How desiccant dusts work
A desiccant dust damages the thin waxy layer on an insect's outer shell. The insect then loses water and dies. Silica gel and diatomaceous earth both work this way.
Because the action is physical, the dusts can still work on bugs that resist sprays. In one laboratory study, label-rate doses of two dusts killed every bug in a highly pyrethroid-resistant strain. One was silica gel and the other was diatomaceous earth. The silica gel took three to four days, while the diatomaceous earth took 14 days.
That gap matters when you plan around treatment resistance. A slow dust can still help, but you must wait for it to work.
Silica gel and diatomaceous earth are not the same
Researchers compared eight dust products in the laboratory. Silica gel killed 100% of bed bugs in all three exposure tests. In the brief-exposure test, the diatomaceous earth products and the pyrethroid dusts killed 65% or fewer.
However, these are laboratory figures for particular products. A real home has deep cracks, clutter and people living in it. Use the results to compare products, not to promise an outcome.
Dose also matters. At sub-label rates, a resistant strain survived 50% longer on silica gel than a susceptible one. The authors suggest a thicker cuticle may play a part. So under-dosing is a poor idea.
Check the product before you buy
In Great Britain, the HSE publishes lists of authorised biocidal products. A product missing from the list is not automatically banned, because some active substances are still under review. Even so, choose a product that suits the job, and check the label before you buy.
Members of the public should only use products meant for the general public. Professional-only products need trained users. Pool, food-grade and industrial powders are not the same as a labelled bed bug dust.
The US EPA warns that pool or food-grade diatomaceous earth can harm you when you breathe it in. Read the label before you buy and again before you use it.
Where dust fits in a plan
Dust is a slow, dry tool, so it suits some jobs better than others. It leaves a residue that bugs must cross, which fits cracks and edges they use. It does not suit a heavy infestation that needs fast action.
Therefore most plans pair it with a quicker method. For example, steam or heat can deal with bugs you can reach now. The dust then covers gaps for the days after. Our steam treatment guide and treatment comparison show how the options differ.
Place it thinly and safely
Follow the label rate and the label placement. Do not add extra to make it stronger. Heavy layers also create airborne dust and visible mess.
Diatomaceous earth can irritate the nose, eyes and skin. Breathing in a large amount can cause coughing and shortness of breath. Because of this, avoid raising dust and wear the protection the label asks for.
Keep the product in its original container, out of reach of children and pets. Do not put dust on sleeping surfaces or bedding unless the label allows it. If you are unsure, ask for a professional inspection first.
Judge results slowly
Dust is not instant. Laboratory kills took three to 14 days, and field results depend on contact. So you need monitoring, not a quick look.
Keep a room-by-room log of sightings and bites. Interceptor traps under bed legs can help you see change. Our post on how long bugs take to die after treatment explains what to expect. Another post shows the signs a treatment has worked.
If activity continues, ask for an inspection. Dust works best as one part of a plan, alongside insecticide choices and heat treatment where they suit the home. For powders sold for home use, read our post on diatomaceous earth at home.
Sources and further checks
Open each source before you act on anything that can change, such as council services, prices, tenancy rules and product labels. Labels and official guidance are revised from time to time, so the source always wins over our summary.