By Sebastian Madlangbayan, founder of Cleonse: the world's cleanest 3-ingredient organic electrolyte.
Drink 16–20 oz of water in the hour before your sauna, then replace 125–150% of the weight you lost afterward with fluid that contains sodium. A typical session sheds about 0.5 kg of sweat, carrying roughly 200–1,000mg of sodium with it. Water alone leaves that unreplaced.
That's the short version. The longer version is worth reading, because sauna is one of the few situations where the sweat loss is real, the exercise stress is not, and most people's instinct — chug water — is the least useful response.
What a sauna session actually costs you
Sauna sweat is not a mystery. It has been measured.
A traditional Finnish sauna runs at 80–100°C with relative humidity of 10–20%, with exposures typically lasting 5–20 minutes per round. Infrared cabins run considerably cooler, generally 45–60°C. Those numbers come from a 2018 systematic review of dry sauna bathing in Evidence-Based Complementary and Alternative Medicine.
At those temperatures, sweat is secreted at a rate of 0.6 to 1.0 kg per hour at 80°C to 90°C, with an average total secretion of 0.5 kg during a warm sauna bathing session. That figure comes from correspondence in Mayo Clinic Proceedings by the researchers behind the large Finnish sauna cohort studies.
Half a kilogram is roughly half a liter — about a pint. That is the number to anchor on, and it's smaller than sauna culture tends to imply. A three-round session with cool-downs might push you to 0.7–1.0 L. A single 15-minute round will be well under half of that.
Turning fluid loss into sodium loss
Sweat sodium concentration varies enormously between people. Precision Fuel & Hydration, drawing on a database of more than 30,000 sweat tests, puts the range at roughly 200 to 2,300 mg of sodium per liter of sweat, with a typical athlete around 950 mg/L.
Multiply the two and you get your actual sodium cost:
| Session | Sweat lost | Low-sodium sweater (200 mg/L) | Average (950 mg/L) | Salty sweater (2,000 mg/L) |
|---|---|---|---|---|
| One 15-min round | ~0.25 L | 50mg | 240mg | 500mg |
| Standard session (~0.5 kg) | ~0.5 L | 100mg | 475mg | 1,000mg |
| Long multi-round session | ~1.0 L | 200mg | 950mg | 2,000mg |
| Sauna after a hard workout | 1.5–2.5 L total | 300–500mg | 1,400–2,400mg | 3,000–5,000mg |
Two honest observations from that table.
First, for a single standard session, the average person loses somewhere in the neighborhood of 400–500mg of sodium. That is not nothing, and it is not a crisis. It's roughly what's in a single serving of a moderately dosed electrolyte mix.
Second, the spread is enormous. A salty sweater doing a long session loses ten times what a low-sodium sweater loses in one round. This is why generic sauna hydration advice is useless and why the honest answer to "how much do I need" is always "it depends on you."
Before the sauna
Go in already hydrated. Not overloaded — hydrated.
Practically, that means 16–20 oz of water in the hour beforehand, and not walking in on the back of a long day where you've had two coffees and no water. If your urine is dark going in, drink before you sit down.
You generally do not need sodium before a sauna the way you might before a long run in the heat. The session is short, you're not producing metabolic heat, and there's no performance you're protecting. The exception is if you're going in already depleted — after a long training session, a long flight, a hot day outdoors — in which case front-loading some sodium makes sense because you're starting from a deficit, not because of the sauna itself.
Skip alcohol. This one isn't controversial. Alcohol is a diuretic, it impairs thermoregulation, and the Finnish sauna literature consistently flags it as the main risk factor in sauna-related incidents.
After the sauna: the actual protocol
Here is where the science is clearest and most people get it wrong.
Step 1: Weigh yourself before and after, at least once. Do this a couple of times and you'll know your personal number. One kilogram of body mass lost is approximately one liter of sweat. You only need to do this a few times to calibrate; after that you'll know what your session costs.
Step 2: Drink 125–150% of what you lost. This is the counterintuitive part. Replacing exactly the volume you lost does not restore fluid balance, because you continue to produce urine while you rehydrate. Research on post-exercise rehydration consistently finds that a volume equivalent to 100% of body mass loss leaves people in deficit, and that 150% replacement is what actually restores balance. If you lost 0.5 kg, drink 0.6–0.75 L over the following hour or two. Not all at once.
