*Disclaimer: The written article is based on a summary of existing literature on the topic of infrared saunas. The article is for educational purposes and the information provided below cannot be taken as a promise to help with acute health problems or diseases.
The claims in the article are backed by 23 scientific references. All references are numbered. You can access the text of the reference by clicking on the number.
Once in a while, but very infrequently, I'm asked the question: "Johannes, I've got diarrhoea after infrared sauna use! How is this possible?!" This blog post explores the science of several different potential answers to the diarrhoea after sauna link.
I hope you're not eating or drinking right now because we'll be covering a topic that affects people on a visceral level:
What Is "Diarrhoea", "Dysentery", Or "The Runs"
With the "runs" everyone knows what I mean but tackle the issue from a more scientific definition:
If you have diarrhoea or "the runs", your stools have become very loose and are paired with tons of water. That problem originates because either your bowels don't absorb much water anymore or they expel too much of it. Diarrhoea is a sign that your bowel movements have been impaired and that food isn't properly digested.
Diarrhoea can have many different causes, types, and solutions - so there's no one monolithic phenomenon called "diarrhoea" (1; 2; 3). And while the condition seems harmless to many people in the developed world, diarrhoea still causes 200,000 deaths every year on a worldwide basis.
Let me explain:
Acute diarrhoea isn't dangerous in most cases. In the long-term, however, diarrhoea can cause a mineral loss in the human body and even eventually the dreaded death. In this blog post, I'll be talking about the occasional acute diarrhoea that people may have after an infrared sauna session.
Food intolerances, viruses and bacteria, poor hygienic conditions, improper gut microbiome makeup, and parasites are some of the main causes of acute diarrhoea. So how then can an infrared sauna give you diarrhoea? Several mechanisms exist, in fact - let's explore four of them:
Reason 1: High Levels Of Stress Hormones
Several studies have actually explored the effects of saunas on your hormone levels.
For instance, the "cortisol" hormone that's responsible for increasing the body's breakdown of tissues doesn't seem to increase with sauna use - although studies are contradictory (4; 5; 6). Adrenaline and noradrenaline, however, which are both stress hormones, can more than double though and stay elevated after a session (7; 8; 9).
And, even though I cannot find any research directly linking these neurotransmitters to diarrhoea, stress, in general, does increase diarrhoea risk (10; 11; 12; 13).
So here's why that dynamic matters:
Drugs that directly increase stress hormones such as adrenaline (epinephrine) also have acute diarrhoea as a common side-effect (14; 15).
If you're not used to sauna sessions then they can be very stressful to the body, especially if you stay in too long. A similar concept would be when you're starting to exercise after years of doing nothing - your body is simply not used to the stimulus and might feel very stressed initially.
Hence, your sessions might be so intense because you've not gotten used to the stimulus that your body pumps out tons of stress hormones. These stress hormones can cause diarrhoea, in turn.
Acute diarrhoea is harmless here, but, inconvenient, of course.
But, stress is not the only reason. Let's consider another reason as to why can infrared saunas give you diarrhoea, potentially:
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Reason 2: A Strong Detoxification Response
There is ample proof that human beings detoxify through their skins (16; 17; 18). Popular online sources such as newspapers are usually not aware of that fact.
Detoxification can be hard on the body though, as chemicals from household products or heavy metals are removed from your cells and released into the bloodstream. If the body cannot easily get rid of those toxins, they may do more harm than good even. For that reason, detoxification should never be the first step in any healing process - you generally have to build up overall health first before detoxing.
The body has several methods of getting rid of toxins, which not only includes sweat but also your breath, your stools, and more. Before toxins are removed from your body they often travel an extensive journey through you. And, because detoxification increases rather than decreases stress on the body, it can be paired with increased symptoms.
Of course, infrared saunas are a primary way through which you can increase detoxification in your body. And, with increased detoxification symptoms can appear, such as headaches, fatigue, low energy, feeling jittery, and, you guessed it: diarrhoea.
If you do get diarrhoea consistently after sauna sessions, try cutting down on the length or intensity of your sessions and observe how your body responds. Also, make sure to eat well throughout the day - including some fibre to help your digestive system remove toxins - and drink enough water for proper sweating.
If the diarrhoea sauna connection keeps coming up, then I'd recommend visiting a doctor because you might have an underlying health issue. Saunas shouldn't consistently cause diarrhoea over time!
Next up, there's another reason why you can get the runs:
Reason 3: A Feverish Response
Saunas, including infrared saunas, really heat up your core body temperature. The effect of sitting inside a sauna is akin to artificially creating a fever within your body.
If you heat up your body temperature to an extreme level, then infrared saunas can give you diarrhoea for sure. To find out why let's look at some of the research on fevers:
In studies using extreme heat - simulated with "whole body hyperthermia" - diarrhoea is actually a frequent side effect (19; 20; 21; 22). These studies are great because participants in them are usually heated towards what is commonly understood as a fever for a long period of time, up to several hours.
Vomiting and nausea are similar side-effects.
So here's what I'm trying to say: as a result of heating up your body, diarrhoea might be an infrared sauna side-effect. That side-effect is especially likely to occur if you don't have good heat tolerance.
Now, usually, most people won't raise their body temperature nearly as much with sauna sessions as they would with whole body hyperthermia sessions. And yet, individuals are different from each other with slightly different biological makeups.
Hence, even though diarrhoea might be decently uncommon as a side-effect of saunas, you might be an individual who is more susceptible to that side-effect.
Reason 4: Dehydration
This reason is somewhat counterintuitive, but, in severe dehydration, some people will develop diarrhoea. A study even recently directly investigated this phenomenon and concluded that inside your intestinal system, sauna sessions where you lose 3% or more of your body weight can increase the permeability of that system (23).
Of course, the causal connection between dehydration and diarrhoea is usually explained the other way around: once you end up with diarrhoea, you're far more likely to end up dehydrated because you're now losing water from one additional place in your body. And, of course, that connection absolutely exists.
But, now it seems that dehydration itself caused by heating can also increase the risk of diarrhoea in some instances. Fortunately, this issue can easily be countered once again by drinking enough water during your sauna sessions.
And, losing 3% bodyweight usually is several pounds, so for this effect to happen, you'll really have to go crazy on your sauna sessions.
Let's now conclude:
Can Saunas Give You Diarrhoea? Yes. Should You Worry? Generally Not!
So, let's zoom out and consider the bigger picture.
Overall, diarrhoea is thus very unlikely to happen and usually a sign you're going too hard during your sauna sessions, whether it's due to stress hormones, detoxification, an intentionally created fever, or extreme dehydration. In all cases, you're overexerting yourself
Also, for only a few per cent of people, the sauna causes diarrhoea problem is really relevant. For 95%+ of people, diarrhoea and saunas are a non-issue because it's acute and will pass.
And yet, you might be worried whether what you're feeling is normal. For that reason, I've given you several reasons why people might commonly experience this unfortunate side-effect.
The solution is also very simple: go easier on your sessions to lower the detoxification and fever response. Also make sure that you're drinking enough high-quality water and eating sufficient levels of food to support proper detoxification. Lastly, make sure to build up your heat tolerance over time. Rome wasn't built in a day - heat tolerance can't be either!