Hot Baths for Injury & Pain
Tips for getting the most benefit from a hot soak, the oldest form of therapy
I am sure there are things that can’t be cured by a good bath but I can’t think of one.
Sylvia Plath, The Bell Jar
A hot bath is the original hydrotherapy — water treatment — and still the best. Immersion, buoyancy, heat, and vibration (if you’ve got jets) all have useful biological and sensory effects, many of which are useful to people with injuries, pain, anxiety, depression, and more.1
But as much as you may already enjoy a nice hot bath, you may not be tapping its full therapeutic potential. To get the most benefit out of a hot soak, here are several tips and tricks.
Don’t make it crazy hot
A hot bath is liquid psychotherapy. It is peaceful and soothing. Chances are, once you’ve started a bath, you feel insulated from your troubles — you know you’ll have to pay attention to them soon enough, but not just now.
But superheated baths actually get your nervous system revved up, and the relaxation is a bit of an illusion. The ritual, though, is safe and soothing. The heat dominates your awareness and forces out other thoughts. You’re sluggish while your body temperature drifts back to normal, and you recover from the wet-noodle exhaustion. It is a type of relaxation.
But you’re also on fire neurologically, and out of whack homeostatically. Your system is turbulent, like boiling water. Many people cannot sleep well after a piping hot bath. It’s a particularly bad idea for insomniacs to have hot baths late in the evening.
The most relaxing baths are not quite piping hot. If you are bathing for sedation or specifically to help you sleep, keep the temperature “easy.”
Of course, “some like it hot” …
Get a thermal workout, and consider alternating with cool
They don’t call it “heat exhaustion” for nothing: enduring intense heat can be tiring. Your circulatory system has to do a lot of work to cope with high temperatures. You sweat a lot, and you can actually burn some calories.
This is a “thermal workout,” and it can be a nice way of wearing yourself out — but it’s better to do it earlier enough in the day that your nervous system can calm down before bed time (probably a couple hours leeway at least). Also, make sure that it’s not actually dehydration that’s making you feel whipped afterwards: drink extra water before and after.
If you alternate between a hot bath and a cool shower or pool, things get even more exhausting — and even a bit dangerous, so please be careful and don’t overdo it, especially if you’re not fit or have any kind of heart trouble.
Contrast Hydrotherapy — “Exercising” tissues with quick changes in temperature, to help with pain and injury rehab (especially repetitive strain injuries). (3,500 words, 15-min read)
Vintage “electric bath”
Do NOT add electricity to your bath! This is an example of a bath that is not better. Source: olden times.
Keep a cool head
Many people avoid hot baths because they feel wilted and cruddy afterwards. Some people get post-bath headaches. This can usually be avoided by keeping a cool head. Or feet. Or hands. Or all three. Your head, feet, and hands are good “radiators” — places where the body can get rid of heat.2
As beneficial as heat can be, your body doesn’t really love being heated up entirely, with no opportunity at all for heat shedding. This creates an artificial fever. An artificial fever has its uses (more below), but it can also have some unpleasant side effects, such as headaches.
So while you’re enjoying your hot bath, pour glasses of cool water over yourself! Or drape a cool washcloth over your neck. Or spray your feet with a shower hose.
Give your body some opportunity to shed some heat. Your core body temperature will still go up (and you’ll get the benefits of that), but it will cause less physiological stress. You may be quite surprised at how much this improves your experience.
Combine a hot bath with self-massage
A bath is a great place to do a little self-massage. And the perfect method: bring a ball into the bath with you and trap it under your body to apply pressure to stiff and aching muscles. I call this “the bath trick,” because it’s such a nice combination of therapeutic factors. The bath trick works particularly well because the pressure you apply to your muscles is easy to control.
The Bath Trick
Run a hot bath & trap a ball between your body & the bottom or back of the tub to rub your back muscles — your buoyancy allows for excellent control over moderate pressures.
In standard “tennis ball massage,” often people find that the full weight of their body trapping a tennis ball against the floor is simply too much — the pressure is too intense, and they’re unable to achieve a relieving sensation. But in the bath, you are much lighter! You have much better control and a moderate intensity of pressure.
While the heat relaxes you, your buoyancy in the water allows finely tuned control over moderate pressure on your stiff and aching muscles. Applying a little more or less pressure is as simple as rising up in the water a little, or submerging more of yourself.
