Flumethrin (Seresto flea and tick collars)

Pet incident reports and EPA's 2023 decision

EPA registered flumethrin and the Seresto collar in March 2012. From 2012 through 2022 the agency received more than 100,000 incident reports involving the collars, and by November 2022 more than 2,500 reports of pet deaths and nearly 900 reports of human incidents.^[4]

In July 2023 EPA said it had finished reviewing the reports. Many of the 1,400 deaths reported from 2016 through 2020 lacked the details needed to determine a cause, and in some moderate or severe cases, symptoms eased when the collar came off or returned when it was put back on.^[4]

The July 13, 2023 approval added the adverse-event warnings now printed on the labels, with instructions to remove the collar and report the incident. It made the registration expire after five years unless extended, and it requires Elanco to file annual incident and sales reports with more detail about each case.^[1][4]

In February 2024 EPA's Office of Inspector General found that the agency's handling of the reports had not given assurance that the collars can be used without unreasonable adverse effects on pets. It noted that EPA had not done the domestic animal risk assessments it planned in the registration reviews of flumethrin and imidacloprid and still relied on a 1998 companion animal safety study guideline the report called inadequate.^[4]

Dog collars and the cat collar

The dog collars (EPA Reg. No. 11556-155) are sold as Seresto Small Dog, for dogs up to 18 lb, and Seresto Large Dog, for dogs over 18 lb, from 7 weeks of age. They are labeled for fleas, ticks and lice, and the label's tick claims name blacklegged (deer) ticks, American dog ticks, brown dog ticks and Lone Star ticks.^[1]

Seresto Cat (EPA Reg. No. 11556-191) is a separate registration for cats and kittens 10 weeks of age and older, labeled for fleas and ticks. The reactions reported most often in cats are at the collar site: hair change, sores, itching, redness, inflammation, bleeding, burns and ulcers. Behavior changes, lethargy, loss of appetite and vomiting come next on the label's list.^[2]

Where it is used

Each dog wears one collar fastened around the neck, snug enough that two fingers fit comfortably underneath. The excess is cut off no more than 1 inch past the loops, except on a growing puppy.^[1]

Fleas already on the dog die within 24 hours of fitting the collar, and after that new fleas are killed within 2 hours. Pupae already in the home can keep emerging for 6 weeks or longer, so the label says to treat the pet's living areas with a product approved for home use.^[1]

Ticks attached before treatment may not die right away, so remove them when you fit the collar. Protection against new ticks starts 48 hours after it goes on, and new ticks are repelled or killed as quickly as 6 hours after that.^[1]

The collar is water resistant, but to get the full 8 months a dog shouldn't be bathed more than once a month. For dogs that swim once a month or more, the label cuts protection to 5 months for fleas and 7 months for ticks.^[1]

Products and registrations

Label rates

How to apply it, step by step

Steps for Seresto Large Dog or Seresto Small Dog collar (4.5% flumethrin, 10% imidacloprid), EPA Reg. No. 11556-155, taken from its label^[1]. Other products with this active ingredient have their own labels; follow yours.

1. Protective gear

• Keep the collar sealed in its bag and outer package until you're ready to use it. Don't let children play with the collar or its reflector clips or put them in their mouths; the small parts are a choking hazard.^[1]
• Avoid getting it in your eyes or on your skin or clothing, and wash thoroughly with soap and cold water after fitting it. People who react to the collar's ingredients should avoid touching it.^[1]

2. Before you spray

• The collar is for external use on dogs and puppies 7 weeks of age and older only, and the label says not to use it on other animals. The Small Dog collar is for dogs up to 18 lb and the Large Dog collar for dogs over 18 lb.^[1]
• Ask your veterinarian first if the dog is debilitated, aged, breeding, pregnant or nursing, or is on any medication.^[1]
• Remove ticks already on the dog when you put the collar on, because ticks attached before treatment may not die right away.^[1]

3. Mixing

• There's nothing to mix or measure: each dog wears one collar. Take it out of the protective bag right before use, unroll it, and make sure no bits of the plastic connectors are left inside.^[1]

4. Applying

• Push the end through the buckle and adjust it so two fingers fit comfortably between the collar and the neck, neither too tight nor loose. Pull the excess through the loops and cut it off no more than 1 inch beyond them, unless the dog is a growing puppy that needs extra length.^[1]
• If you add the three reflector clips, space them evenly on the part of the collar that doesn't overlap and press until they click. Once fastened they close for good and can't be reopened.^[1]

5. After you spray

• Leave the collar on continuously for the 8-month protection period and replace it after 8 months. Check the fit now and then, especially on fast-growing puppies. Don't attach a leash to it, which can break it; a lost collar can be replaced right away.^[1]
• Dogs not used to collars may scratch for the first few days. Slight hair loss or a mild skin reaction under the collar usually clears within 1 or 2 weeks without taking it off. If you see itchy skin, eczema, lethargy, behavior changes, loss of appetite, muscle tremors, convulsions or loss of balance, remove the collar and call your veterinarian.^[1]

