What an infrared sauna blanket does to your body

An infrared blanket does not warm you by heating the air around you. The heating elements give off far infrared radiation. That radiation hits your clothing or skin and only becomes heat there. That is the whole mechanism: no hot air against you, but energy that turns into heat where it lands.

Far infrared does not penetrate far. It concerns the top few tenths of a millimetre of your skin and the tissue just below it. Stories about heat going centimetres deep into your muscles are not accurate. Still, after a while the heat feels deeper, and there is a simple explanation for that.

Your skin contains a dense network of small blood vessels. As soon as the skin warms up, those vessels widen and more blood flows through them. That blood takes heat with it, returns to your torso and releases it there. This way, heat that started at the surface moves through your whole body within a few minutes.

This also explains why people whose hands and feet get cold easily only feel them warm up late in the session: that is where the warmed blood arrives last. How the radiation itself works is explained in how infrared heat works.

Your body keeps its core temperature within a narrow margin around 37 °C, because organs and enzymes only work well within it. When heat is added from outside, a control system kicks in that tries to get rid of it again. Almost everything you feel during a session is that system at work.

Your brain receives signals from heat sensors in the skin and from the blood flowing past. Based on that, it starts two things: sending more blood to the skin and switching on the sweat glands. In a closed blanket the first only works halfway, because the blanket holds heat in. So the emphasis shifts to sweating early on.

In a traditional sauna you breathe in air of 80 °C or more. Your face and airways take the full heat, and for many people that is the stuffy part. In a blanket your head stays outside and you breathe room air. Your body warms up while your breathing stays cool.

The heat load on your body can be similar, but the signals your brain receives are different. People who quickly find a sauna cabin too much often last longer in a blanket. That comparison is worked out further in a sauna blanket and a traditional sauna side by side.

Sweating is the strongest cooling mechanism you have. It is not the sweat itself that cools, but its evaporation: that takes energy, which is drawn from your skin. In a closed blanket the air around you quickly becomes saturated with moisture, so less evaporates. As a result you tend to sweat more rather than less, while the cooling falls short.

When sweating starts varies a lot. For one person it is on their chest after eight minutes, for another little happens in the first half hour. That says nothing about your fitness, but about your sweat glands, how used you are to heat and what you drank that day.

What you see on the scales after a session is almost entirely fluid. Half a kilo less means exactly one thing: you have lost half a litre of fluid, and as soon as you drink it is back.

If you hardly get sweating at all, the urge to turn the setting right up is understandable but not wise. The causes are covered in not being able to sweat in the sauna.

As soon as the blood vessels in your skin open up, something changes in your circulation. There is more room in the system while the amount of blood stays the same, so your heart beats more often. In a calm session your heart rate gradually rises to a level many people compare to an easy walk. You are lying still, but your heart is working harder than at rest.

Important to know: this is not a workout. Your muscles do nothing and you do not build fitness with it. The higher heart rate is a reaction to heat, nothing more. Comparisons with running miss that point.

Your breathing usually becomes a little calmer and deeper. That is not so much due to the heat as to the situation: lying down, few distractions, nothing to do. In people who get too warm, breathing becomes fast and shallow instead. That is the moment to turn the setting down.

Your blood pressure often drops slightly in the heat, because the blood vessels are wider. You only notice it when you stand up: you may feel lightheaded for a moment. Get up slowly and sit for a while first.

For most people the course is fairly predictable, even if the moments vary. The order below assumes a session of about 35 minutes on a medium setting.

What happens after the session shapes the experience at least as much as the session itself. Your body has stored heat and needs some time to get rid of it. In that hour most people feel warm first, then drowsy and then calm.

The drop in temperature afterwards plays a part in that. After warming up, your body temperature falls to a level that can be slightly below where you started. Your body goes through that same drop on the way to sleep. That is the most likely explanation for the sleepy feeling after an evening session.

Cool down gradually instead of jumping straight into a cold shower. A lukewarm shower rinses off the sweat without shocking your system. Drink water and keep in mind that you have also lost salt. Keep the hour afterwards as free as possible.

If you are wide awake after an evening session, it is usually the timing. Shortly before bed you are still in the middle of the phase in which your body releases heat, and that works against falling asleep. More on that in the piece about sauna before bed and why you are sometimes wide awake.

Two people using the same blanket on the same setting can have a completely different session. That is normal and says nothing about the device.

Honesty belongs here. There is a fair amount of research on heat and sauna use, mostly in cabins or a clinical setting. There is hardly any research specifically on infrared sauna blankets for home use. That does not mean a blanket does nothing, but it does mean you cannot simply transfer sauna research to it.

What you find online about calorie burning, detox or long term effects is largely unsupported for this product. What is established is more limited: heat increases blood flow in the skin, starts sweating, raises the heart rate and temporarily raises the temperature of the tissue. What people get out of it in practice is relaxation and a regular moment of rest. More on this in infrared sauna and research.