Step 3: Include sodium in that fluid. This is the part water can't do. Sodium is what makes the fluid stay. The mechanism is straightforward: raising blood sodium concentration and osmolality stimulates renal water reabsorption and reduces urine output, so more of what you drink is retained rather than passed.
The Gatorade Sports Science Institute's review of beverage formulation puts specific numbers on this. Fluid retention is significantly improved by drinking a beverage with a sodium concentration of at least 20–30 mmol/L compared with no-sodium or very-low-sodium drinks. Below that, you're mostly making urine.
There's also an upper bound worth knowing. The same review notes that 18–40 mmol/L improves palatability and increases how much people voluntarily drink, while concentrations at or above 50 mmol/L can reduce palatability and voluntary intake. A drink that's too salty gets abandoned half-finished, which defeats the purpose.
What those concentrations look like in real products
| Product | Sodium per serving | Water volume | Concentration |
|---|---|---|---|
| Plain water | 0mg | — | 0 mmol/L |
| Gatorade Thirst Quencher stick | 230mg | 16.9 oz (500 ml) | ~20 mmol/L |
| Powerade | 240mg | 12 oz (355 ml) | ~29 mmol/L |
| Skratch Labs Hydration | 400mg | 16 oz (473 ml) | ~37 mmol/L |
| Cleonse | 500mg | 16 oz (473 ml) | ~46 mmol/L |
| LMNT | 1,000mg | 16 oz (473 ml) | ~92 mmol/L |
Cleonse sits at roughly 46 mmol/L — above the retention threshold, near the top of the palatable band, below the point where intake starts to drop off. A 1,000mg-per-16-oz product is about double that. That isn't a knock on high-dose products; it's a reason to dilute them into more water if you're using them for straightforward rehydration rather than replacing a very large loss.
Why carbohydrate matters after a long session
Sodium is the headline, but if your sauna session was long, or stacked on the back of training, carbohydrate earns its place too.
Two reasons. The first is absorption: glucose and sodium are co-transported across the intestinal wall, and the presence of glucose speeds sodium and water uptake. The second is simply that a warm sweet drink after heat is something people finish, and a rehydration drink you don't finish doesn't work.
There's a third reason that's less about physiology and more about how people actually use saunas. Plenty of sauna sessions happen after a workout, after a long run, at the end of a hard day. In those cases you're not just replacing sweat, you're refueling. A zero-calorie electrolyte does the first job and none of the second.
For a short standalone session in an infrared cabin, you probably don't need the carbohydrate. For 30–45 minutes of rounds in a traditional Finnish sauna after training, you likely do.
Honest product picks
There is no single best electrolyte for sauna. There are good fits for different situations.
If you're a heavy or salty sweater doing long sessions: a high-sodium product like LMNT (1,000mg sodium, zero sugar, stevia-sweetened) covers the largest losses in one serving. If you dislike stevia, LMNT Raw Unflavored has none.
If you want a sports-science pedigree and moderate everything: Skratch Labs Hydration Sport Drink Mix — 400mg sodium, 80 calories, real cane sugar and dextrose, built by an exercise physiologist for endurance athletes.
If you're just doing a session and want water that stays put: honestly, a pinch of good salt in a glass of water and something to eat will cover it. I'm not going to pretend you need a product for a single 15-minute round.
If you want a post-sauna refuel with a short label: that's what I built Cleonse for. Three ingredients — organic lemon or strawberry powder, organic cane sugar, and French grey sea salt. 500mg of sodium and 26g of carbohydrate from 24g of organic cane sugar in 16 oz of water. 100 calories. 85+ trace minerals from the salt itself rather than added mineral compounds. No stevia, no artificial sweeteners or flavors, no dyes, no preservatives, no gums, no fillers. Vegan and gluten-free.
I built it for exactly this kind of use — fluid, sodium, and fuel in one glass, with a label you can read in three seconds. It is a moderate sodium dose, not a maximal one. If you're losing 2,000mg in a session, one stick isn't going to cover it, and I'd rather say so than pretend otherwise.
A note on what sauna won't do
Sauna is genuinely interesting from a cardiovascular research standpoint, and the Finnish cohort studies are worth reading. But two claims deserve pushback.
Weight loss. The kilogram you're down after a session is water. It comes back with the next glass you drink. That's not a criticism of sauna, it's just what fluid loss is.
