Professional exterminator sprays typically contain synthetic chemicals called pyrethroids, which kill insects by disrupting their nervous systems on contact and continue working for 30 to 90 days after application. The specific product an exterminator uses depends on the pest, the severity of the infestation, and where the treatment is applied, but most indoor treatments rely on a small group of well-established chemical classes that work in predictable ways.
What Exterminators Actually Spray
The most common compounds in professional pest control sprays are pyrethrins and pyrethroids. Pyrethrins are natural insecticides derived from chrysanthemum flowers. Pyrethroids are their synthetic cousins, engineered to last longer and work more consistently indoors. Both are the backbone of residential pest control for cockroaches, ants, spiders, bed bugs, and most other household insects.
Beyond pyrethroids, exterminators may use products from several other chemical classes depending on the situation. Neonicotinoids target a different part of the insect nervous system and are common in bed bug treatments. Desiccants (like diatomaceous earth or silica gel) physically dry out insects rather than poisoning them. Insect growth regulators prevent immature insects from developing into adults, which is especially useful for long-term control of roaches and fleas. For bed bugs specifically, the EPA lists seven registered chemical classes across roughly 300 products, giving professionals a range of tools to rotate through when resistance becomes a problem.
Most professional sprays are applied as liquid residuals along baseboards, behind appliances, inside wall voids, and around the exterior perimeter of your home. Some treatments use gel baits or dust formulations in combination with sprays, but the liquid spray is what most people picture when they think of an exterminator visit.
How the Spray Kills Insects
Pyrethrin and pyrethroid sprays are contact toxicants. They work when an insect crawls across a treated surface and the chemical penetrates its body. Once absorbed, these compounds jam the on/off switches (sodium channels) in the insect’s nerve cells, keeping them locked in the “on” position. The result is uncontrolled nerve firing, convulsions, tremors, and rapid death. This is why you’ll often see insects behaving erratically or appearing more frequently in the days after treatment: they’re coming into contact with treated surfaces and losing the ability to function normally.
Insect growth regulators work on a completely different timeline. They don’t kill adult insects directly. Instead, they mimic natural hormones that control development, flooding immature insects with signals that prevent them from molting properly or reaching reproductive maturity. One category blocks the production of chitin, the material that forms an insect’s exoskeleton. Without it, the insect can’t build a new shell when it tries to grow, which is fatal. These products are slow-acting but effective at collapsing a population over weeks by ensuring young insects never become breeding adults.
How Long the Treatment Lasts
A professional perimeter spray generally provides protection for 30 to 90 days, depending on the product used, environmental conditions, and how much the treated surfaces are disturbed. Indoor applications along baseboards and in sheltered areas tend to last longer because they’re protected from rain, sunlight, and foot traffic. Outdoor treatments break down faster and may need reapplication on the shorter end of that range.
This is why most pest control companies recommend quarterly treatments for ongoing prevention. A single application handles the immediate problem, but insects from neighboring properties, eggs that survived the first treatment, or seasonal population surges can bring them back once the residual wears off.
Safety for Pets and Children
The National Pesticide Information Center recommends keeping pets out of treated areas until the spray has dried completely or for the time specified on the product label, whichever is longer. During the actual application, all pets should be removed from the home entirely or kept in untreated rooms. This is especially important with foggers (bug bombs), which disperse chemicals into the air throughout the space.
For children, the same drying rule applies. Most professionals advise staying out of the home for at least two to four hours after treatment. Good ventilation during the drying process, such as opening windows and running fans, helps reduce airborne residue. Once the spray has dried onto surfaces, the risk drops significantly because the active ingredients are bound to the surface rather than floating in the air. The dried residual is what continues killing insects for weeks afterward, and at the concentrations used indoors, it poses minimal risk to humans and pets walking across it.
Fish and reptiles are more sensitive than dogs or cats to many insecticides. If you have aquariums or terrariums, cover them and turn off their air pumps during treatment so they don’t pull contaminated air into the water.
What to Do After Spraying
The biggest mistake people make after a professional treatment is deep-cleaning the areas that were sprayed. Mopping along baseboards, scrubbing behind appliances, or wiping down treated surfaces with wet cloths removes the residual layer that’s doing the work. That residual is the whole point of a professional spray: it keeps killing insects for weeks after the technician leaves.
Normal cleaning in untreated areas is fine. You can sweep, vacuum, and dry-wipe in treated zones without much impact. The key is to avoid wet mopping or scrubbing directly along baseboards, cabinet edges, and other areas where the spray was applied. Countertops and food-preparation surfaces should be wiped clean before use, but these areas typically aren’t targeted during treatment anyway.
Keeping your kitchen clean actually helps the treatment work better, particularly for cockroach infestations. When food and water sources are eliminated, roaches are forced to seek out the gel baits and walk across treated surfaces instead of finding easy meals elsewhere. A spotless sink, dry counters, and sealed food containers make the exterminator’s products the only option available.
Why You Might See More Bugs at First
It’s common to see an increase in insect activity for the first week or two after treatment. This doesn’t mean the spray failed. Insects that were hiding deep in walls, under appliances, or inside cracks are now being flushed out by the chemicals and are stumbling across treated surfaces on their way out. You’ll often find them moving slowly, twitching, or already dead in open areas where you wouldn’t normally see them.
For cockroaches, this “flush out” period can last one to two weeks. For ants, it may take a few days for the colony to collapse as foragers carry residual chemicals back to the nest. Bed bug treatments often require multiple visits spaced two weeks apart because eggs are resistant to most sprays and need to be targeted after they hatch. If you’re still seeing healthy, active insects three to four weeks after treatment, that’s when a follow-up visit is warranted.