Most of what people believe about baths is folklore. Daniel got hit with two of those, and it cost him years of baths.
And here's what's funny. The actual research on immersion bathing is better than the folklore ever was. He was robbed.
So Daniel wrote in. And I want to set this up properly, because it's a personal one. He used to love baths. Then a friend told him that sitting in a tub is essentially stewing in your own dirt. Then a hotel placard informed him how much more water a bath uses than a shower. And that combination, the disgust plus the guilt, ruined baths for him. He's been a shower person ever since.
Two sentences did all that damage.
Two sentences. So today he got back in. He climbed in with little Ezra first, and then Ezra was removed, because Hannah's position was that it's bad enough having Daniel smell like a Franciscan friar, let alone the baby. Then he dropped in the Zum frankincense and myrrh salts he'd been saving for exactly this.
And he's writing to us from the tub.
He is writing to us from the tub, sick, achy, and he wants to know several things. What are the real benefits of a bath beyond hygiene? Is a bath therapeutic in a way a shower cannot match, particularly on a day like this one? What does the research say about the heating properties? Are frankincense and myrrh bath salts actually doing anything? And can you use those salts with a baby, or only if they're specifically labeled baby-safe? He presumes the answer is no, but he thought he'd ask.
His presumption is correct, and we'll get there.
So let's find out whether Daniel was robbed of baths for no reason.
He was.
Start with the framing, then. Because his intuition is that a bath does something a shower can't, and I think most people would guess that's just the smell and the lying down.
The intuition is right and the reason is wrong. It isn't the smell. It's that immersion is a fundamentally different physical event from standing under a spray. A shower applies heat to your surface. A bath applies heat to your whole body while removing the gravitational load. Those are not the same intervention, and the body responds differently.
And there's a head-to-head study.
There's a head-to-head study. That's the thing that surprised me when I went looking. Most of this literature is balneotherapy, spa towns, mineral water, that whole European tradition, which makes it hard to separate the water from the vacation. But there's one trial that just put bathing against showering directly.
Give me the shape of it.
Two thousand eighteen, Goto and colleagues, randomized crossover. Thirty-eight people enrolled, thirty-three made it through the analysis. Two weeks of immersion bathing, forty degrees Celsius, ten minutes, versus two weeks of showering. Same people, both arms, crossover design.
Which controls for the person, at least.
Which controls for the person. And immersion bathing won on fatigue, on stress, on pain, and on a self-reported "smile" measure. All of those at p less than zero point zero five. It also beat showering on the general health and mental health subscales of the SF-8, and on social functioning, and on the mental component summary.
Smile is a strange outcome measure.
It's a Japanese wellbeing instrument. But the mood data is the part I'd point at. The POMS scores were significantly better during bathing for tension-anxiety, depression-dejection, and anger-hostility. That's three separate mood dimensions moving in the right direction.
So it isn't just "I enjoyed my bath." It's measurable on standardized instruments.
On standardized instruments, in a crossover design, with the same subjects doing both conditions. It's a small trial. Thirty-three people analyzed is not a lot, and the authors say so themselves. But the direction is consistent and the mechanism they propose is real.
Which is?
Immersion exerts a hyperthermic action. Core temperature climbs, blood flow increases, and the paper's language is that this induces increased blood flow and metabolic waste elimination. Heart rate goes up forty to fifty percent during immersion. And then buoyancy, which is the part people forget, reduces gravitational load on the body.
Forty to fifty percent on heart rate. That's not trivial.
It's a real cardiovascular event. Which is also why the same paper carries a caution we should come back to, because it cuts the other way for some people.
Hold that. Because the strongest finding in this whole literature isn't the mood data. It's sleep.
It's sleep, and it's not close. Two thousand nineteen, Haghayegh and colleagues, systematic review and meta-analysis in Sleep Medicine Reviews. Seventeen studies pooled, thirteen of them -analyzed. Water-based passive body heating at forty to forty-two and a half degrees Celsius, scheduled one to two hours before bedtime, for as little as ten minutes.
Ten minutes.
Ten minutes. And it significantly shortened sleep onset latency, and improved self-rated sleep quality and sleep efficiency. That's the most actionable finding in the entire episode, and it's the one nobody acts on.
Here's the part I want you to explain, because it's backwards from what I'd expect. A hot bath makes you warm. Sleep is associated with cooling. How does warming yourself up make you sleep?
