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A Better Hot Bath

Tips for getting the most out of the oldest form of therapy

2,500 words, updated Aug 21st, 2014
by Paul Ingraham, Vancouver, Canadabio
I am a science writer, the Assistant Editor of ScienceBasedMedicine.org, and a former Registered Massage Therapist with a decade of experience treating tough pain cases. I’ve written hundreds of articles and several books, and I’m known for sassy, skeptical, referenced analysis and a huge bibliography. I am a runner and ultimate player, and live in beautiful downtown Vancouver, Canada. • full bioabout SaveYourself.ca

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. 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. You will probably be surprised by some of them.

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

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.

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.1

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.

An artificial fever has its uses, but it can also have some unpleasant side effects.

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, perhaps to “release” muscle knots (trigger points). 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 an amazing 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, and trap a ball between your body and the bottom or back of the tub to rub your back muscles — your buoyancy allows for excellent control over moderate pressures.

The Bath Trick

Run a hot bath, and trap a ball between your body and 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 bouyancy in the water allows finely tuned control over moderate pressure on your trigger points. Applying a little more or less pressure is as simple as rising up in the water a little, or submerging more of yourself.

Combine a hot bath with stretch

Stretching is not generally as useful as most people imagine,2 but it’s not useless either. Stretching might be effective for relieving muscular aches and pains, possibly because it helps trigger points, or maybe just because it’s like scratching an “itch.”3 But it’s not exactly guaranteed to work miracles — lots of people fail to get rid of muscle knots just by stretching.

Regardless, doing it in a hot bath probably improves the odds of success:

If you’re going to stretch, then stretch in the bath.

Or in a pool!

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).6 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 think7, and there’s actually a genuine danger in the modern craze for constantly sucking on a bottle of water: you can drink too much.8 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 certain 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 pretty obvious to all of us 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.9 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! 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.10

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.

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 pressure on the spot. 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!

ZOOM

I think that tub needs some groovy flames.

ZOOM

I think that tub needs some groovy flames.

Should you add 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 them11 — which is actually a bit biologically surprising, and had never been proven before. And, meanwhile, other evidence pretty strongly suggests just the opposite.12 (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,13 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:

Almost always use a hot bath for low back pain

A hot bath is not only a much 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 costs to fill a bath.) About 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 very rarely the case.

The great majority of low back pain is essentially muscular in nature, contrary to the popular and mistaken medical view that it’s usually caused by something “mechanical” like a intervertebral disc herniation.

Specifically, the cause of most back pain is myofascial trigger points (“knots” in your muscles), which can cause far more grief than most people realize — and yet they are relatively treatable. A little reassurance, rubbing, and a hot bath go a surprisingly long way, even with the most horrendous case of low back pain. A hot bath is amazingly good therapy for back pain, and the price sure is right.

Once again, trigger points are eased by heat, and usually 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:

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.14

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:

About Paul Ingraham

I am a science writer, former massage therapist, and assistant editor of Science-Based Medicine. I have had my share of injuries and pain challenges as a runner and ultimate player. My wife and I live in downtown Vancouver, Canada. See my full bio and qualifications, or my blog, Writerly. You might run into me on Facebook and Google, but mostly Twitter.

Notes

  1. 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. BACK TO TEXT
  2. SY Ingraham. Quite a Stretch: Stretching science shows that a stretching habit isn’t doing much of what people hope. SaveYourself.ca. 12775 words. BACK TO TEXT
  3. 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. BACK TO TEXT
  4. SY Ingraham. Thixotropy is Nifty, but It’s Not Therapy: A curious property of connective tissue is often claimed as a therapy. SaveYourself.ca. 763 words. BACK TO TEXT
  5. The cause of trigger points is only theoretical, so it’s hard to be sure. See Trigger Point Doubts. BACK TO TEXT
  6. The idea of “toxins” is usually used as a tactic to scare people into buying de-toxifying snake oil of one sort or another. Exactly what toxins and how they are eliminated is never properly explained — because the sellers do not know. The body deals with unwanted molecules in many ways: it eliminates, recycles, and traps. Some can’t be safely handled at all (metals). The only truly detoxifying treatments help the body eliminate or disarm molecules the body cannot process on its own (or not fast enough), like a stomach pump or an antivenom. Anything less is a scam. For instance, saunas do not “detoxify” as often claimed: they just mildly stimulate one normal excretion pathway. I cover the specific idea of “flushing” toxins in Should You Drink Water After Massage? (Massage is wonderful for all kinds of reasons — it doesn’t need the support of the idea that it detoxifies.) For more general consumer advocacy and education about toxins, see “Detoxification” Schemes and Scams (from QuackWatch.org). BACK TO TEXT
  7. SY Ingraham. Water Fever and the Fear of Chronic Dehydration: Do we really need eight glasses of water per day? SaveYourself.ca. 2643 words. BACK TO TEXT
  8. Almond et al. Hyponatremia among runners in the Boston Marathon. New England Journal of Medicine. 2005. PubMed #15829535.

    According to this report, over-hydrating (hyponatreamia) “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.”

    BACK TO TEXT
  9. It has been shown that local heating never “penetrates” much deeper into the tissue than a centimeter, 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! BACK TO TEXT
  10. Viitasalo et al. Warm underwater water-jet massage improves recovery from intense physical exercise. Eur J Appl Physiol Occup Physiol. 1995. PubMed #8565975. BACK TO TEXT
  11. Waring. Report on Absorption of magnesium sulfate (Epsom salts) across the skin. Unpublished. 2006.

    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, as of early 2013, this study has still not yet been peer-reviewed, published in a scientific journal or repeated by other scientists. Also note that one of the only other magnesium absorption studies I know of (Eisenkraft et al) came to the opposite conclusion — no absorption — and is quite persuasive.

    BACK TO TEXT
  12. Eisenkraft et al. Phase I study of a topical skin protectant against chemical warfare agents. Mil Med. 2009. 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.

    BACK TO TEXT
  13. 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 and Dangerous Cures: The most dangerous, strange, and yet popular snake oils and “treatments” in history (and why anecdotes and testimonials cannot be trusted). BACK TO TEXT
  14. Here’s one good theory suggested by reader Bruce M.: “Lungs have 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 complete sense. And I suspect there’s more to it besides. BACK TO TEXT