urea, and trace amounts of other compounds.
Sodium concentration in sweat is by far the most variable. Published research has reported sweat sodium anywhere from around 200 mg/L on the low end to over 1,500 mg/L on the high end, depending on the individual and the conditions. That's a 7× range.
Why People Differ So Much
Genetics play a part - "salty sweaters" tend to be a stable trait, with friends or family often noting white salt residue on caps and shirts. Diet plays a part - chronic sodium intake adjusts the body's set-points over time. Heat acclimatisation plays a part - well-acclimatised athletes tend to sweat earlier, more, and slightly less salty than poorly-acclimatised athletes in the same conditions.
The practical implication: a generic "how much sodium do I need per hour" number is a starting point, not a precision answer.
Sweat Rate vs Sweat Composition
Two separate variables. You can sweat heavily without sweating saltily, and vice versa. Sweat rate scales with metabolic heat production and environmental conditions - typical sport-context rates are 0.5-1.5 L/hour for trained athletes. Sweat composition is more genetically anchored.
Replacing What You Lose
For sessions under an hour in mild conditions, water and a normal day of eating cover replacement. For longer sessions or hot conditions, the ACSM has long suggested in-session intake of around 0.4-0.8 L of fluid per hour with sodium-containing drinks for sessions over an hour. When Do You Actually Need Electrolytes? walks through this in practice.
The exact dose is something many endurance athletes refine over time - through trial in training, observation, and (for some) lab sweat testing offered by specialty endurance retailers.
White Salt Stains Aren't Always Bad News
Visible salt residue on a cap or jersey after a hot session is a sign that you're a saltier-than-average sweater. It's not a problem on its own - it's information. Higher-sodium electrolyte products (LMNT, the higher-end Liquid I.V. dosing) tend to suit this profile better than lighter daily-hydration formats.
Sources
Authoritative references this article draws on. External links open in a new tab.
Frequently Asked
Why do some people sweat more than others?
Body size, fitness level, heat acclimatisation, hydration status, and genetics all contribute. Why some people sweat more walks through each variable.
Is salty sweat a problem?
Not on its own - it's just an individual trait. People with saltier-than-average sweat tend to benefit from higher-sodium electrolyte products, particularly during long or hot training sessions.
Can I test my sweat composition?
Yes - lab sweat testing is offered by some endurance specialty retailers and sports performance labs in Australia. Precision Fuel & Hydration and select clinics provide the service.
Does sweating mean I'm 'detoxing'?
Not really, in any meaningful sense. The body uses urine and stool for waste, not sweat. Sweat is primarily a temperature-regulation mechanism.
