What to Drink After an Infrared Sauna (and How Much)

How Much Fluid Does an Infrared Sauna Session Cost?

A 45-minute infrared session typically costs about 0.4 to 1.0 kg of sweat, and cabin temperature explains most of the spread. Two recent studies measured it the reliable way, by weighing people before and after.

At the University of Oregon, Atencio and colleagues ran 20 healthy young adults through three kinds of passive heating. A 45-minute far-infrared session on a 45 to 65 C (113-149 F) ramp cost 0.39 kg on average, against 0.66 kg for a traditional sauna and 0.90 kg for a hot tub. Participants could drink, and losses were corrected for it. A 2026 Cardiff Metropolitan University study ran the cabin hotter, at about 64 C (147 F) for 45 minutes with no drinking: body mass fell by 1.0 kg (a sweat rate of 1.4 L per hour), plasma volume shrank by 11.6%, 2 of 12 participants passed 2% dehydration, and two could not finish.

Both studies used young, healthy volunteers, so treat these as reference points. Home cabins usually run at 120-150 F; a 20-minute session at the low end will normally cost less than the Oregon figure, while a long one near the top of the dial can match Cardiff. Our guide to how long to stay in an infrared sauna covers duration by experience level.

The scale method: measure your own sweat loss

The American College of Sports Medicine (ACSM) position stand on fluid replacement recommends estimating sweat loss from body weight before and after activity, and it works the same way in a sauna. A liter of sweat weighs about 1 kg (1 lb is about 16 oz).

1. Pee, then weigh yourself without clothes on a digital scale.
2. Note how much you drink during the session.
3. Towel off and weigh again before you drink or pee.
4. Sweat loss is your weight before, minus your weight after, plus what you drank. Divide by your starting weight for a percentage.

For example: 70.0 kg before, 250 ml drunk, 69.4 kg after. That is 0.6 kg plus 0.25 L, so about 0.85 L of sweat, or 1.2% of body weight. Two or three weigh-ins give you a personal number. The ACSM aims to keep the water deficit under 2% of body weight (1.4 kg at 70 kg), so a session that gets close to that calls for drinking during it next time, or a shorter one.

The weight you lose in a sauna is water

Whatever the scale shows after a session is water, and it returns as soon as you drink. The 0.4-1.0 kg above is sweat, not fat; the real calorie cost of a session is far smaller, as our honest look at infrared sauna weight loss explains. Skipping drinks afterwards to keep the number down only leaves you dehydrated.

What Is Actually in Your Sweat?

Sweat is mostly water, and sodium is the only electrolyte it carries in amounts worth replacing. Baker's 2019 review of sweat gland physiology puts whole-body sweat at roughly 20-80 mmol/L of sodium (460-1,840 mg per liter) and 2-8 mmol/L of potassium (80-310 mg per liter), with calcium, magnesium and trace minerals far lower.

Some people are salty sweaters, and anyone's sweat gets saltier as they sweat faster, because the sweat duct reabsorbs a smaller share of the sodium. Sauna sweat tends toward the low end: Baker notes that sweat sodium is lower with passive heat than with exercise, and that heat-acclimated people conserve more salt.

Against the roughly 3,400 mg of sodium the average American eats per day, according to the FDA, a half-liter session costs about 7-27% of a day's intake, which the next meal covers without planning. A full liter at the salty end costs more than half a day's intake, and that is where a deliberate sodium source makes sense.

Magnesium and zinc get plenty of space in electrolyte marketing, but Baker concludes that sweat-induced deficiencies of trace minerals and vitamins appear to be of minimal risk. Sweat is also a minor exit route for waste and toxicants compared with the kidneys and gut, so there is nothing to flush out by drinking extra.

Water, Sports Drink, Coconut Water or Milk: How They Compare

Any of these replaces the water. What separates them is the sodium, the sugar, and how much of the fluid your body keeps.

Per-liter values calculated from USDA FoodData Central, the Powerade label (240 mg sodium per 12 fl oz) and the WHO ORS formula (75 mmol/L sodium).