The Bath Trick for Trigger Point Release — A clever way of combining self-treatment techniques to self-treat your trigger points (muscle knots). (850 words, 4-min read)
Basic Self-Massage Tips for Myofascial Trigger Points — Learn how to massage your own trigger points (muscle knots). (2,750 words, 11-min read)
Combine a hot bath with stretch
Stretching is not as therapeutically useful as most people imagine,3 but it certainly can feel great, and it’s probably not entirely useless. Stretching might be modestly effective for relieving muscular aches and pains, possibly because it meaningfully changes tissue, but more likely because it’s a pleasant sensory input, like scratching an “itch.”4 It’s not exactly guaranteed to work miracles — lots of people fail to treat this kind of pain just by stretching. But doing it in a hot bath probably improves your odds, for a variety of possible reasons:
- Baseline muscle tone drops when you’re happy and warm.
- The bath softens connective tissue through “thixotropic” effect, very much like softening plastic with heat.5
- It might ease the (hypothetical) neurological vicious cycle that powers “trigger points.” More on this topic below.
- Extensive evidence suggests that increases in flexibility from stretching are the result of reduction of inhibition, not a change in the physical condition of tissue. But the heat of the bath is probably helpful either way.
- The buoyancy of the bath makes some stretches physically easier and more relaxing. (Others are more awkward. You win some, you lose some.)
If you’re going to stretch, then stretch in the bath. (Or a pool!)
Quite a Stretch — Stretching science has shown that this extremely popular form of exercise has almost no measurable benefits. (34,000 words, 139-min read)
Winnie-the-Pooh. This is an illustration from the original 1926 book, which finally entered the public domain in 2022.
Almost always choose a hot bath for low back pain
A hot bath is not only a better choice for most low back pain than icing — which might even be a little harmful — but soaking in the tub may simply be the single best therapy there is for low back pain, or at least the best bang for your buck. Or 30 cents, which is roughly what it cost to fill a bath.
And yet many people actually avoid a hot bath when they have low back pain — tragically — because they think they are “inflamed” and the heat will make it worse. This is probably rarely the case. In many cases, there’s probably little or no inflammation at all (or, even if there is, it’s simply too deep to be significantly aggravated by the heat). Back pain is extremely complex, but as a general rule its bark is worse than it’s bite: it involves much less damaged, fragile, and “degenerated” spinal tissue that people fear.
In some cases, much of the pain could be coming from relatively innocuous muscle discomfort — painful and disabling, but not fragile or serious. For poorly understood reasons, muscle can become extremely sensitive in well-defined spots, with a lot of associated aching and stiffness. These are what are popularly called “muscle knots” or “trigger points,” a controversial but interesting idea, covered extensively in other articles on PainScience.com.6
In some cases, these sore spots can get so severe that may overshadow other factors, or perhaps even be the entire problem. And here’s the thing: they definitely seem to be soothed by heat. While there is no proven therapy for this kind of discomfort, a little rubbing and hot soaking often seem to be surprisingly effective. A hot bath can be amazingly good therapy for back pain … and the price sure is right.
And this kind of pain also seems to be irritated by cold. For more information about why you shouldn’t ice low back pain, see (Almost) Never Use Ice on Low Back Pain!. For (much) more information about the nature of low back pain, see:
The Complete Guide to Low Back Pain — An extremely detailed guide to the myths, controversies, and treatment options for low back pain. (187,500 words, 760-min read)
A hot success story!
Heat rarely works miracles on muscle pain. Fortunately, “rarely” is not “never.” I once awoke from a poor sleep in an unfamiliar bed with an extremely unpleasant new pain halfway along the length of my spine, and just to the left of it. It had all the classic signs of being a fresh trigger point (muscle knot) in my erector spinae muscle group: a deep spreading ache with a vivid epicentre, painful resistance to stretch, and a nagging craving for focused pressure. I was travelling home that morning, and the pain made me grouchy every minute of the trip. Hours of cars, ferries, and crowded public buses are awful when your back is howling.
Upon arrival at home, I felt about ready to try to rip a chunk of my own back out to get rid of the pain. Lacking the claws or will for such an excision, I hopped into our building jacuzzi immediately upon arrival, and applied piping hot jets of water to the spot for about 20 minutes … and that was simply the end of my ordeal: the pain was reduced about 95%, the remainder so trivial that I barely thought about it again for the rest of the day. By the next morning, it was gone entirely.
