Does Diatomaceous Earth Work? What the Testing Shows
Diatomaceous earth does kill insects, but roughly nine times slower than the silica gel dust sold beside it: in a controlled bed bug comparison, silica gel killed half the insects in 20 hours and diatomaceous earth took nearly eight days. In a more realistic test where bugs merely crossed a treated band once, silica gel killed 95 per cent within a day while diatomaceous earth and six other dusts killed under 40 per cent. It also works by drying insects out, so humidity works directly against it, and supermarket-grade product performed worst of all.
Diatomaceous earth occupies a strange position: recommended by people who distrust pesticides, sold as a pesticide, and genuinely effective under conditions that rarely exist in a real building. The evidence is unusually good for a product of this kind, and it does not say what either side claims.
What it actually does to an insect
The popular explanation is that the fossilised diatom fragments are microscopic glass shards that cut the insect open. The best instrumented study says otherwise. A 2024 paper used open-flow respirometry and electron microscopy on flour beetles and found diatomaceous earth significantly increased the permeability of the cuticle and the rate of water loss, while the physical damage to the cuticle surface showed only a non-significant tendency to increase.
In other words it is a desiccant. It strips the waxy layer that keeps an insect from drying out, and the insect dies of dehydration. The EPA’s own 1991 review describes these products as abrasive and acting as desiccants; the more recent measurement weights it firmly toward desiccation.
That single fact explains everything else, including why it is slow, why humidity ruins it, and why it cannot be the fast knockdown people expect.
The comparison that matters
Diatomaceous earth is almost always used where a synthetic amorphous silica gel dust could be used instead. The two look identical and are marketed in similar language. They do not perform alike.
| Silica gel dust | Diatomaceous earth | |
|---|---|---|
| Time to kill half the bed bugs | 20 hours | 7.4 to 8.1 days |
| Time to 100 per cent mortality | 3 to 4 days | 14 days |
| Brief exposure, mortality at 1 day | 95% | Under 40% |
| Horizontal transfer between insects | Demonstrated | Not demonstrated |
| Repellency | Low | Measurable; bugs avoid crossing |
Continuous exposure figures from Lilly and colleagues, 2016. Brief exposure figures from Singh and colleagues at Rutgers, 2016, where insects crossed a 2.5 cm treated band once.
The brief-exposure result is the one to weigh. The Rutgers authors state plainly that forced-exposure assays “can result in inflated mortality”, because in a real room an insect crosses a treated band and walks on rather than sitting in the dust for days. Under that realistic test, diatomaceous earth and six other dusts all came in under 40 per cent while the silica gel reached 95 per cent in a day.
Its measurable repellency compounds the problem. A dust that insects prefer to walk around delivers less of itself than one they cross without noticing.
Humidity is the hidden variable
A product that kills by dehydration works badly in damp air, and the effect has been measured. Work at the USDA found mortality within each temperature decreased as humidity rose, and at 22 degrees Celsius with 57 and 75 per cent relative humidity nearly all the test beetles survived. A 2025 study found the best result always at 30 degrees and 40 per cent humidity, and the worst always at 25 degrees and 60 per cent.
Ageing matters too. Fresh silica gel killed 99 per cent of bed bugs by day 10; after a month in place it managed 81 per cent at 52 per cent humidity, 79 per cent at 75 per cent, and 56 per cent at saturation. Diatomaceous earth, being the weaker desiccant, degrades at least as much.
A commonly cited threshold is that performance collapses above roughly 70 to 75 per cent relative humidity. That figure traces to a 1998 review rather than a single experiment, and not every study finds a humidity effect, so it is best treated as a rule of thumb. The direction is not in doubt.
The practical consequence: the damp basement, crawlspace and under-sink locations where people most want to use this product are the locations where it performs worst. Our page on the moisture pests covers why those areas need the water fixed first regardless.
Grade matters, and one grade is a health hazard
Pool-grade diatomaceous earth is heat-treated, which converts much of the silica to a crystalline form. Crystalline silica is associated with silicosis and lung cancer; the amorphous form used in pesticide products is not, and the International Agency for Research on Cancer found inadequate evidence for its carcinogenicity.