Plain water

For a session that cost half a liter or less, water is the right and cheapest answer, because your next meal brings the sodium. In the Beverage Hydration Index trial (Maughan and colleagues, 2016), 72 men each drank a liter of still water and of three other drinks from a list of 13, and their urine was collected for four hours. A sports drink, coffee, tea, cola, lager, orange juice and sparkling water all performed about the same as water.

Milk and oral rehydration solution

Three drinks beat water in that trial: full-fat milk, skim milk and an oral rehydration solution (ORS) left more fluid in the body after two hours, with index scores of 1.50, 1.58 and 1.54 against water's 1.00. The men started fully hydrated, so this measures retention rather than post-sauna recovery, but a glass or two of milk after a long session is a sensible choice if you tolerate dairy.

The WHO ORS formula has 75 mmol/L of sodium (about 1,725 mg per liter), 20 mmol/L of potassium and 13.5 g of glucose per liter, and the glucose helps carry sodium, and with it water, across the small intestine. It was built for diarrhea and is saltier than most sweat, so it fits a loss of 1 kg or more, not an everyday session.

Sports drinks

Powerade's label lists 240 mg of sodium, 80 mg of potassium and 21 g of sugar per 12 fl oz, about 680 mg of sodium and 59 g of sugar per liter, which sits at the low end of sweat sodium. After a hard workout plus a sauna, the sugar is useful fuel. After a quiet 20-minute session it is mostly calories you did not need.

Coconut water

Coconut water's electrolyte is potassium. USDA lists 105 mg of sodium and 250 mg of potassium per 100 g for fresh coconut water, and its branded entries for plain packaged coconut water show only 8-42 mg of sodium per 100 g. A liter of the packaged kind delivers 1-2 g of potassium against the 80-310 mg per liter you sweat out, while replacing a fraction of the sodium. Fine after a normal session; not the fix for a big, salty sweat, nor a free choice if your doctor limits your potassium.

Broth, salty food and pickle juice

Food is the simplest sodium source. A cup of ready-to-serve chicken broth has about 925 mg, and a quarter teaspoon of table salt about 575 mg, since the FDA puts a full teaspoon at about 2,300 mg. A salted dinner does the same job as an electrolyte powder.

Pickle juice carries sodium too, but its reputation is about cramps. In a 2010 study, about 74 ml ended electrically induced foot cramps 49 seconds sooner than water while barely changing blood composition, and the authors credited a reflex from the mouth and throat rather than rehydration.

How Much to Drink After a Session

Drink about 1.5 liters for every kilogram lost, over the next one to two hours, with some sodium if the loss was large. The ACSM position stand says people who need rapid and complete recovery from dehydration can drink about 1.5 L of fluid for each kilogram of body weight lost.

The extra covers what goes straight to the bladder. Shirreffs and colleagues dehydrated men by 2% of body weight on a bike, then gave them drinks equal to 50-200% of the loss. Matching the loss did not restore balance, and extra volume helped only when the drink carried enough sodium (61 mmol/L); with a weak drink (23 mmol/L), much of it came out as urine. Water with a salty meal or a mug of broth beats a big plain-water chug.

No scale? The NHS lists dark yellow, strong-smelling pee and peeing less often than usual as signs of dehydration, so once your urine is pale again you have most likely caught up. If you are in no hurry, normal meals and drinks through the evening restore a moderate deficit; the ACSM notes that how fast you need to recover and how big the deficit is decide whether aggressive replacement is needed at all.

When plain water is enough

As a working rule: a single session at normal settings, a scale loss under about 0.7 kg (1% of body weight at 70 kg), and a regular meal within a few hours. That covers most home sauna use.