Because the bath doesn't make you sleepy by making you warm. It makes you sleepy by making you cool down afterward.
Say that again.
The mechanism is the distal-to-proximal skin temperature gradient. When you're in warm water, blood perfusion increases to your palms and your soles. Those are your radiator surfaces. More blood flow out there means more heat dumped from your core to the environment. So you get out, and your core temperature drops faster than it otherwise would. And that core temperature drop is one of the triggers for sleep onset.
So the bath is a cooling intervention with a warming preamble.
That's exactly what it is. And it explains the timing window. One to two hours before bed is when the core temperature drop is happening. Take the bath right before you get in bed and you've missed the window.
That's a useful thing to know and I had it backwards.
Most people do. The folk version is "a hot bath relaxes you." The real version is "a hot bath accelerates a cooling cascade that your sleep system reads as a signal."
Now the aches. Because that's the actual reason Daniel got in the tub today.
The balneotherapy literature is where the ache evidence lives, and the biggest single dataset I found is a cohort from Southern Ethiopia, two thousand twenty-one, Gebretsadik and colleagues. Twelve hundred and seventy-nine people at hot springs. Eighty-three point two percent reported complete relief of their presenting complaints after bathing.
Complete relief. That's a big number.
It's a big number and it's a single-arm cohort, so there's no control, and people who travel to a hot spring and pay for it are not a neutral sample. But look at why they came. Eighty-eight point nine percent came for joint pain. Fifty-two point two percent for muscle pain. And people who bathed for three days or more showed significant therapeutic effects on musculoskeletal disorders.
So the population is aches and the outcome is relief.
That's the population and that's the outcome. Now here's where it gets interesting, because there's a trial that tried to separate the water from the heat.
The mineral question.
Two thousand twenty, Rapolienė and colleagues, randomized controlled trial, one hundred and forty-five people, five groups. Mineral water baths produced small effects on pain and medium effects on sleep quality, with reduced CRP and ESR. Real inflammatory markers moving.
And the control?
Plain tap water was effective in sixty percent of cases.
Sixty percent.
Sixty percent. So the mineral content is doing something at the margins, mostly in the highest-mineral group, and the effects lasted up to two months there. But the bulk of the benefit is the heat. Warm water, applied to a body, for a duration.
Which is a problem for the premium salt industry.
It's a problem for the premium salt marketing. It's not a problem for the experience, and we'll separate those two things properly in a minute.
What about the mechanism for the ache relief specifically? Because "warm water feels good on a sore back" is not an explanation.
There's a review from last year, Fedorchenko and colleagues, on sauna therapy in rheumatic disease, and it lays out the inflammatory picture. Heat exposure reduces pro-inflammatory agents. TNF-alpha, CRP, PGE2, LTB4. And it promotes IL-10, which is anti-inflammatory.
So there's a plausible pathway from heat to reduced inflammation.
There's a plausible pathway. I'd flag that the review is about sauna, not baths, and the two aren't identical. But the heat exposure is the shared variable, and the direction of the effect is consistent with what the balneotherapy trials show.
Now the cold. Because that's what Daniel actually has.
I went looking for direct evidence that a hot bath treats cold symptoms. I could not find it.
Nothing?
Nothing. Searches for hot bath and common cold symptom relief return no clinical trials. I want to be honest about that, because it would be easy to wave at the vasodilation and the relaxation and imply there's evidence behind it. There isn't direct evidence.
So what's the honest version?
The honest version is that the relief Daniel is describing is real and the mechanism is probably indirect. Heat causes vasodilation and muscle relaxation, which addresses the achy part. And the sleep improvement is well established, and sleep matters when you're sick. But "a bath treats a cold" is not a claim the literature supports.
It treats the misery of the cold.
That's a fair way to put it.
So that's the mechanism. Now let's talk about what's actually in the tub.
The frankincense and myrrh.
Which Daniel has been saving for an occasion, and which occasion turned out to be a head cold.
First, what they are. Frankincense is an oleo-gum-resin from Boswellia trees. The essential oil is rich in alpha-pinene, limonene, p-cymene, and a range of other terpenes. Myrrh is a Commiphora resin. These are the two substances that show up in the nativity story, and they've been traded for three thousand years, which is a longer track record than most things in a bathroom.
And the evidence?
