Diatomaceous earth is a naturally occurring powder made from the fossilized remains of tiny aquatic organisms called diatoms. It contains between 68% and 96% silica, and its unique porous structure makes it useful for a surprisingly wide range of purposes: pest control, industrial filtration, liquid absorption, gardening, and even cosmetics. The specific grade matters enormously, though, because different processing methods produce very different products with very different safety profiles.
Food-Grade vs. Pool-Grade: A Critical Distinction
Diatomaceous earth comes in two main forms, and they are not interchangeable. Food-grade diatomaceous earth is minimally processed and contains very low levels of crystalline silica, typically around 0.1% to 4%. The FDA classifies food-grade diatomaceous earth as “generally recognized as safe” (GRAS), and it appears in multiple food-processing regulations.
Pool-grade (also called calcined) diatomaceous earth has been heated above 1,800°F, which converts much of the harmless amorphous silica into crystalline silica in the form of cristobalite. Calcined products can contain anywhere from 1% to 75% cristobalite. This form is used strictly for industrial filtration, like swimming pool filters, and should never be used around food, pets, or gardens.
Pest Control Without Chemicals
The most popular home use for food-grade diatomaceous earth is killing insects. It works through a purely physical mechanism rather than a chemical one. When insects crawl through the fine powder, the microscopic particles increase the permeability of their waxy outer coating. This causes both cuticular and respiratory water loss to spike, essentially dehydrating the insect from the outside in. Scanning electron microscopy has confirmed that the particles absorb the lipid layer on insect exoskeletons, stripping away the barrier that normally keeps moisture locked inside.
Because the mechanism is physical, insects can’t develop resistance to it the way they can with chemical pesticides. It’s effective against ants, bed bugs, cockroaches, fleas, silverfish, and many other crawling insects. The tradeoff is speed: it typically takes 24 to 72 hours to kill insects, and it only works when the powder is dry. Rain, heavy dew, or even high humidity can render it ineffective until it dries out again.
Using It in Your Home
For indoor pest control, apply a thin, even layer along baseboards, under furniture, on carpets, and in cracks where insects travel. You can leave it on carpet for up to three days before vacuuming soft surfaces and wiping down hard ones. A thick pile won’t work better. Insects will simply walk around a visible mound, so dust it lightly enough that it’s barely visible.
Using It in the Garden
Outdoors, you can apply diatomaceous earth as a dry dusting directly on plants and soil or mix it into a liquid spray at roughly four tablespoons per gallon of water. The liquid method coats surfaces more evenly, but it only works once the water evaporates and the powder dries. For active infestations, reapply weekly for about a month. For maintenance, every three to four weeks during pest season is enough. Wind and rain wash it away faster outdoors, so you’ll need more product and more frequent applications than you would indoors.
One important caveat: diatomaceous earth is non-selective. It will harm beneficial insects like bees and ladybugs just as readily as pests. Avoid applying it directly to flowers or anywhere pollinators are active.
Flea Control Around Pets
Many pet owners turn to diatomaceous earth as a chemical-free flea treatment, but it requires some caution. While food-grade diatomaceous earth is considered nontoxic if ingested in small amounts, the fine dust can irritate eyes, skin, and the respiratory system of dogs and cats. The American Kennel Club advises against applying it directly onto a dog’s skin or spreading it loosely inside your home where pets might roll in it, inhale it, or ingest it while grooming.
A safer approach is adding it to soil in outdoor areas where your pet spends time, while keeping the pet away from the treated zone until the dust settles. Indoors, applying it to carpets and baseboards in rooms the pet doesn’t access, then vacuuming thoroughly before letting them back in, reduces exposure risk.
Industrial Filtration and Absorption
Outside the home, diatomaceous earth is a workhorse material in commercial filtration. Its porous, microscopic structure traps particles as small as one micron while allowing liquid to pass through. Breweries and wineries use it to clarify beer and wine. Juice manufacturers filter through it to remove pulp and sediment. It also plays a role in pharmaceutical production, edible oil processing, wastewater treatment, and fuel purification across the oil and gas industry.
The absorption capacity of diatomaceous earth is equally impressive. Raw diatomite can absorb 100% of its own weight in oil-based substances, and heat-treated forms can absorb over 200% of their weight. This makes it a go-to material for cleaning up chemical spills, soaking up oil in industrial settings, and managing hazardous liquid waste. You’ll also find it in cat litter, where its absorbency and odor-trapping properties are put to everyday use.
Health Supplement Claims
Food-grade diatomaceous earth has gained popularity as a dietary supplement, with sellers claiming it lowers cholesterol, strengthens bones, removes heavy metals, and “detoxifies” the body. The scientific evidence behind these claims is thin. A small number of studies have suggested a cholesterol-lowering effect, but they were poorly controlled. Researchers couldn’t determine whether silica was responsible or whether participants’ diets played a role.
The detoxification claim rests on even shakier ground. Your liver, kidneys, and digestive system already remove waste products continuously. There is no credible evidence that your body accumulates toxins that require a special substance to flush out.
Some people also take it as a source of trace silica, which does play a role in connective tissue and bone health. But most people get adequate silica from food, and no clinical trials have demonstrated that supplementing with diatomaceous earth improves bone density or joint health in any measurable way.
Safety Precautions Worth Taking
Even food-grade diatomaceous earth poses a real respiratory hazard if you breathe in the dust. The National Institute for Occupational Safety and Health sets the recommended exposure limit at 6 milligrams per cubic meter of air over a 10-hour period. Uncalcined (food-grade) diatomaceous earth is classified as a nuisance dust rather than a carcinogen, but chronic inhalation of any fine silica particles can irritate the lungs over time.
Whenever you’re applying it, wear a dust mask or respirator, especially indoors. Protective eyewear is also a good idea, since the powder dries out mucous membranes on contact. Keep the area well ventilated, and avoid creating clouds of dust by applying it gently rather than shaking it out vigorously. If you have asthma or any chronic lung condition, take extra care or have someone else handle the application.
The calcined, pool-grade version carries significantly higher risks. Crystalline silica is a known lung carcinogen with long-term exposure, which is why pool-grade diatomaceous earth should only be used in enclosed filtration systems, never spread around your home, yard, or anywhere people and animals breathe.