The EPA’s bed bug guidance is explicit that pool or food grade diatomaceous earth should not be used for pest control because it can harm you when breathed in, and that the pesticide version uses a different diatom particle size. Use only an EPA-registered product, and follow the label, which for dusts generally requires a dust mask during prolonged application.
We could not verify the specific crystalline silica percentages that circulate for pool and food grade, which appear only in supplier material rather than in any government or university source. The hazard direction is well established; the exact numbers you see quoted are not.
One more finding worth stating plainly. A 2024 study comparing professional and supermarket product found professional-grade diatomaceous earth reached 100 per cent mortality by day two to four under permanent exposure, while supermarket-grade managed under 20 per cent.
Where it is a reasonable choice
- Dry, undisturbed voids. Wall voids, under appliances, behind cover plates: dry, protected, and somewhere a fine dust can sit for months without being cleaned away.
- Where a long game is acceptable. It does not do knockdown. If the problem needs solving this week, this is the wrong product.
- Applied as a barely visible film. The commonest application error is a thick white line, which insects walk around. A light dusting they cross unaware delivers more product.
- Not in damp areas, where it degrades fastest and is needed most.
- Not as the sole response to bed bugs. On this evidence a silica gel dust is the better desiccant by a wide margin, within a programme rather than alone; see our bed bug treatment guidance.
For ants specifically, be careful what you believe. We could find no peer-reviewed efficacy figure for diatomaceous earth against Argentine, odorous house or carpenter ants; every specific percentage we located traced back to a pest control company’s own blog. The best figure in the literature for any ant is 29 per cent mortality of fire ants after 10 days.
This sits alongside the broader picture in our review of whether natural pest control products work, and our comparison of professional and retail products.
Frequently asked questions
Does diatomaceous earth actually kill bugs?
Yes, but slowly and conditionally. Under continuous laboratory exposure it killed half of a bed bug population in 7.4 to 8.1 days and reached 100 per cent by day 14. Under a realistic brief exposure, where insects cross a treated band once, it killed under 40 per cent in a day while a silica gel dust killed 95 per cent.
How does diatomaceous earth work?
By desiccation, not by cutting. A 2024 study using respirometry and electron microscopy found it significantly increased cuticle permeability and water loss, while physical damage to the cuticle showed only a non-significant increase. It strips the waxy layer that stops an insect drying out, which is why it is slow and why humidity undermines it.
Does humidity stop diatomaceous earth working?
It substantially reduces it. Mortality falls as humidity rises, and in USDA testing nearly all beetles survived at 22 degrees Celsius with 57 to 75 per cent relative humidity. Desiccant dusts also degrade in place: silica gel dropped from 99 per cent effectiveness when fresh to 56 per cent after a month at saturation.
Is diatomaceous earth safe to use indoors?
Use only an EPA-registered pest control product and follow its label, which for dusts generally requires a dust mask during prolonged use. Pool-grade must never be used: heat treatment converts much of the silica to the crystalline form associated with silicosis and lung cancer. The EPA states directly that pool or food grade should not be used for pest control.
Sources
- Lilly, Latham, Webb and Doggett, “Desiccant dusts for the control of bed bugs,” Insects 7(4):74, 2016.
- Singh, Wang, Wang, Cooper and Zha, “Effectiveness of dusts against bed bugs,” Journal of Economic Entomology 109(4), 2016.
- Romei and Schilman, “Diatomaceous earth increases cuticular permeability and water loss,” Pest Management Science 80, 2024.
- Arthur, “Effect of temperature and humidity on diatomaceous earth efficacy,” Journal of Economic Entomology 93(2), 2000.
- Ranabhat and Wang, “Effect of ageing and humidity on desiccant dust performance,” Journal of Economic Entomology 113(4), 2020.
- US Environmental Protection Agency, Reregistration Eligibility Decision 738-F-91-107, silicon dioxide and silica gel, 1991, and EPA bed bug product guidance.
