Mixing Epsom salt with baking soda is safe and extremely common. The two ingredients are the backbone of most homemade bath soaks, foot soaks, and bath bombs. Epsom salt is magnesium sulfate; baking soda is sodium bicarbonate. In the dry state they sit together without reacting, and in the warm water of a typical bath the interaction between them is minimal at the concentrations people actually use. Where things get more interesting is in what each ingredient does on its own once dissolved, and whether combining them changes anything meaningful for your skin, your pain, or your garden.
What Happens When the Two Hit Water
In a chemistry lab, magnesium sulfate and sodium bicarbonate can react to produce magnesium carbonate, a white precipite that’s nearly insoluble in water. But that reaction favors high concentrations, high temperatures, and vigorous stirring. Research on producing lightweight magnesium carbonate industrially found that the reaction required temperatures between 70 and 80 degrees Celsius, a stirring speed of 900 rpm, and specific concentration ratios of the reactants to proceed efficiently.1Pakistan Journal of Scientific and Industrial Research. STUDIES OF REACTION MECHANISM AND PHYSICAL NATURE OF LIGHT-WEIGHT BASIC MAGNESIUM CARBONATE A bathtub is not a chemical reactor. You’re tossing a cup or two of each salt into a large volume of lukewarm water and letting them dissolve gently. Under those conditions, both compounds largely stay in their dissolved ionic forms, and you won’t see any significant precipitate forming.
The practical upshot is that mixing the two doesn’t cancel either one out. The magnesium and sulfate ions from the Epsom salt stay in the water, and the sodium and bicarbonate ions from the baking soda stay in the water. You get a bath that contains both, not a bath where one has neutralized the other.
How They Affect Bath Water Differently
Each ingredient shifts bath water in its own direction, and understanding that helps you decide how much of each to use. Epsom salt dissolved in water is roughly neutral, with a pH close to 7. It doesn’t meaningfully change the acidity or alkalinity of your bath. Baking soda, on the other hand, is mildly alkaline. Dissolving it raises the pH of bath water, typically into the 8 to 8.5 range at the amounts most people use. That’s about the same as seawater, so it’s not harsh, but it’s worth knowing if you’re thinking about skin health.
Research into bath salt formulations that combine Epsom salt and sodium bicarbonate alongside citric acid found that changing the ratio of these ingredients significantly affected both moisture content and pH of the resulting product.2IOP Science. Characterizing the quality of bath salt enriched with lemongrass essential oils as fragrant agent In that formulation, citric acid was included specifically to pull the pH downward, and the final product was quite acidic (pH 3 to 4). Without citric acid, your homemade Epsom-and-baking-soda bath will land on the alkaline side. If you want to bring the pH closer to neutral or slightly acidic, adding a splash of citric acid or apple cider vinegar is the standard approach in DIY bath recipes.
Why pH Matters for Skin
Your skin’s outer layer maintains a slightly acidic environment, generally around pH 4.5 to 5.5. This so-called acid mantle helps keep moisture in and harmful microbes out. Raising that pH, which alkaline soaks do, temporarily disrupts this barrier. For most people soaking once in a while, the disruption is trivial and skin recovers within hours. But for people with eczema or other barrier-compromised skin conditions, pH matters more. Research on restoring the skin barrier in eczema has found that mildly acidic bathing can be both safe and helpful for atopic dermatitis.3PubMed Central. Importance of Stratum Corneum Acidification to Restore Skin Barrier Function in Eczematous Diseases
This doesn’t mean baking soda baths are bad for your skin. In fact, small observational reports have documented symptom relief when baking soda is added to bathwater for aquagenic pruritus, a condition where contact with water causes severe itching. Patients found relief at concentrations ranging from 25 grams to 200 grams of baking soda added to a bath, with no adverse events reported at either level.4Journal of Integrative Dermatology. Baking Soda and the Skin: A Review of Baking Soda in Dermatology The evidence base is thin, though. These were observational reports on just two patients, not controlled trials. For the average person, a baking soda and Epsom salt bath is a mild, generally well-tolerated soak. If you have sensitive or eczema-prone skin, you might lean heavier on the Epsom salt side of the ratio and lighter on the baking soda, or add a small amount of citric acid to bring the pH down.
Epsom Salt Baths and Pain Relief
The most common reason people reach for Epsom salt is sore muscles or achy joints. There’s a persistent belief that magnesium absorbs through the skin during an Epsom salt bath and that this is responsible for the relief people feel. The evidence on this is more complicated than the marketing suggests. A review of the available literature on transdermal magnesium concluded that the idea of meaningful magnesium absorption through the skin is scientifically unsupported.5PubMed Central. Myth or Reality-Transdermal Magnesium? Your skin is a good barrier, and dissolved magnesium sulfate does not cross it efficiently enough to raise blood magnesium levels in any clinically relevant way.