Detoxification. The concentrations of metals and other compounds found in sweat are quite low, and the liver and kidneys remove far more than the sweat glands do. The researchers who study sauna say this themselves in the Mayo Clinic Proceedings correspondence cited above. Replacing what you sweated out is a sound reason to drink electrolytes after a sauna. Flushing toxins is not.
Try The World's Cleanest Electrolyte™
Three ingredients. 500mg sodium. Nothing artificial. Free shipping and a 30-day guarantee.
Shop CleonseFrequently asked questions
Do you need electrolytes after a sauna? For a standard session — roughly 0.5 kg of sweat — you're losing somewhere around 200 to 1,000mg of sodium depending on how salty your sweat is. Replacing that with a sodium-containing drink helps you retain the fluid you drink rather than pass it. For a single short round, water and a normal meal will usually cover it.
How much water should you drink after a sauna? Replace 125–150% of the body mass you lost, spread over the following hour or two. Research on post-exercise rehydration consistently shows that replacing only 100% of the loss leaves you in deficit, because you keep producing urine while rehydrating. Weigh yourself before and after a few times to learn your own number.
Should you drink electrolytes before or after a sauna? After, primarily. Go in normally hydrated with 16–20 oz of water in the preceding hour, and save the sodium for afterward when you have an actual loss to replace. The exception is going in already depleted — after training, travel, or a hot day — where front-loading sodium makes sense.
Is Gatorade good after a sauna? It works, in that it contains sodium and carbohydrate. At about 20 mmol/L it sits at the low end of the range shown to improve fluid retention, so you'd need a decent volume. The common objection is label quality rather than function — several Gatorade products still list synthetic dyes, though PepsiCo is in the middle of phasing those out.
Can you drink too many electrolytes after a sauna? You can drink too much fluid, which is the more relevant risk. Exercise-associated hyponatremia is driven primarily by overconsumption of fluid rather than sodium deficiency. Drinking to thirst plus a deliberate top-up to cover measured loss is a sound approach; forcing down liters because it feels virtuous is not.
Does sauna sweat contain the same electrolytes as exercise sweat? Broadly yes. It's eccrine sweat in both cases, and intensive sweating increases loss of water, sodium, potassium, chloride, urea, and lactate. The difference is the volume and the context: sauna sweat happens without the glycogen depletion, muscle damage, and prolonged cardiovascular load of exercise.
Cleonse: three ingredients, 500mg sodium, 26g carbohydrate from organic cane sugar, mixed into 16 oz of water. Built for the glass you drink after. $33 for 10 sticks, $66 for 30, $110 for 60, free shipping, 30-day guarantee. See the product.
Editor's note and sources
I founded Cleonse, one of the products recommended above. Competitor figures were read from current public product pages and manufacturer sites in July 2026. Sauna sweat rates are population figures from published research and will not match any individual — weigh yourself if you want your real number. Trace mineral counts are sourcing claims and are not independently verified here. Formulas and prices change; check the label you're holding.
- Sweat secretion rate and total secretion during sauna bathing, Mayo Clinic Proceedings (Kunutsor & Laukkanen correspondence): https://www.mayoclinicproceedings.org/article/S0025-6196(18)31013-9/fulltext
- Hussain J. & Cohen M., "Clinical Effects of Regular Dry Sauna Bathing: A Systematic Review," Evidence-Based Complementary and Alternative Medicine 2018: https://onlinelibrary.wiley.com/doi/10.1155/2018/1857413
- Sweat sodium concentration range and estimation method, Precision Fuel & Hydration: https://www.precisionhydration.com/performance-advice/hydration/how-to-estimate-sweat-salt-loss/
- Beverage sodium concentration and fluid retention thresholds, Gatorade Sports Science Institute, Sports Science Exchange: https://www.gssiweb.org/sports-science-exchange/article/the-fluid-replacement-process-principles-of-beverage-formulation-for-athletes
- Hew-Butler T. et al., "Exercise-Associated Hyponatremia: 2017 Update," Frontiers in Medicine: https://www.frontiersin.org/journals/medicine/articles/10.3389/fmed.2017.00021/full
- LMNT ingredients and nutrition: https://drinklmnt.com/pages/ingredients
- Skratch Labs Hydration Sport Drink Mix: https://www.skratchlabs.com/products/hydration-sport-drink-mix
Nothing here is medical advice. Cleonse supports hydration; it does not treat, cure, or prevent any condition. If you have cardiovascular disease, are pregnant, or are on sodium-restricted or blood-pressure medication, talk to your doctor before regular sauna use.