Diatomaceous earth (DE) has a strong reputation as a natural dewormer, but the scientific evidence is mixed at best. While it reliably kills insects by physically damaging their exoskeletons, its effectiveness against internal parasites like roundworms, hookworms, and tapeworms is far less clear. Most controlled studies in livestock have found no significant reduction in parasite loads, and the FDA has not approved DE as a dewormer for humans or animals.
How Diatomaceous Earth Actually Works
DE is made of fossilized microscopic aquatic organisms called diatoms. Under a microscope, the particles have razor-sharp edges. When insects walk through DE powder, those edges cut into the waxy outer layer of their exoskeleton. The powder then absorbs oils and fats from the insect’s body, causing it to dehydrate and die. This is a purely mechanical process, not a chemical one, which is why DE works as long as it stays dry.
This mechanism is well established for external pests like ants, fleas, bed bugs, and mites. The problem is that internal parasites live in a wet, mucus-lined digestive tract, which is a completely different environment. Worms inside the gut don’t have the same hard exoskeleton that insects do, and the moist conditions may neutralize DE’s drying and abrasive effects before it can do meaningful damage.
What Livestock Studies Actually Found
Researchers have tested DE as a dewormer in sheep, goats, and poultry with inconsistent results. One study in Merino sheep reported a 61% reduction in fecal egg counts when DE was added at 2% of their diet, though the researchers noted that efficacy varied over time. A study in goats, however, found the opposite: over six weeks of daily DE supplementation, fecal egg counts actually increased. The researchers concluded that DE did not support its promoted use as an effective alternative deworming treatment.
In poultry, the picture is slightly more nuanced. A study on free-range laying hens found that DE reduced burdens of specific parasites (Capillaria and Heterakis) in one breed but had no significant effect on a more parasite-resistant breed. This suggests that any benefit may depend heavily on the animal, the parasite species, and the conditions of the study.
Taken together, the livestock research does not consistently support DE as a reliable dewormer. Some studies show modest effects, others show none at all. No study has demonstrated the kind of consistent, high-level parasite reduction you’d expect from a proven treatment.
DE for Dogs, Cats, and Other Pets
Pet owners often turn to DE as a natural alternative to conventional dewormers. Common recommendations suggest mixing about half a teaspoon per 5 kg of body weight into food daily. However, there are no published clinical trials confirming this dosage actually eliminates intestinal worms in dogs or cats. The recommendations circulate largely through pet food companies and online forums rather than veterinary research.
Conventional dewormers target specific parasites with drugs designed to paralyze or starve the worms. DE, by contrast, relies on a physical mechanism that evolved to work on dry-bodied insects in open air. The gut environment where roundworms, hookworms, and tapeworms live is warm, wet, and coated in mucus, conditions that likely blunt whatever abrasive or drying action DE might have.
The FDA’s Position on DE as a Dewormer
The U.S. Food and Drug Administration does not recognize diatomaceous earth as safe and effective for treating parasites in humans. In 2019, the FDA issued a warning letter to a company marketing DE as an “internal de-wormer,” stating that making such claims turns the product into an unapproved drug under federal law. Food-grade DE is approved as an anti-caking agent in animal feed and as an insecticide for stored grain, but not as a treatment for intestinal parasites in any species.
Food Grade vs. Pool Grade
If you do choose to use DE around animals or in your garden, the type matters enormously. Food-grade DE contains less than 1% crystalline silica, the form of silica that causes lung damage. Pool-grade (filter-grade) DE has been heat-treated, which converts much of the silica into its crystalline form. Pool-grade DE is toxic if ingested and should never be used around animals, in gardens, or anywhere near food.
Food-grade products must also meet limits for heavy metals: no more than 10 mg/kg of arsenic and 10 mg/kg of lead. Always check the label to confirm you’re using a food-grade product if it will come into contact with animals, soil, or anything edible.
Will DE Harm Earthworms in Your Garden?
If your search was about garden worms rather than parasites, the news is better. Food-grade DE does not appear to harm earthworms. Unlike insects, earthworms lack a hard exoskeleton and can actually digest the amorphous silica particles, passing them out in their castings. Earthworm farmers routinely use food-grade DE in worm beds to control fungus gnats and other pests without harming the worms themselves. Pool-grade DE, however, contains crystalline silica and added chemicals that can kill earthworms, so it should never be used in garden soil.
Handling DE Safely
Even food-grade DE poses a real inhalation risk. The fine dust irritates the eyes and respiratory tract, and prolonged exposure can contribute to a lung condition called pneumoconiosis. When applying DE, wear a dust mask rated N95 or higher and eye protection. Work in well-ventilated areas and avoid creating dust clouds. Keep pets and children away from dry DE powder until it has settled into soil or bedding.
DE is most effective as an insecticide when applied in thin, dry layers in cracks, along baseboards, or dusted onto animal bedding to target fleas and mites. For these external pest uses, the evidence is solid. For internal parasites, the science simply hasn’t caught up with the marketing claims, and relying on DE as your only deworming strategy risks leaving a real parasite infection untreated.