The evidence is thinner than the marketing. There's a two thousand twenty-four study, Wu and colleagues, testing a compound essential oil that included Boswellia carterii and Commiphora myrrha on neck and shoulder pain. It found significantly stronger anti-inflammatory and analgesic effects than the single oils alone.
In what?
In mice.
Of course.
In mice. And I want to be clear about that, because "Boswellia and Commiphora reduce neck pain" sounds like a human finding and it isn't. Then there's a two thousand twenty-two randomized double-blind placebo-controlled trial, Hawkins and colleagues, on an inhaled blend that included frankincense. It boosted energy and reduced fatigue in post-COVID women.
Inhaled.
Inhaled. A proprietary blend, breathed, not dissolved in a tub. So the oils have some evidence behind them, in topical and inhaled formats, mostly in animal models or specific clinical populations.
And the bath-salt format specifically?
No study tests frankincense and myrrh bath salts in water. I looked. The evidence is for the oils, not for the diluted soak.
So the honest answer to Daniel's question is that the salts are doing less chemistry than the label implies.
The heat is doing the work. Remember the sixty percent figure from the Rapolienė trial. Plain tap water was effective in sixty percent of pain cases. If that's the baseline, the incremental contribution of the frankincense is small.
And I want to be careful here, because that sounds like I'm calling it a waste of money.
It isn't a waste of money. The smell is part of the intervention. The ritual is part of the intervention. Daniel has been saving these salts for an occasion, and the act of deciding today is the occasion is itself doing something. I'd just separate the ritual value from the pharmacological claim.
The ritual is real and the chemistry is unproven.
That's the honest split.
What's actually in the packet?
Sea salt, magnesium sulfate, which is Epsom salt, sodium chloride as a dendritic salt, fragrance with essential oils, meadowfoam seed oil, shea butter extract, rosemary leaf extract. No detergents, no parabens, no phthalates.
And the magnesium. Because that's the claim everyone makes about Epsom salts.
The claim is that magnesium absorbs through the skin. I found no PubMed results supporting transdermal magnesium absorption from Epsom salt baths. It's a contested claim and the literature I could find doesn't back it.
So the Epsom salt is in there for the feel of the water.
For the feel of the water, and for the tradition. It's been sold as a bath additive since the seventeenth century. That doesn't make it pharmacology.
Now the baby question, because Daniel asked directly and his presumption was no.
His presumption is correct. Essential oils should not be used on babies under three months at all. That's the American Association of Naturopathic Physicians position. Some guidance extends it to six months.
And the product itself?
The Zum product is labeled, on the retail listing, as formulated for adults and designed for adult use. That's the manufacturer's own positioning. It is not a baby product.
Is there any legitimate use of essential oils in infant bathing?
There's a two thousand twenty-five review in the CURARE Journal of Nursing on aromatherapy in neonatal care. It notes that a small amount of essential oil is sometimes added to neonatal bath water for relaxation, but it has to be done cautiously because of physiological sensitivity, and oral administration is not recommended at all.
And the dilution?
For infants over three months, the maximum dilution is zero point two five to zero point five percent in a carrier oil. That's a fraction of a percent. The Zum packet is not formulated to that standard and isn't labeled for it.
So Daniel's instinct was right and Hannah's instinct was also right, for a different reason.
Hannah's instinct was aesthetic and Daniel's was safety, and they arrived at the same place. Ezra got a plain bath.
Good. Now I want to go back and dismantle the two things that ruined baths for him, because that's the actual arc of this episode.
Start with the dirt.
"You're stewing in your own dirt." I went looking for a study that compares bath water to shower cleanliness, and there isn't one.
There isn't one. Searches for bathing versus showering and skin microbiome and soap comparisons return nothing relevant. This is folk wisdom that has never been tested.
Which is remarkable, given how many people believe it.
It's remarkable, and it's the kind of claim that survives because it sounds like it must be true. You're sitting in water. Water gets dirty. Therefore you're dirty. But the inference doesn't hold, because soap and rinse-off matter more than the delivery method.
And the practical version, which is what you actually do?
You rinse off after. Which is what people have always done. The bath is for soaking, the rinse is for cleaning, and that division of labor solves the problem the claim is worried about.
So the dirt claim is unsubstantiated and the fix is a thirty-second shower afterward.
That's the whole thing.
Now the water guilt, which is where this gets interesting, because the numbers flip depending on which numbers you use.