First aid

• The collar label has no separate first aid section. It gives an Elanco phone number for medical emergencies involving people or animals (1-800-422-9874, or 1-800-255-6826 on some packages) and says to have the label with you when you call a poison control center or doctor or go for treatment.^[1]
• Report a suspected reaction in your pet to Elanco or through EPA's web page for reporting pesticide incidents involving pets.^[1]

Storage, spills and disposal

• Store collars in the original unopened package in a cool, dry place children can't get to, and don't contaminate water, food or feed by storage or disposal.^[1]
• Put the pouch and an expired collar in the trash. The outer box can go in the recycling or the trash.^[1]

Need the amount for your sprayer? Use the mixing calculator, which works from the same label rates.

Safety and environmental hazards

People

The collar labels print no signal word. They say to keep children from playing with the collar or putting it in their mouths, to avoid contact with eyes, skin and clothing, and to wash with soap and cold water after fitting it; people sensitive to the ingredients should avoid touching it. The concentrated technical flumethrin sold for formulating products is another matter: its label carries the signal word WARNING and says it may be fatal if swallowed or absorbed through the skin. By November 2022 EPA had received nearly 900 human incident reports involving Seresto collars.^[1][3][4]

Pets

The dog label lists the adverse events reported to EPA, most frequent first: itchy skin, eczema, lethargy, behavior changes, reactions where the collar sits, loss of appetite, hyperactivity, muscle tremor, vocalization, convulsions and loss of coordination. If these appear, remove the collar and consult a veterinarian. EPA's Inspector General reported that by November 2022 the agency had received more than 2,500 reports of pet deaths involving the collars; EPA said many of the death reports it reviewed lacked the details needed to determine a cause.^[1][4]

Bees and pollinators

Neither the collar labels nor the flumethrin technical label carries a bee hazard statement. The collar releases its active ingredients onto the animal's skin.^[1][3]

Fish and water

The flumethrin technical label states that it is toxic to fish and aquatic invertebrates and must be kept out of lakes, streams and ponds. The collar labels say not to contaminate water, food or feed by storage or disposal.^[3][1]

Common questions

Can I put a Seresto dog collar on my cat?

No. The dog collar's label says it is for external use on dogs only and not to use it on other animals. Cats need the separate Seresto Cat collar, which is registered for cats and kittens 10 weeks of age and older.^[1][2]

How long does a Seresto collar last if my dog swims?

The label gives 8 months under normal conditions, as long as the dog isn't bathed more than once a month. For a dog that swims once a month or more, protection drops to 5 months for fleas and 7 months for ticks.^[1]

What should I do if my pet reacts to the collar?

Take the collar off and call your veterinarian. Both labels list the reactions reported to EPA and ask owners to report suspected adverse events to Elanco or through EPA's web page for pet pesticide incidents.^[1][2]

Is Seresto still approved after the reports of pet deaths?

EPA's July 2023 review concluded that the collars continue to meet its standards under federal pesticide law, but it limited the approval to five years and required new label warnings and more detailed incident reporting. In 2024 EPA's Inspector General said the agency still needs to determine whether the collars pose an unreasonable risk to pets.^[4][1]

Sources

1. U.S. EPA Pesticide Product Label System, “Seresto Large Dog and Seresto Small Dog (PNR1427 Insecticide) label, EPA Reg. No. 11556-155 (EPA-stamped, July 13, 2023).” www3.epa.gov/pesticides/chem_search/ppls/011556-00155-20230713.pdf (accessed 2026-11-08)
2. U.S. EPA Pesticide Product Label System, “Seresto Cat label, EPA Reg. No. 11556-191 (EPA-stamped, July 13, 2023).” www3.epa.gov/pesticides/chem_search/ppls/011556-00191-20230713.pdf (accessed 2026-11-08)
3. U.S. EPA Pesticide Product Label System, “Flumethrin Technical label, EPA Reg. No. 11556-154 (EPA-stamped, Mar. 14, 2013).” www3.epa.gov/pesticides/chem_search/ppls/011556-00154-20130314.pdf (accessed 2026-11-08)
4. U.S. EPA Office of Inspector General, “The EPA Needs to Determine Whether Seresto Pet Collars Pose an Unreasonable Risk to Pet Health, Report No. 24-E-0023 (February 29, 2024).” www.oversight.gov/sites/default/files/oig-reports/EPA/24-E-0023.pdf (accessed 2026-11-08)
5. Insecticide Resistance Action Committee, “IRAC Mode of Action Classification Scheme, Version 11.5 (Feb. 2026).” irac-online.org/documents/moa-classification/ (accessed 2026-11-08)