Bath Salts: From Roman Thermae to Your Bathroom Apothecary

In 1618, somewhere on Epsom Common in Surrey, a farmer named Henry Wicker noticed something odd. His cattle refused to drink from a small spring trickling through the ground. The water, when he tasted it himself, was intensely bitter. He had stumbled onto one of the richest natural sources of magnesium sulfate in England, and within a generation, his muddy little spring would transform a quiet village into one of Britain’s first spa towns.

The cows, it turns out, knew something. Bitter water meant minerals. And minerals, dissolved in warm water and applied to the human body, have been the subject of medical attention for at least 2,500 years.

The Oldest Medicine

The formal name is balneotherapy: the practice of bathing in mineral-rich waters for healing. It sounds clinical now, but for most of recorded history, it was simply what you did when you were sick.

Hippocrates, writing in the fifth century BCE, classified waters by their mineral content in On Airs, Waters, and Places. He noted that waters from soil producing thermal springs, those containing iron, copper, sulphur, alum, or bitumen, had distinct effects on the body. They were “hard and of a heating nature,” he wrote, difficult to digest and slow to pass. The best waters came from elevated ground: sweet, clear, capable of bearing a little wine. This was not mysticism. This was early empirical observation about what different dissolved minerals do to a human system.

The Greeks built their Asclepieia, the great healing temples of Asclepius, near mineral springs with good reason. At Epidaurus, the most famous of them all, a hydraulic system of channels and settling basins (parts still visible today) brought mineral water from the springs of Mount Kynortion to two distribution points: the Doric Spring and the Sacred Spring. Archaeological excavations beginning in 1881 uncovered inscribed stone stelae dating to around 350 BCE, recording approximately seventy healing narratives. Water was central to the cure.

The Romans, characteristically, industrialized the idea. At Aquae Sulis (modern Bath, England), three hot springs pump over a million liters of geothermal mineral water per day at temperatures reaching 46°C. The temple complex was built around 60-70 AD and expanded over the next three centuries, eventually enclosing a full bathing circuit: the caldarium (hot bath), tepidarium (warm bath), and frigidarium (cold plunge). The Gesta Stephani (written c. 1148) recorded that sick people still came from across England to wash away their infirmities in those same waters, seven centuries after the Romans had left.

Then there is the Dead Sea, a body of water unlike any other on earth. Its salt composition is inverted compared to ocean water: while ocean salt is roughly 85% sodium chloride, Dead Sea salt is only 30.4% sodium chloride. The dominant mineral is magnesium chloride at 50.8%, with calcium chloride at 14.4% and potassium chloride at 4.4%. This unusual chemistry has made it a destination for skin treatment since antiquity, though some of the marketing claims around it deserve scrutiny. The popular story that Cleopatra bathed in Dead Sea salts and maintained exclusive rights to its mineral deposits is almost certainly invented. The ancient source most often cited, Josephus’s Antiquities of the Jews (XV.96), records that Antony gave Cleopatra the balsam-producing revenues near Jericho, which Herod then leased back from her. There is no mention of bathing. The Dead Sea cosmetics legend appears nowhere in ancient texts.

In Japan, the toji tradition (hot spring cure) predates written records. The Kojiki (712 AD) records Prince Karu’s exile to Iyo Province (home of Dōgo Onsen), and the Nihon Shoki (720 AD) records Emperor Jōmei staying at Arima Onsen for roughly three months in 631 AD. The practice of extended therapeutic residence at hot springs, weeks or months rather than a quick visit, spread among common people during the Edo period (1603-1868) and continues today.

European spa culture followed a parallel path. At Baden-Baden, Roman soldiers bathed in thermal springs from the second century AD, their bath infrastructure still excavated beneath the modern Friedrichsbad. The town’s waters, the hottest in Baden-Württemberg, were prescribed for war injuries. At Karlovy Vary in Bohemia, Emperor Charles IV granted the hot springs town status in 1370, according to legend after his hunting dog was burned by a spring that turned out to reach 73.4°C. By the sixteenth century, Paracelsus was prescribing patients at Baden-Baden to bathe for up to twelve hours a day. In 1562, Dr. William Turner published The Book of the Natures and Properties of the Baths of England, listing over sixty disorders that could benefit from bathing. The medical profession had officially adopted the waters.

The Bitter Water of Epsom

Back to that reluctant cattle. Tradition holds that Henry Wicker discovered the Epsom spring in 1618, though the earliest written accounts date from the 1640s. Dudley North, the third Lord North, claimed in his Forest of Varieties (1645) that he was the one who first brought the Epsom waters to public attention. An Abram Booth journal from 1629 provides one of the earliest descriptions of actually visiting the wells.

