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The one published attempt to make Epsom salt an insecticide was refuted the same year it appeared.

How To Use Epsom Salt To Kill Roaches (And Why It Doesn't Work)

Epsom salt does not kill roaches. Where the claim came from, why the dehydration explanation is chemically wrong, and what to use instead.

13 min read

There is no evidence that Epsom salt kills cockroaches, and the usual explanation for how it would work is chemically backwards. Epsom salt is magnesium sulfate heptahydrate, the saline laxative sold under OTC drug facts labeling, and in mammals it works by pulling water into the gut, which is why the label tells you to dissolve it and drink a full glass of water with the dose. It is not a desiccant, it is not on EPA's list of active ingredients allowed in minimum-risk pesticide products (ordinary table salt is; magnesium sulfate is not), and we could find no published study testing it against any cockroach species. What does work is the boring, well-documented combination UC IPM describes: sanitation, exclusion, monitoring traps, and slow-acting bait placed where roaches harbor.

The earlier version of this article told readers to mix Epsom salt with sugar one-to-one, sprinkle it along baseboards, and expect a population decline in three to six weeks. That advice was unsourced, the stated mechanism ("the epsom salt dehydrates them") is not how magnesium sulfate behaves, and the sugar half of the recipe actively works against you. This version replaces it.

Where The Epsom Salt Idea Came From

This is not a recent internet invention. It traces to a single item in Science in April 1937, in which Hubert and Mable Frings of the University of Oklahoma reported magnesium sulfate as a new insecticide. Contemporaneous press coverage described their bait as bran, molasses, Epsom salt, and enough water to moisten it, aimed at grasshoppers, and quoted their claim that it was as effective as the standard 5 percent arsenic bait while being harmless to livestock.

It did not hold up. Two replies appeared in Science within months, and both carried their conclusions in the titles. Roger C. Smith of the Kansas Agricultural Experiment Station published "Magnesium sulfate: an unsatisfactory substitute for arsenicals in grasshopper baits" (Science 86(2227): 226-228), and N. F. Howard published "Magnesium sulfate valueless as a control for the bean beetle" (Science 86(2230): 286-287). Both citations are indexed in Washington State University's bibliography of the Epsom salt literature, maintained by Linda Chalker-Scott. The original articles are behind a publisher paywall, so we are relying on the citations and titles rather than the full texts.

Two things follow. First, the idea was tested by agricultural entomologists and abandoned nearly ninety years ago. Second, nothing in that episode involved cockroaches at all. The insects were grasshoppers and Mexican bean beetles. The transfer from "1937 grasshopper bait" to "sprinkle it behind your fridge for roaches" happened entirely in blog posts.

Why The Dehydration Explanation Is Wrong

The popular version of the claim is that Epsom salt dries roaches out. Three problems with that.

Epsom salt is already saturated with water. The crystals in the bag are magnesium sulfate heptahydrate, meaning each formula unit is bound to seven water molecules. The anhydrous form of magnesium sulfate is a laboratory drying agent; the hydrated form you buy at a pharmacy is the product of that process, not the reagent. It has no meaningful capacity left to absorb water from anything, including an insect.

Actual desiccant dusts work by a different mechanism entirely. Diatomaceous earth and silica aerogel do not dry insects by osmosis. They strip the waxy outer layer of the cuticle. UC IPM describes silica aerogel as a material that "absorbs waxes from the surface of insects, resulting in their desiccation." NPIC says diatomaceous earth "causes insects to dry out and die by absorbing the oils and fats from the cuticle of the insect's exoskeleton," helped by abrasive edges, and that it stays effective only "as long as it is kept dry and undisturbed." Epsom salt crystals are soluble, blunt, and non-absorptive. They are the wrong material for that job in every respect. If you want the desiccant approach, use diatomaceous earth applied correctly, in thin films inside voids rather than in visible piles.

The laxative mechanism does not transfer to insects. In mammals, magnesium sulfate is an osmotic agent that draws water into the intestinal lumen. That is a whole-body dehydration risk only in the sense of losing fluid through diarrhea, over hours, in an animal drinking a glass of water alongside the dose. Cockroaches do not have that plumbing, and the amount a roach would have to eat is not a number anyone has measured, because nobody has run the experiment. The same reasoning failure sits behind the table salt version of this myth, which we cover in what salt actually does to roaches.

