The can says "kills on contact," the ants are on the counter, and the instinct is to spray the counter. That is the one place the label tells you not to, and it is a fair summary of how most indoor spraying goes wrong: the right product, put where the insect was seen rather than where it lives.
Spray where insects travel and hide, not where you saw one: the crack where the baseboard meets the floor, the gap under the sink around the pipes, the hinge side of cabinets, door thresholds and window frames. A thin band into those gaps does more than a wet floor.
Never spray food surfaces, mattresses or bedding unless the label names bed bugs, whole rooms, or anywhere near bait. For ants and cockroaches the EPA's own advice is baits first, and a spray is often the wrong tool entirely. This page is about what you can buy and use yourself. What a professional treatment covers is a separate question.
Before You Spray: The Label Is the Law
Every pesticide sold in the United States carries the same sentence: it is a violation of federal law to use the product in a manner inconsistent with its labeling. The EPA's household guidance is built on that, and it is short enough to quote. Always read and follow the pesticide label's instructions and safety warnings. Don't use outdoor chemicals indoors. Don't assume that twice as much is better. Keep pets and children away from areas where pesticides have been applied. Store pesticides in their original containers.
Two of those matter more than people expect. Outdoor concentrates are formulated to break down in sunlight and rain, so indoors they linger at strengths never tested for a living room, and the EPA's bed bug page says outright that using an outdoor product inside can make your home dangerous and uninhabitable. And "twice as much" is the most common mistake we see in homes that have been sprayed by the homeowner: a soaked baseboard is not more protective than a treated one, it is a larger dose for whoever lives there.
Where to Spray, Room by Room
The principle is crack and crevice. Insects move along edges and rest in gaps, so a narrow band directed into the gap reaches them and stays out of the open where you live. The EPA's household advice asks even for professional treatments to use baits and crack and crevice treatments when feasible, and it applies to your own can just as much.
Kitchen. The gap under the sink where pipes enter the cabinet. The hinge side and back corners of lower cabinets. Behind and beneath the refrigerator and stove, into the gap at the wall, not across the floor in front. Along the baseboard behind the trash can. Never the counter, the inside of a cabinet that holds food or dishes, or any surface a plate touches. Cover or remove food and utensils first.
Bathroom. Under the vanity where the supply and drain lines come through the wall. The floor gap behind the toilet. Where the tub or shower surround meets the wall. The threshold. Bathrooms are small and often poorly ventilated, so a light band and an open door matter more here than anywhere.
Doors and windows. The threshold and the bottom of the door frame on exterior doors, which is the route in for the large outdoor cockroaches, spiders and centipedes. Window frames where they meet the wall, and the sill only if there is a gap. Do not spray screens or glass.
Living rooms and bedrooms. Baseboards behind and beneath furniture, where the wall meets the floor. The gap behind a headboard. Closet floor edges after the contents are out. Not carpet in the open, not upholstery, and not bedding.
Garage, utility and laundry. Where the water heater, washer and dryer connections penetrate the wall, along the slab edge, and around the garage door frame. This is where a lot of what ends up inside is coming from, and it is the one indoor space where a slightly heavier application is reasonable because nobody sleeps there.
Where Never to Spray
Food surfaces and inside food cabinets. Nothing on the label permits it and nothing about it works better.
Mattresses, box springs, pillows and bedding, unless the product is EPA-registered with bed bugs on the label. The EPA's instruction for bed bugs is to buy products labeled for them, read the label completely, and use them where the label says, which for most consumer sprays is cracks and crevices around the bed, not the surface you sleep on. Encasements do more for a mattress than any spray.
Whole rooms. Misting across a floor or a wall puts most of the product where no insect will walk and where you will. It also backfires: researchers found that volatile pyrethroids repel German cockroaches by smell, and UC IPM warns that aerosols and foggers may repel and disperse cockroaches to other areas without actually killing them. Broadcast spraying is how a kitchen problem becomes a house problem.
Anywhere near bait. If you or a technician have put down gel or granular bait, do not spray within reach of it. Clemson's factsheet is direct: spraying a residual insecticide over bait placements makes cockroaches avoid the bait. The spray you added on Saturday undoes the treatment that would have worked by Wednesday.