What is not disputed is the water’s effect. It was a powerful purgative, and word spread. By 1621, a wall had been built around the spring and a shed erected for invalids. After the Restoration of Charles II in 1660, Epsom transformed rapidly. The king himself became a regular visitor (it was at Epsom that he met the actress Nell Gwyn). Samuel Pepys recorded visiting the wells in 1663 and again in 1667, arriving by eight in the morning to find much company already gathered and drinking the water. By the 1690s, the Lord of the Manor, John Parkhurst, had built a brick wellhouse, a coffee house, gaming rooms, bowling greens, and shops. Epsom was a proper resort.

The science followed the spectacle. In 1695, Dr. Nehemiah Grew, a physician, botanist, and Fellow of both the Royal College of Physicians and the Royal Society, published the first chemical analysis of the Epsom waters. His work, Tractatus de salis cathartici amari in aquis Ebeshamensibus (published in English in 1697 as A Treatise of the Nature and Use of the Bitter Purging Salt Contain’d in Epsom and Such Other Waters), identified magnesium sulfate as the active compound. In 1698, Grew received a Royal patent for manufacturing the salt cheaply in quantity. This promptly led to a commercial dispute with two apothecaries, the Moult brothers, who published an unauthorized translation and undercut his prices. The mineral was formally named epsomite in 1806 by the French mineralogist Jean-Claude de La Métherie.

What Grew had done was remarkable: he had isolated the first mineral compound from a natural spring and connected its chemistry to its medical effects. Epsom salt, magnesium sulfate heptahydrate (MgSO₄·7H₂O), was technically not a salt at all but a mineral compound. And it could now be manufactured, bottled, and sold without anyone needing to visit Surrey.

By the 1720s, Epsom’s popularity as a spa had declined, overtaken by Bath and Tunbridge Wells. But the compound it gave its name to had become a pharmacy staple across Europe, prescribed for everything from constipation to muscle pain. It still is.

What the Science Says (And What It Doesn’t)

This is where honest writing about bath salts gets uncomfortable, because the science is neither as strong as the wellness industry claims nor as empty as skeptics suggest.

The magnesium absorption question. The most-cited study on transdermal magnesium absorption from Epsom salt baths was conducted by Dr. Rosemary Waring at the University of Birmingham around 2006. It tested 19 subjects (staff recruited from her own department), all healthy, bathing at 50-55°C for 12 minutes. Sixteen of nineteen showed a rise in plasma magnesium levels. The study was never published in a peer-reviewed journal. It appeared as a report on the website of the Epsom Salt Council, an industry body. There was no control group. The bath temperature was significantly hotter than what most people actually use (37-40°C is standard). This is, essentially, the entire evidence base for the specific claim that Epsom salt baths deliver magnesium through the skin. One small, uncontrolled, industry-funded, non-peer-reviewed study. That does not mean the claim is false. It means it is unproven.

What IS well-established. Warm water immersion itself, independent of any minerals dissolved in it, produces measurable physiological effects. A 2019 integrative review published in International Journal of Environmental Research and Public Health found that immersion in thermoneutral water (around 34.5°C) decreases plasma norepinephrine, epinephrine, beta-endorphin, and cortisol. The review concluded that such immersion “can be viewed as stress reducing.” Separate studies have shown cortisol reduction from warm foot baths (40-43°C for 15 minutes over 14 days) and from extended heat exposure. The warm water itself is doing something. The question of whether dissolved minerals add to that effect beyond the baseline is, scientifically, still open.

Dead Sea balneotherapy is a different story. Here, the clinical evidence is genuinely strong. A 2012 systematic review by Katz et al. in Seminars in Arthritis and Rheumatism analyzed 31 studies on rheumatologic diseases and 50 on psoriasis, concluding that Dead Sea treatments are beneficial with a good safety profile. Published trials show PASI (Psoriasis Area and Severity Index) scores decreasing by over 80% after four weeks of treatment, with nearly half of patients achieving complete clearance. A 2001 study in Clinical Rheumatology demonstrated significant reduction in active joints for psoriatic arthritis patients. But there is a complication: the Dead Sea sits at over 430 meters below sea level, creating a unique atmospheric UV filtering environment. Researchers believe the therapeutic effect comes from the combination of minerals and this unusual UV exposure, not minerals alone. The Dead Sea is not just special salt. It is a specific place.

The “84 minerals” in Himalayan pink salt. This claim traces to a 2003 book, Water & Salt: The Essence of Life by Barbara Hendel and Peter Ferreira. Spectral analysis can indeed detect approximately 84 elements in Himalayan pink salt from the Khewra mine in Pakistan. The salt is also 96-99% sodium chloride. A peer-reviewed analysis (Fayet-Moore et al., Foods, 2020) confirmed that while trace minerals are present at higher levels than in table salt, the amounts are “too low for nutritional significance without exceedingly high intake” that would far exceed safe sodium guidelines. Eighty-four is a real number. Its practical meaning is close to zero.

The Salts

A quick chemical guide to what you are actually putting in the water.