Why The Sugar Half Of The Recipe Backfires

Every version of the Epsom salt recipe pairs it with sugar as an attractant. That part deserves its own objection.

German cockroaches in many populations will not eat glucose. Wada-Katsumata, Silverman, and Schal showed in Science in 2013 that in glucose-averse roaches, glucose stimulates bitter-taste neurons instead of sugar-taste neurons. As Coby Schal put it in NC State's summary of the work, the insect will "close its mouth and run away from glucose in tests." A 2023 follow-up in the *Journal of Economic Entomology* reports that glucose aversion "has been found in cockroach populations worldwide," is a partially dominant inherited trait that spreads under bait pressure, and measurably reduces the secondary kill from baits containing glucose, sucrose, or maltose.

So the attractant half of the recipe is the same ingredient the commercial bait industry has been engineering out of its products. If the population in your kitchen is glucose-averse, a sugar pile is not bait. It is just a sugar pile.

And a sugar pile has costs. Roaches in a clean, competing-food-free environment are far more likely to take a real bait; Texas A&M AgriLife Extension notes that baits "are most effective when few food alternatives are available." Scattering table sugar around the kitchen does the opposite. It also draws ants, and it feeds the very insects you are trying to starve. Our guide to what attracts roaches and how to remove each attractant covers why residue management matters more than any single product.

What Sprinkling Epsom Salt Actually Does

Practically speaking, a line of Epsom salt along a baseboard produces three outcomes, none of them useful.

  • It gets avoided. Texas A&M's guidance on insecticide dusts applies to any visible powder: "Cockroaches will avoid heavy dust deposits." Dusts are meant to be applied so lightly that residues are "barely visible," puffed into voids. A visible white line is something a roach walks around.
  • It attracts moisture and cakes. Epsom salt dissolves readily in water. Under a sink or behind a dishwasher, which is exactly where people are told to put it, it turns into a damp crust.
  • It delays real treatment. This is the actual harm. A German cockroach population compounds fast, and weeks spent on a recipe that does nothing are weeks the population spends growing. Rutgers notes that a female produces 5 to 8 egg cases over her life, totaling roughly 200 to 250 eggs, and that an active infestation runs about 80 percent nymphs.

There is also a mild household-safety point. Epsom salt is an oral laxative, and the DailyMed label warns against use by people with kidney disease or on a magnesium-restricted diet, and tells parents to consult a doctor for children under six. A pet or toddler that eats a sugared pile of it off the floor is unlikely to be seriously hurt, but the likely outcome is vomiting and diarrhea, and it is an entirely avoidable mess. If low-risk products are the reason Epsom salt appealed to you, our risk-based look at pet-safe roach control covers the options that also work.

What To Do Instead

The extension consensus is remarkably consistent across states, and none of it requires exotic products.

  1. Find out where they are before you treat. Put numbered sticky traps at floor-to-wall junctions, under the sink, behind the refrigerator and range, and near the dishwasher. UC IPM says to check them daily for several days, and that roaches are often caught within the first 24 hours. Rutgers adds a specific trick: a small piece of bread dampened with beer in the center of the trap "will significantly increase the effectiveness."
  2. Remove the competing food and water. Store food in sealed containers, take trash out daily, do not leave pet food down overnight, and degrease the sides and back of the range. Fix drips. Penn State Extension's cockroach IPM guidance puts food, water, and harborage removal first for a reason. Oriental cockroaches, per Penn State, can live a month without food if water is available but die within two weeks without water, which is why plumbing leaks matter more than crumbs.
  3. Use gel bait, placed in many small dots. UC IPM calls bait products "the primary pesticides used to treat cockroach infestations," with abamectin, fipronil, indoxacarb, hydramethylnon, clothianidin, imidacloprid, and boric acid among the available actives. Texas A&M advises at least one placement within 1 to 2 feet of every suspected harborage, and notes that "many small, pea-sized placements are more effective than fewer, larger ones." Rutgers estimates a typical one-bedroom apartment may need 10 to 30 grams of gel.
  4. Add a dust only in voids. Boric acid is a genuine cockroach insecticide with an oral and contact mode of action. NPIC explains that it "disrupts their stomach and can affect their nervous system" and "can also scratch and damage the exterior of insects." Apply it inside wall voids, under the dishwasher, and behind the refrigerator, not on countertops or shelves. Expect it to be slow; UC IPM says it "may be 7 days or more before it has a significant effect." Our guide to what to mix with boric acid, and what not to covers the DIY bait question honestly.
  5. Seal the harborage. Caulk cracks along countertops and baseboards, seal plumbing penetrations, fit door sweeps. Penn State specifies silicone caulk, screening, and copper mesh around cabinets, backsplashes, pipes, wires, and cables.
  6. Give it time, then change the active ingredient. Baits are deliberately slow so foragers carry the dose back to the harborage. UC IPM says results may take 7 days or longer. Texas A&M says that if a bait has not controlled the population in 2 to 3 weeks, switch to a bait with a different active ingredient. Penn State uses a 30-day threshold for the same decision.

