What the research found
Researchers at Ohio State University tested three over-the-counter foggers on bed bugs from real homes. The bugs showed little or no harm after two hours of direct exposure. However, one population was an exception, with some deaths after five to seven days when bugs sat in the open.
Death rates stayed low whenever the bugs could reach a hiding place. Even a lab strain that is sensitive to pyrethroids survived under a thin layer of cloth. The authors therefore advise against recommending total-release foggers for bed bugs.
Two reasons they miss
The first reason is hiding. In homes, most bed bugs sit in protected sites where the mist does not touch them. A fogger settles broadly, while the bugs sit in cracks and layered materials.
The second reason is resistance. Many bed bugs from real homes resist pyrethroids, and most foggers rely on pyrethroids or pyrethrins. Brief contact with a low dose does not harm those bugs. Our guide to insecticide resistance explains why.
Health and fire risks
A US health report counted 3,222 fogger-related illnesses in ten states between 2007 and 2015. Although most cases were mild, common causes were failing to leave, going back in too soon and using too many units. Coughing and other breathing problems were the most common symptoms.
The US EPA adds that the propellants are usually flammable, so misuse can cause a fire or explosion. It advises one fogger per room at most, with no ignition sources nearby. Everyone, pets included, should leave and stay out for the time on the label. Open the windows on return.
These figures come from the United States, and UK labels differ. Follow the label on your own product. The HSE says you must read and understand it before you use any biocide.
Why a fogger can cost you time
A fogger can delay the real work. You may wait weeks, then find the bugs are still there. Meanwhile you have paid for a product and spent time away from your home.
Prevention matters too. The NHS advises checking luggage and clothing before you bring them in. Our post on avoiding bed bugs after travel covers that risk. Our post on whether shop-bought sprays work looks at other products from the same shelf.
If you have already used one
Do not repeat the treatment out of frustration, because more mist will not reach hidden bugs. The EPA says to use no more foggers than necessary. Ventilate the rooms as the label directs.
Then check for live bugs, fresh blood spots and brown spots on bedding. Because the mist may not reach hiding places, assume the bugs are still there until inspection shows otherwise. If signs continue, move to a directed method.
Write down the product, the date and the rooms you treated. The EPA advises keeping records of locations and dates. A clear record helps anyone you ask for advice, and it shows you whether signs are fading.
Choose directed work instead
Good treatment starts with inspection. Then it puts the method where the evidence points. Heat treatment and steam treatment reach hidden bugs by contact or temperature, while a labelled residual from the insecticides guide can cover cracks that you have mapped.
Although it is slow, a desiccant dust is a dry option. Read our post on diatomaceous earth for bed bugs before you try one. Whatever you pick, check that the label names bed bugs and your type of room.
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.