Where a cat grooms. Permethrin, the residual active in many indoor sprays, is unusually toxic to cats because, in the National Pesticide Information Center's words, it takes their bodies a long time to break it down. Cats walk through a treated baseboard and then lick their feet. Keep cats out until surfaces are fully dry and treat only the gaps, not the floor.
Near pilot lights, ignition sources or into a closed cabinet with any aerosol or fogger. Propellants are flammable, and the EPA's fogger guidance is six feet or more from all ignition sources and never in closets, cabinets or under counters.
When a Spray Is the Wrong Tool
For the two insects people spray most, ants and cockroaches, the EPA's guidance is that after preventive steps have been taken, you can use baits as a first line of chemical defense. The reason is that a spray kills the individuals that touch it and sends the rest away from the smell, while a bait is carried back to the nest and kills the colony. In field testing on German cockroaches, gel baits reduced populations by 70 to 93% within a month; the same research found the pyrethroid in consumer foggers had 202 times less effect than on a susceptible lab strain, and more than 62% of the cockroaches survived fogger treatments in real homes.
So the practical order is: bait for ants and roaches, spray only into the gaps they travel through, and keep the two apart. For the single insect on the wall in front of you, a University of Florida study found a 1% dish soap solution killed 92 to 100% of German cockroaches in a 30-second exposure. It has no label problem, no residue and no fumes, and it is often the better answer than reaching for the can.
How Long an Indoor Spray Lasts
It depends on the active ingredient, and the label will say. Contact sprays, typically pyrethrins, excite the insect's nervous system and cause paralysis quickly, then break down within hours and leave nothing behind. Residual sprays are built to stay. NPIC reports that in a test of permethrin applied indoors near a window, 60% of what was applied was still on the surface after 20 days.
Three things shorten that. Mopping and wiping remove it, which is why a band in the crack outlasts a band on the floor. Direct sunlight degrades it. And porous surfaces such as unsealed wood and concrete absorb it, so the same product lasts longer on a painted baseboard than on a garage slab. Reapply when the label allows, not when you feel like it, and never because you still saw a bug three days later, since insects hatching from egg cases and cocoons appear for two weeks after any treatment.
A Word on Bug Bombs
Total release foggers are the product most often used wrongly indoors, so the EPA publishes specific precautions. Use no more than one fogger per room; a typical 6 oz. can treats an area up to 25 by 25 feet, which is bigger than most rooms in most houses. Place it six feet or farther from all ignition sources, including pilot lights. Do not use them in small, enclosed places such as closets, cabinets, or under counters or tables. Stay out until the time on the label has passed, usually two to four hours, and then open doors and windows to ventilate.
Follow all of that and the fogger still does not reach the cracks and voids where the insects are. Kentucky's extension entomologists put it plainly: very little insecticide actually penetrates into cracks, voids, and other hidden locations where cockroaches and other pests congregate and spend most of their time. It settles on your counters and floors instead. That is why it does not appear anywhere in the room-by-room list above.
| Location | Spray? | What to do instead or as well |
|---|---|---|
| Baseboard crack, behind furniture | Yes, thin band into the gap | Vacuum the edge first |
| Under sink around pipes | Yes | Seal the gap around the pipe afterward |
| Behind fridge and stove | Yes, into the wall gap | Bait for roaches; clean grease |
| Door thresholds, window frames | Yes | Weather-strip and caulk |
| Countertops, food cabinets | Never | Bait stations out of reach |
| Mattress, bedding | Only if labeled for bed bugs | Encasements; professional treatment |
| Open floors, carpet, upholstery | No | Wasted product and repelled insects |
| Within reach of bait | Never | Let the bait work |
| Closets and cabinets, with a fogger | Never | Fire and inhalation risk |
If you remember one rule, make it this: aim at the gap, not the surface. A finger-width band into the crack where the baseboard meets the floor, the hole where the pipe comes through, the hinge side of the cabinet. Nothing on a counter, a mattress or an open floor. Bait for ants and roaches before you spray anything, and keep the spray away from the bait once it is down. Then stop and watch for two weeks, because what hatches in that window is not a reason to spray again.
The short version
- Crack and crevice, never surfaces. Baseboards, pipe gaps, cabinet hinges, thresholds and window frames.
- Never food surfaces, never bedding unless labeled for bed bugs, never whole rooms. Broadcast spraying repels cockroaches into new rooms.