The full sequence, in order, is laid out in our step-by-step plan for getting rid of roaches.

What Not To Do

  • Do not use foggers or total-release aerosols. UC IPM: "Avoid using foggers, bombs, or aerosol sprays," which "can be hazardous and may repel and disperse cockroaches." Rutgers is blunter, noting they "are ineffective at eliminating cockroach infestations" and "can present a fire hazard." Texas A&M notes they do not penetrate the cracks where roaches actually live.
  • Do not spray around your bait. Texas A&M warns to avoid applying dusts or sprays close to bait placements, "because cockroaches will avoid contaminated baits." Repellent sprays and baits work against each other.
  • Do not buy a product making pest-control claims with no EPA registration number. EPA's consumer guidance is to look for an EPA registration number and a list of active ingredients, and warns that unregistered products "have not undergone the strict safety testing we require." Mixing Epsom salt in your own kitchen is not illegal, but it is worth understanding why: nobody ever had to show a regulator that it works.
  • Do not rely on electronic repellers. Rutgers states plainly that they lack scientific support.

When To Call a Professional

Bring in a licensed operator when any of these are true.

  • You live in an apartment or attached housing. Roaches move between units through shared walls and plumbing chases, and unilateral treatment rarely holds.
  • You are still catching roaches on traps after 30 days of correct baiting with two different active ingredients.
  • Someone in the home has asthma. Cockroach harborages are a significant indoor allergen source, and both UC IPM and Texas A&M recommend HEPA-filtered vacuums specifically for that reason.
  • You are seeing roaches in daylight, in multiple rooms, which generally means the population has outgrown its harborage.

Frequently Asked Questions

Does Epsom salt kill roaches at all?

There is no published evidence that it does. The only serious attempt to use magnesium sulfate as an insecticide, in 1937, targeted grasshoppers and bean beetles and was refuted in the same journal within months. We found no study testing it on any cockroach species, and magnesium sulfate is not an active ingredient in any registered cockroach product.

Will Epsom salt at least repel roaches?

Nothing in the literature supports that either. Repellency has been measured for a handful of plant essential oil constituents, but not for magnesium sulfate. In practice, a visible crystal deposit is more likely to be walked around than avoided as a territory.

Is Epsom salt safer than boric acid?

As something to swallow, yes, marginally; both are low in acute toxicity, and Epsom salt is sold as an oral laxative. But safety only matters relative to effectiveness. Boric acid is a documented cockroach insecticide with a defined mode of action and a label that tells you where it may and may not be applied. Applying a product that does nothing is not the safer choice if the infestation continues.

What about mixing Epsom salt with baking soda, or with borax?

Baking soda has the same evidentiary problem as Epsom salt. Borax and boric acid are different chemicals, and boric acid is the one with the pest-control record. Adding an inert ingredient to a working one mostly dilutes it, and any homemade mixture using a product off its label is outside the directions the manufacturer tested.

How long should I wait before deciding a treatment failed?

Two to four weeks, with traps in place so you are measuring rather than guessing. Texas A&M's threshold is 2 to 3 weeks before switching active ingredients; Penn State's is 30 days. If trap counts are flat or rising at that point, change the product or call a pro.

If my kitchen is clean, why do I still have roaches?

Cleanliness reduces the food supply, but it does not seal the building or remove the harborage. German cockroaches arrive in grocery bags, appliances, cardboard, and secondhand furniture, and they persist on grease films and moisture rather than visible crumbs. Sanitation makes bait work better; it does not substitute for it.

Does Epsom salt work outdoors or in the garden against roaches?

No. The historical work on magnesium sulfate in agriculture is almost entirely about correcting magnesium deficiency in crops, not about killing insects. The WSU bibliography on Epsom salts is mostly plant-nutrition literature, with the two 1937 refutations as the only substantial insecticide entries.

Sources

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