Hydrate for enhanced elimination (but not “detoxification”)
You sweat under water. In a hot bath, oddly enough, you can really lose a quite a lot of fluid.
Sweating is an important form of excretion, and some waste metabolites are removed from the body this way. Exercise is one way to do this, of course, but a hot bath is a lot easier — and, in fact, people usually sweat much more in a bath than they ever do when exercising.
Some people will call this “detoxification,” but I encourage you to stay away from that word — it gets thrown around waaaaay too casually (usually to make something sound more therapeutic than it really is).7 A good sweat is a dandy thing, but it isn’t “detoxifying” any more (or any less) than having a bowel movement. It is more sensible to simply say that sweating stimulates normal elimination of waste products.
But sweating a lot in a bath also means that you must drink water — before, during, and after! This is a vital key that most people miss. If you don’t hydrate, a hot bath can be fairly stressful. I think this is actually a major reason why some people do not like baths — they get much more dehydrated than they realize, and that’s a one-way ticket to grumpyland. A headache is the most common consequence. You must replace lost fluids to feel good after a hot bath.
Drinking a lot of water is definitely not as important as most people seem to think8, and there’s actually a genuine danger in the modern craze for constantly sucking on a bottle of water: you can drink too much.9 However, when it comes to hot baths, you definitely do need to replace lost fluids — and it’s easy to lose more than you suspect.
If I melt dry ice, can I take a bath without getting wet?
comedian Steven Wright
Baths for relief from muscle aching
Hot baths are modestly effective as a treatment for some kinds of muscle soreness. This is surprisingly hard to prove, or even understand — it’s not exactly a hot target for research funding. But it’s also pretty obvious to us all that it works, at least a little, sometimes. Here are some possible reasons why …
Covering yourself in hot water — “systemic” heating — can do something for muscles that no hot pack can ever do. As good as a nice hot pack can feel, the effect is a minor, local, neurological effect — warm skin relaxes the muscles underneath it. That’s a nice effect, but it’s limited. A hot bath also has this effect, but it goes much deeper: it can actually increase the temperature of the muscle itself via deep heating.
Hot packs simply can’t increase the heat inside your muscles. The human body is incredibly good at temperature control, at getting rid of heat. When you try to heat a muscle with a hot pack, you end up heating just the superficial blood, which quickly gets pumped away and immediately cooled.10 So what to do? How to get the benefits of heating? The hot bath may work.
In a hot enough bath, excess heat has nowhere to go. The body cannot get rid of it all (even if you’re using your “radiators”). There’s a net gain of heat, and so the entire system gets warmer — a mild fever!11 It’s not a major effect, but it’s certainly much more than you can manage with a hot pack.
And what good is a mild, artificial fever for sore muscles? Hard to be sure. Delayed onset (post-exercise) muscle soreness is notoriously difficult to treat — almost impossible really — and yet maybe hot baths help. It’s hardly proof, but one study (predictably European) of “warm underwater jet massage” was promising.12
But if hot baths help sore muscles, it’s more likely because they have some effect on those muscle knots. Like stretching, the results seem to be erratic at best — but it is free and pleasant to try. The point here is mainly that an “artificial” fever is definitely a complex and interesting biological state (and the only other ways to achieve it are icky and fun-spoiling, at best). So it’s pretty interesting to have in mind as an optional goal. When the whole system is in an altered state maybe some things change. Like pain.
Don’t bother with Epsom salts
Another common idea for bathing is that Epsom salts assist with detoxification and recovery from minor injuries, aches, and pain. Do they?
No, probably not. Some recent scientific evidence has shown that Epsom salts do indeed soak through the skin when you bathe in them13 — which is actually a bit biologically surprising, and had never been proven before. And, meanwhile, other evidence pretty strongly suggests just the opposite.14 (Science is awkward like that.)
Unfortunately, even if Epsom salts do soak through the skin, there is no direct scientific evidence whatsoever about what happens to them after that — and it’s not really plausible that they treat pain. There’s no chemistry involved that seems to have anything to do with common pain problems.