When electrolytes actually matter

• +Big losses. The scale shows 1 kg or more, or over about 1.5% of body weight.
• +Rounds and doubles. Several rounds in an evening or two sessions in a day. Weigh after the last one.
• +After a hard workout. Losses stack, and a 1988 Finnish review of sauna and body fluid balance advises that after heavy physical activity, fluid replacement may be needed before the sauna.
• +Salty sweaters. At 80 mmol/L, a 1 L session costs over 1,800 mg of sodium.
• +Hot days. The NHS lists hot environments and sweating after exercise among common causes of dehydration.
• +Low-sodium eating. The FDA estimates that over 70% of dietary sodium comes from packaged and prepared foods, so cooking from scratch or cutting out bread leaves less buffer. If a low-salt diet is medical advice, ask before adding salt.
• +Older adults. Baker notes lower sweat output per gland with age, so young-volunteer numbers may not fit. Weigh in and out rather than going by feel.
• +Diuretics. They already increase fluid loss, and the NHS lists them as a cause of dehydration. Ask your doctor before adding salt or potassium.

If you pair sauna with training, our guide to using an infrared sauna before or after a workout covers the order and timing. Readers over 60 should also see infrared sauna for seniors for the medicines that change heat tolerance.

Can You Drink Too Much Water After a Sauna?

Yes, but only by drinking far more than you sweated, usually over hours. The result is hyponatremia, low blood sodium from diluting the body's sodium with water. In a 2002 Boston Marathon cohort reported in the New England Journal of Medicine, 13% of runners tested at the finish had it and 0.6% had a critical level. It was linked to gaining weight during the race, drinking more than 3 liters, and taking longer than four hours to finish.

A sauna session is far shorter, so the risk in normal use is low, but the pattern to avoid is the same: liters of plain water to flush out toxins, or forcing fluid down long after you have caught up. If you weigh more after rehydrating than you did before the session, you overshot. Taking sodium with the fluid makes rehydration both more effective and safer.

What to Drink Before and During a Session

Start hydrated and, for anything longer than about 30 minutes, sip during the session. The ACSM advises starting any prehydration at least several hours ahead so the fluid is absorbed and urine output settles. In practice, drink normally through the day and have a glass or two of water in the hour or two before, rather than a liter at the door.

The 1988 Finnish review called small amounts of fluid repeated frequently during bathing the most convenient and effective way to replace losses. The Cardiff participants, who drank nothing, lost 1.0 kg in 45 minutes, so a bottle on the bench keeps the deficit smaller.

Coffee before a sauna

Moderate coffee will not dehydrate you. In a three-day crossover trial, 50 habitual coffee drinkers had four 200 ml cups a day or the same volume of water, and no hydration measure differed, including total body water. The beverage index trial found the same for a liter of coffee. The caveats: the men were used to caffeine, one author worked for PepsiCo (disclosed in the paper), and the NHS still advises avoiding caffeine when you are already dehydrated.

Alcohol

Keep alcohol out of the sauna. The problem is not mainly fluid, since in the beverage index trial a liter of lager produced no more urine than water. It is what alcohol does to your circulation in the heat, and our guide to infrared sauna and alcohol covers the evidence and how long to wait.

Signs You Are Under-Hydrated After a Session

Headache, dizziness on standing, unusual tiredness, a dry mouth and dark yellow urine are the common signs, and all are on the NHS list of dehydration symptoms. After a sauna they usually combine fluid loss with a temporary drop in blood pressure: in the Cardiff study, mean arterial pressure was 9 mmHg lower right after the session and plasma volume was down 11.6%.

Sit for a few minutes before standing, drink, and eat something salty after a long session. If symptoms ease with fluid and food, you under-drank: drink more next time, shorten the session or lower the heat. Our overview of infrared sauna side effects covers overheating and the other risks that can look similar.

Who should ask a doctor first

• !Kidney disease. Fluid and electrolyte targets are individual, and extra potassium or salt is not automatically safe.
• !Heart failure or any fluid limit. Your doctor's daily limit takes priority over the 1.5 L per kg rule.
• !Blood pressure medicines. A review of sauna health effects found medication in general was of no concern during a bath, except antihypertensives, which may predispose to orthostatic hypotension (a drop in blood pressure on standing) after bathing.
• !Diuretics or a sodium-restricted diet. The broth and salty-food advice needs your doctor's sign-off.

A Practical Drinking Protocol by Session Type

Use this as a starting point, then adjust it with your own scale numbers after two or three sessions. Loss ranges come from the studies above.

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