Diatomaceous earth does not directly kill fungus the way it kills insects. DE works primarily as a desiccant, absorbing moisture from its surroundings, which can create conditions less favorable for fungal growth. But it lacks true antifungal properties on its own, and there is no strong scientific evidence that it can eliminate an established fungal infection on surfaces, in soil, or in the body.
How DE Actually Works
Diatomaceous earth is a fine powder made from the fossilized remains of tiny aquatic organisms called diatoms. It contains about 80% to 90% silica. Its claim to fame is killing insects: the microscopic sharp edges of the particles scratch through an insect’s outer coating and absorb the waxy layer that keeps moisture in, causing the insect to dehydrate and die.
Fungi are fundamentally different from insects. Fungal cells have rigid cell walls made of chitin, and many fungi survive as spores that are remarkably resistant to drying out. DE’s physical mode of action, which relies on piercing a soft exoskeleton and pulling out moisture, doesn’t translate well to fungal organisms. Sprinkling DE on mold or fungus won’t destroy it the way a true antifungal solution would.
What DE Can Do Against Fungal Problems
Where DE has genuine value is moisture control. Fungi thrive in damp environments, and DE’s high absorbency can reduce the moisture that fungal colonies need to grow and spread. In this sense, it works as a preventative tool rather than a treatment. If you dust DE in a damp crawl space, along a basement wall, or on the surface of potting soil, it can help keep conditions dry enough to slow fungal colonization.
This distinction matters. Removing moisture doesn’t kill existing mold or fungal infections. It just makes the environment less hospitable for new growth. University extension services note that while DE may help remove moisture, cleaning existing mold still requires a direct solution like a half-water, half-vinegar mix. Other desiccant products, like silica gel packs, can serve the same moisture-absorbing role.
DE for Fungus Gnats Is a Different Story
One area where DE genuinely helps with a fungus-related problem is controlling fungus gnats in houseplants. These tiny flies lay eggs in moist topsoil, and their larvae feed on organic matter and plant roots. A layer of DE on the soil surface kills the adult gnats through the same dehydration mechanism it uses on other insects, and it dries out the top layer of soil enough to discourage egg-laying. This is one of the most popular home uses of DE, and it works because the target is an insect, not the fungus itself.
Keep in mind that DE loses its effectiveness when wet. If you water your plants from the top, you’ll need to reapply. Many gardeners switch to bottom-watering while treating a fungus gnat problem so the DE layer stays dry and active.
Lab Research on DE Composites
Some laboratory research has explored whether DE can be chemically modified to fight fungi. A 2021 study published in a peer-reviewed journal found that when DE was combined with zinc oxide to create a micro-composite material, the resulting product did show antifungal activity against Aspergillus fumigatus, a common and sometimes dangerous mold. The composite also boosted the effectiveness of existing prescription antifungal medications.
This is worth noting, but it’s important context: the antifungal activity came from the zinc oxide composite, not from plain DE. The diatomaceous earth served as a framework to deliver and enhance the active ingredient. Ordinary food-grade or garden-grade DE sitting in your pantry does not have these properties.
Safety Considerations
If you decide to use DE for moisture control or insect management, respiratory protection matters. The fine particles can irritate your nose, nasal passages, and lungs if inhaled. Breathing in large amounts can cause coughing and shortness of breath. The crystalline form of DE (used in industrial applications, not the food-grade version) poses a more serious long-term risk: chronic inhalation is associated with silicosis and bronchitis.
Stick with food-grade DE for any home or garden use. Wear a dust mask when applying it, avoid stirring up clouds of powder indoors, and keep it away from children and pets during application. Once it settles, the exposure risk drops significantly.
What Actually Kills Fungus
If you’re dealing with mold on household surfaces, a vinegar solution (equal parts water and white vinegar) or a commercial mold-killing product will do what DE cannot. For fungal infections on plants, copper-based fungicides and neem oil are effective options with well-established track records. Fungal infections on skin or nails require antifungal creams or oral medications.
DE can play a supporting role by keeping surfaces and soil dry, which helps prevent fungal problems from returning after you’ve treated them. Think of it as part of a moisture management strategy rather than a fungus killer. Used alone against an active fungal problem, it simply won’t get the job done.