That said, the subjective experience of relief is real and doesn’t require transdermal absorption to explain it. Warm water on its own relaxes muscles, improves blood flow, and reduces joint stiffness. The buoyancy of a bath takes load off joints. And a randomized controlled trial on Epsom salt baths for knee osteoarthritis found significant reductions in pain scores and improvements in daily living activities compared to a control group.6PubMed Central. Exploring the therapeutic potential of epsom salt bath on pain and intensity of knee osteoarthritis: Randomized controlled trial Whether that benefit comes from the magnesium sulfate itself, the warmth and ritual of soaking, the osmotic effect of a high-salt bath drawing fluid from swollen tissues, or some combination is hard to disentangle. But people who soak in Epsom salt baths and feel better aren’t imagining things. They may just be attributing the effect to the wrong mechanism.
Adding baking soda to an Epsom salt soak doesn’t interfere with whatever benefit the bath provides. It makes the water feel softer and silkier, which is partly a real effect (the alkalinity changes how water interacts with skin oils) and partly perception. Some people find that the combination is more pleasant than either ingredient alone, which is probably why the pairing has persisted in folk remedy traditions for generations.
Ratios and Practical Tips
There’s no single “right” ratio, because the optimal mix depends on what you’re after. For a general-purpose relaxing bath, a common starting point is roughly two cups of Epsom salt to half a cup of baking soda in a standard bathtub. This gives you a strong enough magnesium sulfate concentration to feel the characteristic smoothness of an Epsom salt bath while the baking soda softens the water without pushing the pH too high.
For a foot soak, scale down proportionally. A basin might take a third of a cup of Epsom salt and a tablespoon or two of baking soda. The water volume is much smaller, so you don’t need anywhere near as much. For muscle soreness after heavy exercise, some people go heavier on the Epsom salt, up to three or four cups per bath, and keep the baking soda the same. For a soak focused on skin softening or odor, you might increase the baking soda to a full cup.
A few things worth knowing:
- Water temperature: Warm, not hot. Very hot water can dry out skin and make you dizzy, especially in a concentrated salt bath. Around 37 to 40 degrees Celsius (roughly 98 to 104 Fahrenheit) is the comfortable range most people settle on.
- Soak time: Fifteen to twenty minutes is enough. Longer soaks don’t deliver more benefit and can leave skin feeling pruney and dried out, especially with the alkaline push from the baking soda.
- Rinse after: A quick shower rinse afterward washes off the salt residue, which can be drying if left on skin. This is more important if you’ve used a heavy Epsom salt concentration.
- Essential oils: If you’re adding essential oils (lavender, eucalyptus, and peppermint are popular), mix them with a carrier oil first rather than dropping them directly onto the salt. Oil and water don’t mix, and undiluted essential oils can irritate skin.
Bath Bombs and DIY Formulations
The fizzy bath bomb you find at any gift shop is, at its core, baking soda and citric acid packed together with binders and fragrance. When dropped in water, the acid and bicarbonate react to release carbon dioxide gas, which is the fizz. Epsom salt is a common addition because it adds weight, helps the bomb hold together during pressing, and contributes the “spa” element marketers love. The citric acid component also means these formulations typically push the bath water toward a lower pH than a plain baking-soda-and-Epsom-salt mix would, which is gentler on the skin barrier.
If you’re making your own bath bombs at home, keep the mixture completely dry until you’re ready to use it. Even a small amount of humidity during storage can start the acid-base reaction prematurely, leaving you with a crumbly, less fizzy product. Store finished bombs in airtight containers with a silica gel packet if your house tends toward humidity. The shelf life of a dry Epsom salt and baking soda mixture, without citric acid, is essentially indefinite. Both are stable crystalline salts that don’t degrade under normal storage conditions.
Using the Mixture in the Garden
This is where mixing the two ingredients deserves more caution. Epsom salt is a popular garden supplement because magnesium is a component of chlorophyll, and sulfur plays a role in plant enzyme systems. Gardeners dissolve it in water and spray it on tomatoes, peppers, and roses. Baking soda, separately, is sometimes sprayed on plants as a folk fungicide, with the idea that its alkalinity discourages fungal growth on leaves.