Epsom salt (magnesium sulfate heptahydrate, MgSO₄·7H₂O). Not technically a salt. Fine crystals that dissolve quickly in warm water. The workhorse of bath salts, inexpensive and widely available. Whatever the transdermal magnesium evidence says or doesn’t say, it has been used in baths for four centuries and remains the most common therapeutic bathing mineral.

Sea salt. Primarily sodium chloride with trace minerals (zinc, potassium, iron) retained from evaporated seawater. Varies by source: Celtic grey salt, Mediterranean, Pacific. Each has a slightly different trace mineral profile, though the differences are subtle.

Dead Sea salt. Chemically distinct from all other salts. Only 30.4% sodium chloride versus the ocean’s 85%. Dominated by magnesium chloride (50.8%), with significant calcium and potassium chloride. More expensive, but genuinely different in composition. If you want to recreate anything resembling a Dead Sea mineral bath at home, this is the only salt that gets close.

Himalayan pink salt. Rock salt mined from ancient seabeds in Pakistan (primarily the Khewra mine). The pink color comes from iron oxide. It is 96-99% sodium chloride. Use it for its aesthetic appeal and as part of a blended mix, but know what it is and what it is not.

Baking soda (sodium bicarbonate). Not a salt in the bath-salt sense, but a useful addition. It softens hard water, neutralizes skin pH, and creates a silkier feel. Use 2-4 tablespoons per bath.

The Apothecary

Here is a consolidated recipe and four targeted blends. The original DIY approach, with its seven blends and three pages of instructions, was overkill. You need one master formula and a few variations.

Sleep blend: 12 drops lavender (Lavandula angustifolia), 8 drops Roman chamomile, 5 drops cedarwood atlas, 3 drops vetiver. Use 1-2 hours before bed. The warm bath raises core body temperature; the subsequent cooling triggers sleep signals.

Muscle recovery blend: 10 drops eucalyptus radiata, 8 drops peppermint, 6 drops rosemary (ct. cineole), 4 drops black pepper. Use within a few hours of exercise. Consider extra Epsom salt (up to 3 cups total). Avoid rosemary during pregnancy.

Stress relief blend: 10 drops bergamot (FCF preferred), 8 drops clary sage, 6 drops frankincense, 4 drops ylang ylang. Practice slow breathing while soaking: inhale for four counts, hold for four, exhale for eight.

Respiratory blend: 12 drops eucalyptus radiata, 8 drops tea tree, 5 drops peppermint, 3 drops ravensara. For congestion and colds. Lean over the tub before getting in to inhale the steam directly.

Essential oil safety: Never add essential oils directly to bath water. They do not disperse and can cause skin irritation or burns. Always pre-dilute in carrier oil or mix into your salt blend first. Patch test new blends on the inner arm 24 hours before a full bath. For more on working with essential oils and their history, see our articles on quintessence and the spagyric tradition and the art of perfumery.

The Ritual and the Evidence

Here is what we actually know, stripped of marketing and stripped of dismissal.

Warm water immersion reduces cortisol. It activates the parasympathetic nervous system. It measurably changes heart rate, blood pressure, and hormone levels. These effects are documented in peer-reviewed research and they do not require any minerals at all. Plain warm water does this.

Dead Sea mineral baths, in the specific environmental conditions of the Dead Sea, produce clinically significant improvements in psoriasis and certain arthritic conditions. This is also documented.

Whether Epsom salt baths deliver meaningful magnesium through the skin remains scientifically unproven, based on one weak study with significant methodological problems. Millions of people report feeling better after Epsom salt baths. Whether that is magnesium, warmth, ritual, placebo, or some combination, nobody has rigorously tested.

The ancient practitioners did not have the chemistry. They had something else: thousands of years of accumulated observation. Hippocrates catalogued the effects of different mineral waters without knowing what magnesium sulfate was. The priests at Epidaurus built their healing temples next to specific springs and recorded their patients’ outcomes on stone. The Japanese onsen tradition survived because people kept getting better. Nehemiah Grew, in 1695, finally connected the observation to the molecule, but the observation came first, by a very long time.

What bath salts offer, at minimum, is this: a reason to stop. Twenty minutes of warm water, a closed door, no screen, a scent you chose deliberately. The ritual of preparation, the intention behind the blend, the act of stepping into something you made for yourself. The ancient world wrapped its medicine in ceremony because ceremony itself was part of the treatment. The warm water was never the whole story.

We have the chemistry now. We also have the cortisol data and the systematic reviews and the spectral analyses. We know more than Hippocrates did about what dissolved minerals do in water. We still do not fully understand why sitting in warm mineral water makes people feel better than sitting in warm plain water, or whether it does at all, or whether the answer matters as much as the fact that people have been doing it for 2,500 years and show no signs of stopping.

Make a batch. Use it. Pay attention to what you notice.

The water is waiting.