Most sauna guides say "drink plenty of water." That's not wrong, but it's incomplete — and for frequent sauna users, incomplete hydration advice can actually cause problems.
Here's the full picture on what your body loses in an infrared sauna session, why plain water isn't always enough, and how to build an electrolyte protocol that keeps you performing at your best.
What You Actually Lose in a Sauna Session
Sweat is not just water. It contains:
| Electrolyte | Concentration in Sweat | Role in the Body |
|---|---|---|
| Sodium | 40–60 mEq/L (highest) | Fluid balance, nerve conduction, muscle contraction |
| Potassium | 5–15 mEq/L | Heart rhythm, muscle function, nerve signals |
| Magnesium | 1–5 mEq/L | 300+ enzymatic reactions, muscle relaxation, sleep |
| Calcium | 0.5–2 mEq/L | Muscle contraction, bone health, nerve function |
| Chloride | 40–60 mEq/L | Fluid balance, pH regulation |
| Zinc | Trace amounts | Immune function, wound healing, testosterone |
A typical infrared sauna session (20–30 minutes at 130°F) can produce 500mL–1.5L of sweat, depending on individual sweat rate and temperature tolerance.
That's not just water. Replacing only water after significant sweat loss dilutes remaining electrolytes — a condition called hyponatremia (low sodium). Hyponatremia can cause:
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Headaches
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Nausea
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Dizziness
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Fatigue and "brain fog"
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In severe cases: seizures and cardiac arrhythmia
Frequent sauna users who drink a lot of plain water without electrolyte replacement are at real risk of chronic hyponatremia — and often attribute the symptoms to other causes.
The Sodium Story: Most Important and Most Misunderstood
Sodium is the dominant electrolyte in sweat. It's also the most misunderstood, particularly in an era of sodium-phobia.
Sodium is not the enemy. For active people and frequent sauna users, adequate sodium is critical for:
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Maintaining plasma volume
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Enabling muscle contractions
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Supporting nerve signal transmission
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Helping the gut absorb glucose and water
Sodium also drives thirst — when you're adequately sodium-replenished, your thirst response works correctly. When sodium is depleted, you can drink liters of plain water and still not adequately hydrate (because the water dilutes rather than restores electrolyte balance).
Target: ~500–1000mg sodium replacement per liter of sweat. For a typical 30-minute sauna session, this is roughly 300–700mg total sodium.
The Magnesium Story: Underappreciated and Underconsumed
Magnesium is the second-most important sauna electrolyte and the most commonly deficient mineral in the Western diet (estimates suggest 50–70% of Americans don't meet the RDA).
Magnesium matters for sauna users specifically because:
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Muscle relaxation — one of the primary benefits of infrared sauna; magnesium is required for muscle fiber relaxation after contraction
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Sleep — magnesium is directly involved in GABA synthesis and melatonin regulation; low magnesium impairs the sleep quality you're counting on sauna to improve
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Stress response — magnesium is rapidly depleted by cortisol; if your sauna practice is partly about stress reduction, magnesium ensures the stress response doesn't perpetuate itself
Target: 200–400mg magnesium per day total (not per session). Supplemental magnesium glycinate or malate is well-absorbed; oxide is poorly absorbed and mainly acts as a laxative.
Transdermal magnesium (Epsom salt foot soaks, magnesium oil) is less well-studied but some sauna users apply magnesium oil post-session.
Complete Hydration Protocol
Pre-Session (30–60 Minutes Before)
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16–24oz water with electrolytes
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Target: 300–500mg sodium, 200mg potassium, 100mg magnesium
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Options: LMNT, Nuun, Liquid IV, or a pinch of quality sea salt in water with a squeeze of citrus
Do not: Drink a large volume of plain water immediately before sauna — it dilutes sodium and can impair thermoregulation.
During Session
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Keep a water bottle accessible (not cold — room temperature or warm is fine)
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Sip small amounts if thirsty — 4–8oz per 10 minutes of session is reasonable
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Don't force fluids if not thirsty — you can over-hydrate during session
Post-Session (Within 30 Minutes)
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Weigh yourself before and after — every pound lost = approximately 16oz of fluid loss
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Replace fluid losses 1:1 to 1.5:1 (replace each pound lost with 16–24oz)
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Include electrolytes in post-session fluid — not plain water alone
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Target: 500–700mg sodium, 300mg potassium, 200mg magnesium in post-session replenishment
Best Electrolyte Sources
Commercial products:
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LMNT — high sodium (1000mg/packet), zero sugar, excellent for serious sauna users
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Liquid IV — lower sodium but includes glucose (helps with absorption)
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Nuun — lower sodium, tablet format, convenient
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Pedialyte — clinically formulated, good for aggressive rehydration
Food sources:
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Dill pickles / pickle juice — surprisingly effective sodium source
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Bone broth — sodium + minerals + glycine (which also aids sleep and gut health)
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Bananas — good potassium
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Coconut water — potassium + some sodium, naturally occurring
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Salted nuts — sodium + magnesium
DIY electrolyte drink: Mix in 16oz water:
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¼ tsp sea salt (≈600mg sodium)
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¼ tsp potassium chloride (No Salt brand, ≈700mg potassium)
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Juice of ½ lemon (vitamin C + flavor)
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Optional: pinch of magnesium glycinate powder
Cost: pennies per serving, fully customizable. how much does an infrared sauna cost
Special Populations: Modified Protocols
Athletes Training Hard
Athletes using sauna for heat adaptation or recovery have higher sweat rates and often back sauna sessions onto existing training losses. Doubles the electrolyte demand.
Recommended: LMNT (1000mg sodium) pre-session + 1000mg sodium post-session. Magnesium supplementation daily.
Older Adults (65+)
Thirst response diminishes with age. Older adults are at higher risk of dehydration without feeling thirsty. Scheduled fluid intake (not relying on thirst) is important.
Set a timer for a pre-session fluid protocol; don't rely on thirst as the signal.
Ketogenic/Carnivore Dieters
Low-carbohydrate diets reduce insulin, which reduces sodium retention by the kidneys. Keto dieters lose more sodium than standard dieters — even without sauna. Sauna compounds this. LMNT was specifically formulated with this population in mind (1000mg sodium per packet).
Those on Medications
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Diuretics (hydrochlorothiazide, furosemide): already increase electrolyte loss — sauna compounds this significantly. Consult physician.
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ACE inhibitors / ARBs: affect fluid/electrolyte balance. Monitor blood pressure response.
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NSAIDs: regular use reduces kidney sodium excretion, which can interact with sauna-induced losses unpredictably.
Signs You're Under-Hydrating or Imbalanced
Watch for these signals:
Sodium depletion: Headache, muscle cramps, nausea, dizziness, fatigue despite adequate water intake Potassium depletion: Muscle weakness, heart palpitations, constipation Magnesium depletion: Muscle twitches, poor sleep, anxiety, calf cramps at night General dehydration: Dark yellow/amber urine, persistent fatigue, headache, reduced sweating in subsequent sessions
Peak Saunas and the Hydration Practice
Building a sustainable sauna practice means building the hydration habits that make every session safe and effective. Peak Saunas' full-spectrum infrared delivers more sweat and deeper benefits — which is exactly what you want, paired with proper electrolyte protocol.
Limited lifetime warranty. Free shipping. Built for daily use, because that's where the real results accumulate.
Explore Peak Saunas — and treat your hydration as seriously as your heat practice.