Mixing the two together for garden use sounds like a logical two-for-one, but the baking soda side carries real risks for soil. Research on the effects of sodium bicarbonate on soil properties found that adding it raised soil pH dramatically (from 7.78 to 9.35 in the study), spiked electrical conductivity and sodium levels, and disrupted the sodium-to-potassium ratio in rice plants, pushing sodium concentrations up fourfold while cutting potassium in half.7Journal of Agricultural Research. NOXIOUS IMPACT OF SODIUM BICARBONATE (NaHCO3 ) ON SOIL PROPERTIES AND IONIC COMPOSITION OF RICE PLANTS Potassium is essential for plant health, and sodium is toxic to most crops at elevated levels. The study used higher concentrations than a casual gardener might, but the direction of the effect is clear: sodium bicarbonate is not a benign soil amendment.
Occasional foliar sprays of diluted baking soda, where the solution lands on leaves and mostly evaporates rather than soaking into the root zone, are unlikely to cause the kind of soil damage seen in that research. But routinely pouring a baking-soda-and-Epsom-salt mix onto garden beds could gradually raise soil pH and sodium levels beyond what your plants can tolerate. If you want the magnesium benefits of Epsom salt for your garden, use it on its own, dissolved in water, and apply it at modest rates. Keep the baking soda for the bathtub.
Common Misconceptions Worth Clearing Up
One persistent myth is that mixing Epsom salt and baking soda creates a “detox bath” that pulls toxins out through the skin. Your liver and kidneys handle detoxification. A warm salt bath can make you sweat, and sweat contains trace amounts of waste products, but the volume is negligible compared to what your organs process continuously. There’s nothing about the combination of magnesium sulfate and sodium bicarbonate that enhances toxin removal. The bath feels good, relaxes muscles, and softens skin. That’s plenty of reason to take one without needing to invoke detoxification.
Another misconception is that the combination “balances” your body’s magnesium and sodium levels. As noted above, transdermal magnesium absorption from a bath is not supported by the current evidence.5PubMed Central. Myth or Reality-Transdermal Magnesium? And sodium from baking soda in bath water does not enter your bloodstream through your skin in any meaningful quantity either. If you’re genuinely low in magnesium, oral supplements or dietary changes are the evidence-based route. A bath is a bath, not a mineral delivery system.
A third misconception applies to cleaning. Some people use an Epsom salt and baking soda paste to scrub bathtubs, tiles, or grout. This works fine as a mild abrasive, but the combination isn’t doing anything chemically special for cleaning purposes. The baking soda is the active ingredient here. It’s a gentle abrasive with mild alkalinity that helps lift soap scum and grease. Epsom salt adds grit. You could substitute table salt or any other crystalline substance and get the same scrubbing effect. If you have the Epsom salt on hand anyway, there’s no harm in using it, but buying it specifically as a cleaning agent is an unnecessary expense.
Who Should Be Cautious
For most people, an Epsom salt and baking soda bath is about as risky as a warm shower. But a few groups should think twice or adjust their approach:
- People with kidney disease: Impaired kidneys have trouble handling excess magnesium. While transdermal absorption is minimal, heavily concentrated Epsom salt baths combined with any cuts or broken skin could theoretically increase exposure. If your kidney function is compromised, check with your doctor before making concentrated salt baths a regular habit.
- People with open wounds or burns: Both salts can sting on broken skin. Baking soda’s alkalinity can also slow wound healing in some contexts. Skip the soak or keep the concentration very low if you have significant skin damage.
- People with very dry or eczema-prone skin: The alkaline push from baking soda can aggravate barrier dysfunction. If you still want the soak, favor Epsom salt and minimize the baking soda, or add citric acid to offset the pH shift.
- Pregnant individuals: Warm baths are generally fine during pregnancy, but very hot baths are not recommended because of the risk of raising core body temperature. Keep the water temperature moderate and the soak time short.
Children can use Epsom salt and baking soda baths too, but in smaller amounts. A quarter to half cup of Epsom salt in a child-sized tub is plenty, with just a tablespoon or so of baking soda. The same rinse-after advice applies, and keeping the water warm rather than hot matters even more for small bodies that heat up faster.
Shelf Life and Storage
Both Epsom salt and baking soda are cheap, shelf-stable, and widely available. You can pre-mix them in bulk and store the dry blend in a sealed container for months without any degradation. The key enemy is moisture. Epsom salt is hygroscopic, meaning it pulls water from the air and can clump. Baking soda does the same, though less aggressively. A tightly sealed glass jar or zip-top bag with the air pressed out keeps either one free-flowing for a year or more. If you’ve added citric acid for a bath bomb blend, moisture is a bigger concern because it can trigger the fizz reaction during storage, so an airtight container becomes essential rather than optional.
Both ingredients are food-grade at the versions sold in grocery stores, which means they meet safety standards well above what you need for bathing. Pharmaceutical-grade Epsom salt (sold at pharmacies) is the same compound, just with tighter purity testing. For bath use, the grocery store version works identically and costs less.