People certainly think there’s a therapeutic effect, but unfortunately that’s no way to judge the matter — people think all kinds of things,15 and in this case it would be very easy to mistake the benefits of the heat for an effect of the salt. For a surprisingly detailed discussion, see:
Does Epsom Salt Work? — The science and mythology of Epsom salt bathing for recovery from muscle pain, soreness, or injury. (22,000 words, 88-min read)
Breathe to “blow off steam”
Noble deeds and hot baths are the best cures for depression.
Dodie Smith, I Capture the Castle
After years of “therapeutic bathing,” I am still experimenting. One thing I’ve learned about bathing that I can’t really explain is that the experience is improved by strong, deep breathing. Not slow, meditative breaths — that’s what you probably expect me to recommend — but deep, strong breathing to “blow off steam.” Huffing and puffing a bit. Enough that it might call for some explaining to anyone in earshot.
I’m fascinated by the way this breathing method seems to extend my tolerance for the heat and enhance relaxation.16
Conscious, deeper breathing is always relaxing, grounding, and embodying. It can make you more comfortable in your own skin. But it seems to be particularly effective in a hot bath. For more about this kind of breathing, see:
The Art of Bioenergetic Breathing — A potent tool for personal growth and transformation by breathing quickly and deeply. (3,000 words, 12-min read)
Bath logistics: not everyone fits in a tub!
I’m 5’4" tall — the size of a hobbit — and slender, so I never have difficulty fitting into airline seats or baths, and it’s easy for me to forget that larger people often have to squeeeeze into spaces I find quite roomy. For anyone more than “medium” sized, this is another way that baths can fail to be awesome:
After a long day of roofing, a nice Epsom salt bath sounded great, as I always think a bath sounds great, in principle. In practice, I deal with legs that take up 98% of the tub, if I want to dunk my head under, those walking stalks need too be near the shower head. Leaving me with the choice of “nipples or knees” to soak in this “relaxing” environment. And of course, one must fold the shoulders so they may enter this hot soup of discomfiting comfort. Oh the pure bliss of soak therapy! Until they make a tub that can actually fit a lanky frame, or I can afford a hot tub, I am sticking to showers.
Robert Ives, artist, builder, Victoria, BC
There is usually no affordable or practical solution to this problem! But it’s a good reminder that “it depends,” and you’re not going to be able to get maximum value out of a bath if you have to pretzel yourself to get into it.
The one easy tip I have: at the least, get a bath cushion. Even a small cushion can make a surprisingly large difference in bath comfort.
About Paul Ingraham
I am a science writer in Vancouver, Canada. I was a Registered Massage Therapist for a decade and the assistant editor of ScienceBasedMedicine.org for several years. I’ve had many injuries as a runner and ultimate player, and I’ve been a chronic pain patient myself since 2015. Full bio. See you on Facebook or Twitter., or subscribe:
- Heat is straightforwardly relaxing, plus it has some strong effects on circulation. Buoyancy and vibration act as a novel sensory inputs. Immersion and flotation are particularly interesting, and are discussed in more detail in a separate article about aquatic therapy. Although regular bathtubs aren’t big enough for significant immersion effects, hot tubs are.
- This is why mittens, socks and hats are so important for preventing hypothermia in cold weather. The armpits and groin are also good radiators, but it’s harder to use them while also enjoying a hot bath.
- Ingraham. Quite a Stretch: Stretching science has shown that this extremely popular form of exercise has almost no measurable benefits. ❐ PainScience.com. 34729 words.
- When I say that it’s like scratching an itch, I mean that the effect may be entirely sensory/neurological — that there is no tangible effect on the actual condition of the tissue, but it does feel good.
- Ingraham. Thixotropy is Nifty, but It’s Not Therapy: A curious property of connective tissue is often claimed as a therapy. ❐ PainScience.com. 1010 words.
- There is a lot of scientific uncertainty about the idea of trigger points. It’s undeniable that mammals suffer from sensitive spots in our soft tissues, but their nature remains unclear, treatments dubious and often snake oily, and the popular idea that they are a kind of micro cramp could well be wrong. I’ve written extensively about this topic: Trigger Point Doubts: Do muscle knots exist? Exploring controversies about the existence and nature of so-called “trigger points” and myofascial pain syndrome.
