The label is the law. Rates and restrictions below are taken from the product labels listed under Sources. Your product's own label governs; read it before you mix or apply. Mixing calculator · Disclaimer
- Active ingredient
- Cyphenothrin (CAS 39515-40-7)
- Chemical class
- Pyrethroid; IRAC lists cyphenothrin, as its (1R)-trans isomers, in Group 3A, the sodium channel modulators that act on insect nerves.[2]
- Mode of action
- IRAC Group 3A: Sodium channel modulators: pyrethroids and pyrethrins[2]
- Signal word
- PetArmor FastAct for Dogs (20%) (registered as Cyphenothrin Squeeze-On for Dogs (20%)): Caution[1]
Side effects to watch for
Some dogs show redness, scratching or other irritation where it was applied, and vomiting or diarrhea have been reported.[1]
If you see signs of sensitivity, bathe the dog with mild soap and rinse with lots of water, then call your vet or the number on the package.[1]
Part of a wider flea plan
The label says to use it alongside steps that cut fleas in the dog's surroundings, such as bedding, carpets, the kennel and the yard. It does not replace heartworm medicine.[1]
Where it is used
Weigh your dog first and buy the tube made for that weight band. Use the whole tube on one dog, and never split one between dogs.[1]
Cut the tip with scissors, part the hair with the open end, and squeeze the full dose onto the skin. The label says to apply it indoors.[1]
Reapply monthly at most, never sooner than every 30 days. Don't bathe the dog or let it swim for 24 hours afterward.[1]
Don't treat a dog with more than one pesticide product at a time; the label warns overdosing can cause serious illness or death.[1]
Products and registrations
| Product | Registrant | EPA Reg. No. | Active % | Formulation | Signal word |
|---|---|---|---|---|---|
| PetArmor FastAct for Dogs (20%) (registered as Cyphenothrin Squeeze-On for Dogs (20%))[1] | Sergeant's Pet Care Products, LLC | 2517-131 | 20.0% | spot-on liquid in single-dose tubes | Caution |
Label rates
| Product | Use | Pests | Rate |
|---|---|---|---|
| PetArmor FastAct for Dogs (20%) (registered as Cyphenothrin Squeeze-On for Dogs (20%)) | Dogs and puppies 9 to 20 lb, at least 12 weeks old | Fleas; American dog, blacklegged (deer) and brown dog ticks; repels mosquitoes | 1.5 mL product per dog[1] One whole 0.05 fl oz tube, squeezed onto the skin between the shoulder blades or as a line down the back. |
| PetArmor FastAct for Dogs (20%) (registered as Cyphenothrin Squeeze-On for Dogs (20%)) | Dogs 21 to 39 lb, at least 12 weeks old | Fleas; American dog, blacklegged (deer) and brown dog ticks; repels mosquitoes | 3.0 mL product per dog[1] One whole 0.10 fl oz tube. |
| PetArmor FastAct for Dogs (20%) (registered as Cyphenothrin Squeeze-On for Dogs (20%)) | Dogs 40 to 60 lb, at least 12 weeks old | Fleas; American dog, blacklegged (deer) and brown dog ticks; repels mosquitoes | 4.5 mL product per dog[1] One whole 0.15 fl oz tube, applied as a line from the back of the neck to midway down the back. |
Safety and environmental hazards
People
Signal word CAUTION: causes moderate eye irritation and is harmful if swallowed or absorbed through skin. Wash with soap and water after handling, and don't let children apply it.[1]
Pets
Never use it on cats; the label says it may be fatal. Keep cats and other dogs away from the treated dog for 24 hours, and ask a vet first for aged, pregnant, nursing, medicated or ill dogs.[1]
Bees and pollinators
The label has no bee statement. It is applied to a dog's skin indoors, not sprayed outdoors.[1]
Fish and water
Never pour a partly used tube down any drain or sewer; call your local solid waste agency about disposal options.[1]
Common questions
- Is PetArmor FastAct safe for cats?
- No. The label says do not use on cats, may be fatal, and to call a vet right away if it gets on or into a cat.[1]
- How fast does cyphenothrin kill fleas and ticks?
- The label claims it starts killing fleas within 1 hour and kills listed ticks within 3 hours, lasting about a month.[1]
- Which ticks does it kill?
- The label lists the American dog tick, blacklegged tick (deer tick) and brown dog tick.[1]
Sources
- U.S. EPA Pesticide Product Label System, “Cyphenothrin Squeeze-On for Dogs (20%) label, EPA Reg. No. 2517-131 (EPA-stamped, Nov. 1, 2024).” www3.epa.gov/pesticides/chem_search/ppls/002517-00131-20241101.pdf (accessed 2026-10-06)
- Insecticide Resistance Action Committee, “IRAC Mode of Action Classification Scheme, Version 11.5 (Feb. 2026).” irac-online.org/documents/moa-classification/ (accessed 2026-10-06)