The EPA WaterSense figure is the one on the hotel placard. A shower uses ten to twenty-five gallons. A bath takes up to seventy gallons.
Worst case against worst case.
But the Water Research Foundation did a national study in two thousand sixteen, and the averages are seventeen gallons for a shower and thirty gallons for a bath.
So the typical bath is roughly two typical showers.
Roughly. And a long shower exceeds a bath. A twenty-minute shower at two and a half gallons a minute is fifty gallons. That's more than the average bath.
And there's an even starker comparison from the Department of Energy figures.
Consumer Reports noted in two thousand eight that the DOE figures were twelve gallons of hot water for a shower versus nine gallons for a bath. The bath uses less hot water, because you fill it once and you're done, and the shower runs the whole time.
So the guilt was based on a comparison that only holds if you take short showers and deep baths.
And one more number that reframes the whole thing. The EPA benchmarks put baths at one point nine percent of indoor water use. Showers are eighteen point eight percent.
Ten times.
Ten times. If you're optimizing household water, the shower is the thing to look at, not the tub. Skipping one long shower saves more than skipping a bath.
Daniel was guilt-tripped by a placard that picked the least favorable comparison available.
He was guilt-tripped by a hotel that wanted to save money on hot water and dressed it up as environmentalism.
Which is a different episode. Now the safety tension, because you flagged it earlier and it's real.
The Goto paper itself carries the caution. For the aged generation, especially patients with cardiovascular disease, full-body immersion would be unbeneficial, because hydrostatic pressure causes venous return load.
Explain that.
When you're submerged to the chest, the water pressure pushes on the veins in your legs and abdomen. That pushes blood back toward the heart. For a healthy person that's fine, it's part of what makes immersion feel good. For someone with a compromised heart, that's extra volume the heart has to move, and it can be a problem.
So the same property that makes it therapeutic makes it risky for some people.
The same property. Hydrostatic pressure is not a side effect. It's the mechanism. And there's a documented phenomenon in Japan of elderly people dying during winter bathing, which Tochihara and colleagues wrote about this year. Hot water, cold room, cardiovascular load, and a population that's already vulnerable.
So the caution is take a warm bath, not a scalding one, and if you have cardiac issues, talk to someone before you make it a habit.
That's the caution. It's not a reason to avoid baths. It's a reason to know what you're doing.
One more question Daniel didn't ask but I want answered. Is there a dose? Is there a minimum effective bath?
Ten minutes is the floor in the sleep literature. Forty degrees is the temperature. And the timing is one to two hours before bed. Those are the three parameters, and they're consistent across the studies.
Ten minutes, forty degrees, ninety minutes before bed.
That's the protocol with the best evidence behind it.
Hilbert.
Hilbert: Did anyone ever figure out why the six fifteen man needed it every morning.
What?
Hilbert: I worked a bathhouse. Historic hotel, clawfoot tubs, brass taps, the whole thing. I drew baths for guests. Part of the job was getting the temperature right by hand, because the gauges were decorative. You learned what a hundred and four degrees felt like on the inside of your wrist.
How long did you do that?
Hilbert: Two winters. There was a regular, came in every morning at six fifteen exactly, and he said the bath was the only thing that kept his back from seizing up. Never told me what he did. Tipped like a surgeon.
Every morning.
Hilbert: Every morning. I had the tub filled before he got there. He was in and out in twenty minutes. And I'll tell you the thing your research misses. The dirt doesn't stay in the water. It rinses off. What stays in the water is the soap and the oils, which is why you rinse after. Your friend had it backwards.
So the salts go in before, not after.
Hilbert: Before. If you put them in after you're sitting in grit. And the hotel took the tubs out eventually. Water saving. The regulars were furious. I was there for that meeting.
I bet you were.
Hilbert: I have to go. Somebody's waiting to be let in and I'm the only one with the key.
The six fifteen man. We never found out what he did.
A surgeon who tips like a surgeon is not a satisfying answer.
It's the only one we have.
Here's what I keep coming back to. The frankincense and myrrh bath-salt format has never been tested. Somebody should run that study. And the cold-symptom relief is plausible but unproven, which is its own interesting gap.
The sleep finding is the one to take seriously. Ten minutes, forty degrees, ninety minutes before bed. That's the protocol with real evidence behind it, and the heat is doing most of the work, not the minerals.
Thanks to Hilbert Flumingtop, our producer, who apparently has keys to things.
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