- The idea of “toxins” is usually used as a tactic to scare people into buying de-toxifying snake oil. Exactly what substances and how they are to be removed is always vague, because the sellers are making it up. The body deals with unwanted molecules in many ways; the only truly detoxifying treatments help the body eliminate or disarm molecules the body cannot process on its own, like a stomach pump or an antivenom. Anything less, like mildly stimulating one normal excretion pathway in a sauna, is a detox scam.
- Ingraham. Water Fever and the Fear of Chronic Dehydration: Do we really need eight glasses of water per day? ❐ PainScience.com. 4575 words.
- Almond CS, Shin AY, Fortescue EB, et al. Hyponatremia among runners in the Boston Marathon. N Engl J Med. 2005 Apr;352(15):1550–6. PubMed 15829535 ❐ PainSci Bibliography 55209 ❐
According to this report, over-hydrating (hyponatremia) “has emerged as an important cause of race-related death and life-threatening illness” in marathoners. Race-related death and life-threatening illness! From drinking too much water! The researchers found that hyponatremia does occur in a “substantial fraction” of nonelite runners, and the factors most likely to be associated with it are “considerable weight gain while running, a long racing time, and body mass index extremes.”
- It has been shown that local heating never “penetrates” much deeper into the tissue than a centimetre, and probably not even that much unless the heat is intense. The only really effective way to heat a specific muscle is by making it work, to produce heat from the inside out by burning metabolic fuel. But often this is not desirable in an injured or very fatigued muscle!
- I haven’t found any formal data on this, but I have personally tested my temperature many times before, during, and after taking hot baths, to try to get a sense of how much you can tinker with your core body temperature. Normal body temperature, measured orally, is usually reported as 36.8±0.5°C, for a total range of 1˚C. (However, a 2002 review reported a normal range twice as large, 36.7±1°C.) After 5-10 minutes in a bath so hot it’s barely tolerable, I’ve seen my own temperature get up to 38.5. It falls back into the normal range really fast, within minutes.
- Viitasalo JT, Niemela K, Kaappola R, et al. Warm underwater water-jet massage improves recovery from intense physical exercise. Eur J Appl Physiol Occup Physiol. 1995;71(5):431–8. PubMed 8565975 ❐
- Waring RH. Report on Absorption of magnesium sulfate (Epsom salts) across the skin. Unpublished. 2006. PainSci Bibliography 56301 ❐
Magnesium and sulfates in the blood were measured and found to be higher after people had Epsom salts baths. No therapeutic effects were studied or claimed. The results seem straightforward. However, this study was never peer-reviewed and published in a scientific journal or repeated by other scientists — it has only ever been available as a PDF from the website of the Epsom Salt Council, an industry lobby group that is “Eager to let everyone know the benefits of our product … to help spread the word about the wonder that is Epsom salt. You see, we're wild about this pure, time-tested mineral compound and its dozens of uses.”
Despite the obvious potential for bias here, Waring told me in personal correspondence that her experiment was straightforward and conducted independently.
- Eisenkraft A, Krivoy A, Vidan A, et al. Phase I study of a topical skin protectant against chemical warfare agents. Mil Med. 2009 Jan;174(1):47–52. PubMed 19216298 ❐
Hat tip to reader Bryan B. who found this study and noted that it seems to “clearly demonstrate that magnesium doesn't penetrate the skin — at least that of Israeli soldiers.” Basically, it was a safety study of a lotion — with a lot of magnesium in it — that was developed “to improve protection against chemical warfare agents.” Soldiers were not poisoned by the magnesium. Indeed, it didn’t appear to cross the skin at all: “there were no significant differences in magnesium levels between the placebo and the study groups in any of the applications.” The delivery system — lotion — could be quite different than soaking in water with dissolved magnesium sulfate. But I agree it's pretty strong evidence that absorption is minimal or nil, which is certainly at odds with Waring’s result.
- The colorful history of medicine and quackery is overflowing with people who “swore by” treatments that were bizarre and perilous. Even the worst had fans. People believe what they want to believe. For more information, see Popular but Weird & Dangerous Cures: The most dangerous, strange, and yet popular snake oils and “treatments” in history (and why anecdotes and testimonials cannot be trusted).
- Here’s one good theory suggested by reader Bruce M.: “Lungs have a large surface area, and amount to a radiator that sheds a lot of body heat. So huffing is a cooling mechanism that works when sweating doesn’t, which must extend the time that one can tolerate hot-water immersion.” That makes sense, and I suspect there’s more to it besides.