Yes, but only with a product whose label names indoor sites. Pyrethrin indoor use is settled by that label and nothing else, and never by the active ingredient alone. Plenty of pyrethrin concentrates are sold for barns, field crops and yards, and spraying one of those in a bedroom counts as illegal misuse. An indoor pyrethrin spray meant for kitchens and living rooms is a different formula at a different strength, and the back panel says so in plain print.
A line of small black ants came under my kitchen doorway every morning for a week. I noticed they walked the same path along the baseboard to a crumb spot by the trash can, then turned around and walked back out. UC IPM lists Terro Spider and Ant Killer among the home and garden products that carry pyrethrins, so that shelf is where I started. I checked the back panel for the site list before anything went on the floor. Then I sprayed the gap under the door and left the rest of the room alone.
Sunlight is what takes pyrethrins apart fast. NPIC puts the half-life at 11.8 hours in water with sunlight present and 12.9 hours on sunlit soil surfaces. Take the sun away and that number stretches out hard, because in water with no light the half-life runs 14 to 17 days. Your hallway baseboard gets no direct sun, so a treated strip of trim indoors is not on the same clock as a treated lawn. No source publishes an indoor half-life, so treat the residue as longer lived and plan around it.
The product list is long. NPIC counts pyrethrins in over 2,000 registered pesticide products, with foggers, sprays, dusts and pet shampoos among them. EPA counts over 3,500 products for pyrethrins and pyrethroids as a group. Those go in and around homes, on pets, in treated clothing and on farms. A pyrethrin fogger deserves the most thought of the bunch, since it fills a whole room instead of one crack. UC IPM lists PT Clear Zone III Metered Pyrethrin Spray and Pyronyl Fogging PF as professional products, and those are meant for a room that has been prepped first.
Most of what you buy is not pure pyrethrin either. Most of these products are mixed with synergists such as piperonyl butoxide and MGK-264. So the fine print on the can covers more than one chemical, and the directions were written for that whole mix. Read the site list first, because that is where pyrethrin indoor use gets decided. If the label names your kitchen or your basement, you are clear to use it there, and if it names only turf and livestock housing, put it back.
Cover the fish tank before you spray anything and switch off the air pump that pulls room air into the water. NPIC rates pyrethrins highly to very highly toxic to fish, and very highly toxic to lobster, shrimp, oysters and aquatic insects. That one detail catches people out more than any other, because the tank sits in the same living room as the ants. Open the windows and give the room real air movement while you work.
Wear chemical resistant gloves, long sleeves and goggles even for a small job in the kitchen. UC IPM gives that advice for a blunt reason. Many consumer labels leave protective equipment off the page, and a shopper reads that silence as permission. Silence is not permission. Match the room you are standing in to the household insecticide label in your hand. Follow its directions on where to spray and how long to stay out, and buy a different product when the two do not line up.
Read the full article: Pyrethrin: What It Kills and How Safe It Is
