Short answer: an infrared sauna won't melt fat on its own. The pounds you drop in a session are mostly sweat, and they come back when you drink. Your body does burn a few extra calories to cope with the heat, but the amount is modest. Where a sauna can genuinely help is the stuff around weight loss: a relaxing habit, a pleasant cool-down after workouts, and possibly better sleep. Diet and regular exercise still do the heavy lifting.
Below we break down what actually happens in an infrared sauna, what the research does and doesn't show, and how to use one safely alongside a weight-loss plan.
What happens to your body in an infrared sauna
Unlike a traditional sauna that heats the air to a high temperature, an infrared sauna uses infrared heaters to warm your body more directly at a lower air temperature (see infrared vs traditional saunas). Either way, your skin and core temperature rise, your heart beats faster to move blood to the skin, and you sweat to cool down.
| What you notice | What's really going on | Does it mean fat loss? |
|---|---|---|
| Lower number on the scale after a session | Fluid lost as sweat | No. It returns once you rehydrate. |
| Faster heart rate | Your heart pumps blood to the skin to shed heat | Only a small extra calorie burn, not a workout |
| Feeling relaxed or sleepy afterwards | Warmth and quiet time; many people find it calming | Indirectly at most, if it helps your sleep and routine |
Water weight vs fat loss
Sweat is the most obvious effect, and it's common to weigh less straight after a session. In one study, 45 young overweight men who sat through four 10-minute rounds in a hot Finnish sauna lost about 0.65 kg (roughly 1.4 lb) of body mass, almost all of it fluid (Podstawski et al., 2019).
That drop is not fat. It comes back as soon as you drink, and you should drink: trying to sweat off weight by dehydrating yourself is risky. Real fat loss happens when you use more energy than you take in over weeks and months.
How many calories does an infrared sauna burn?
Less than the internet suggests, and nobody has measured it well for infrared saunas. The best figures we found come from that same Finnish sauna study, where heart-rate monitors estimated about 73 calories in the first 10-minute round, rising to about 131 calories in the fourth. Two things to keep in mind:
- Those men sat in a sauna at about 90°C (194°F). Infrared saunas usually run far cooler, around 120-140°F, so the extra burn is likely smaller.
- The monitors estimate calories from heart rate, and heat raises your heart rate on its own. Treat these numbers as rough upper estimates, not a reason to skip a walk.
Claims of 300 to 600 calories per session aren't backed by good current research. A sauna session is a small extra, not a substitute for exercise.
Where a sauna can support a weight-loss plan
A comfortable cool-down after training
Consistency is what makes exercise work, and anything that makes your routine more enjoyable helps you stick with it. The evidence on recovery itself is limited. A small Finnish study of 10 active men found far-infrared sauna bathing made no difference to recovery after strength training, and gave slightly better jump height 30 minutes after a hard endurance session (Mero et al., 2015, SpringerPlus). The researchers described it as light on the body and comfortable. For timing tips, see sauna before or after a workout.
Relaxation and sleep
Many people find a warm session a good way to wind down in the evening. That matters because short sleep is linked to changes in the appetite hormones ghrelin and leptin and to weight gain (review: sleep and obesity). A sauna isn't a sleep treatment, but if it helps you relax and get to bed on time, that supports the habits that drive weight loss.
How to use an infrared sauna alongside a weight-loss plan
- Drink water before and after. Have a glass or two of water beforehand, keep a bottle with you, and rehydrate afterwards. After a long sweat, some people add electrolytes. Skip alcohol before and during a session.
- Start cool and short. Many people use about 120-140°F in an infrared sauna. Begin with 10-15 minutes and add time only if you feel comfortable, following your sauna's manual. Our sauna temperature guide covers the ranges in more detail.
- Go after your workout, not before. Heat before training can leave you tired and dehydrated. After exercise, let your heart rate settle for a few minutes first.
- Keep it regular, not extreme. Two to four sessions a week is a common, comfortable rhythm. Longer or hotter sessions don't add meaningful fat loss and raise the risk of dehydration and dizziness. See how long to stay in a sauna for safe session times.
- Judge progress over weeks. Weigh yourself at the same time of day, before a sauna session, not straight after one.
Who should check with a doctor first
For most healthy adults, sauna use is well tolerated. Heat does put extra demand on your heart and circulation, so talk to your doctor first if any of these apply:
- Heart conditions: people with unstable angina, a recent heart attack or severe aortic stenosis are advised to avoid saunas (Hannuksela and Ellahham, Am J Med 2001).
- Pregnancy: the American College of Obstetricians and Gynecologists advises avoiding overheating, especially in the first trimester, and lists hot yoga and hot Pilates among activities to avoid. Ask your provider before using a sauna.
- Low blood pressure or a history of fainting: heat can lower blood pressure further.
- Kidney disease or any condition where you've been told to limit fluids.
- Medications that affect sweating, blood pressure or hydration, such as diuretics.
Leave the sauna straight away if you feel dizzy, nauseous or unwell.
The bottom line
Can you lose weight with an infrared sauna? Not in the way the "burn 600 calories sitting down" posts promise. You'll lose water that comes straight back, and burn a modest number of extra calories. If you enjoy it, a sauna can be a pleasant, relaxing part of a routine built on eating well, moving more and sleeping enough. If you're shopping for one, start with what size sauna you need, and read our honest look at infrared sauna benefits for what the research supports beyond weight.