- Baits first for ants and roaches. The EPA's words. Sprays reach individuals; baits reach the colony.
- Never spray near bait. Clemson: it makes cockroaches avoid the bait.
- Cats and permethrin do not mix. Keep cats off treated areas until fully dry.
- Foggers: one per room, six feet from any flame, never in a closet. And they still miss the cracks.
Sources: US EPA, Do's and Don'ts of Pest Control, Safety Precautions for Total Release Foggers and Stay Legal and Safe in Treating for Bed Bugs; National Pesticide Information Center, Permethrin General Fact Sheet and Pyrethrins General Fact Sheet; UC IPM, Cockroaches; Clemson Cooperative Extension HGIC 2449, Cockroach Control; University of Kentucky Entomology, Cockroach Elimination in Homes and Apartments; Z. C. DeVries and colleagues, "Pervasive Resistance to Pyrethroids in German Cockroaches", Journal of Economic Entomology 112(5):2295-2301, 2019; E. Boné, P. A. González-Audino and V. Sfara, "Spatial Repellency Caused by Volatile Pyrethroids is Olfactory-Mediated in the German Cockroach", Neotropical Entomology 49(2):275-283, 2020; R. W. Baldwin and P. G. Koehler, "Toxicity of Commercially Available Household Cleaners on Cockroaches", Florida Entomologist 90(4):703-709, 2007.
Frequently Asked Questions
Into the gaps insects travel through and rest in, not onto open surfaces. That means the crack where baseboards meet the floor, the hole under the sink where pipes enter, the hinge side and back corners of lower cabinets, the wall gap behind the refrigerator and stove, door thresholds and window frames. A thin band directed into the gap outperforms a wet floor and keeps the product out of the space you live in.
Yes, if the product is labeled for indoor use and you follow that label exactly. The EPA's household rules are to read and follow the label, never use outdoor chemicals indoors, never assume twice as much is better, and keep children and pets away from treated areas until dry. Using a product any other way is a violation of federal law, and the label says so on every can.
Dogs tolerate most labeled indoor products once surfaces are dry. Cats are the exception: permethrin, the residual in many indoor sprays, is unusually toxic to them because their bodies break it down slowly, and they walk through treated areas and then groom. Keep cats out until everything is fully dry, treat only cracks rather than floors, and keep the product off anywhere a cat lies or eats.
Only with a product that is EPA-registered with bed bugs on the label, applied exactly where the label says, which for most consumer sprays is the cracks and joints of the bed frame rather than the sleeping surface. Ordinary indoor bug spray on a mattress is off-label and puts residue where you breathe all night. For bed bugs, encasements and a professional treatment do far more than any can.
It depends on the active ingredient. Contact sprays such as pyrethrins kill what they touch and break down within hours. Residual sprays are designed to persist: NPIC reports that 60% of permethrin applied indoors near a window was still on the surface after 20 days. Mopping, sunlight and porous surfaces all shorten that, which is another reason to treat the crack rather than the floor. Reapply on the label's schedule, not because you saw a bug.
Rarely. The EPA's precautions are one fogger per room, six feet from any ignition source, never in closets or cabinets, and two to four hours out of the house. Even used correctly, Kentucky's entomologists note very little of the insecticide penetrates the cracks and voids where pests actually live, and UC IPM warns foggers may repel and disperse cockroaches to other areas without killing them. The product lands on your counters instead.
Because the spray makes the insects avoid the bait, and the bait was the part that would have ended the problem. Clemson states that spraying a residual insecticide over bait placements makes cockroaches avoid it. Baits work by being carried back to the colony over days; in testing they cut German cockroach populations by 70 to 93% in a month. A can of spray within reach of them cancels that.
When you are seeing German cockroaches, which breed indoors and need baiting rather than spraying; when you suspect bed bugs at all; when the same insects return within a few weeks of a correct crack-and-crevice application, which means a harborage or entry point you cannot reach; or when anyone in the house has asthma, since repeated indoor spraying is a respiratory exposure. Our post on what a professional treatment actually covers explains the difference.
Photo credits: Clemson University, USDA Cooperative Extension Slide Series, CC BY 3.0 US, via Wikimedia Commons; Christian Fischer, CC BY-SA 3.0, via Wikimedia Commons; USDA APHIS PPQ, CC BY 3.0 us, via Wikimedia Commons.