If you’ve kept up with your dog’s flea and tick prevention, you’ve done the responsible thing. So it’s jarring to learn that one of the most popular products for the job, the Seresto collar, has been at the center of a years-long safety fight. Before you panic or toss the collar in a drawer, it’s worth separating the number that made the headlines from the number regulators could actually stand behind. Both are real. The distance between them is the story.
Where the alarm started
The controversy broke open when the Midwest Center for Investigative Reporting, working with USA Today, published an investigation drawing on records obtained through a watchdog group. The reporting found that across roughly a decade, the Seresto collar had been linked to about 75,000 incidents involving dogs, cats, and people. Within that total were 1,698 reported pet deaths and around 1,000 reports of harm to humans.
Those reports went to the Environmental Protection Agency, which regulates the collar because it’s classified as a pesticide rather than a drug. (Flea and tick products classified as drugs fall to the FDA instead, a jurisdictional split that has muddied the public picture more than once.) A retired EPA scientist told investigators the collar had generated more incident reports than any pet pesticide she had come across in her career, and criticized the agency for monitoring the problem rather than acting on it.
What’s actually in the collar
Seresto works using two active ingredients: flumethrin at 4.5 percent and imidacloprid at 10 percent. Imidacloprid is a neonicotinoid, the insecticide class widely used on crops and tied to serious harm to bees and other pollinators. Flumethrin is more unusual; Seresto is the only flea collar on the market that uses it.
The concern isn’t necessarily either chemical alone. A 2012 study by Bayer, which developed the collar, described a “synergistic effect” between the two, meaning they’re more potent together than apart. That combination is also what makes the product work as advertised, disrupting ticks within hours before they can attach and transmit disease. But as with most pesticides, the safety data supporting approval came largely from the manufacturer, and mostly examined each ingredient on its own rather than the pair.
An EPA memo from 2019 catalogued the human reports tied to flumethrin: skin rashes and lesions, numbness, tingling, pain, and irritation of the nose, eyes, or throat, often after handling or sleeping near a collared pet. In many of those cases, symptoms eased once the collar came off. Animal deaths, by contrast, tended to be sudden.
Seresto’s corporate history adds a wrinkle. Back in 2019, Bayer offloaded its entire animal-health arm to Elanco in a multibillion-dollar deal, which is why the collar is an Elanco product today. Elanco has said it takes product safety seriously, investigates concerns, and notes that regulators in more than 80 countries have approved the collar.
What newer findings changed
Here’s the part the original alarm couldn’t include, because it hadn’t happened yet.
In July 2023, after its review, the EPA decided the collar could stay on the market, but with new strings attached. The agency limited the approval to five years, required Elanco to ramp up adverse-event reporting and veterinary outreach, and ordered new warning labels flagging common side effects and telling owners to remove the collar if problems appear. It also split Seresto into separate registrations for cats and dogs so incident data can be compared more cleanly.
The EPA’s own analysis reframed the death figure in an important way. When the agency examined reported deaths, the ones it could tie “probably” or “definitely” to the product were mostly cases of mechanical injury, strangulation or trauma from the collar itself, often linked to a failure of its breakaway release mechanism, rather than poisoning from the chemicals. Elanco was directed to reassess that release mechanism. Among the tens of thousands of dog cases the EPA reviewed, the most common complaint by far was itchy skin (about 54 percent), followed by lethargy and loss of appetite at roughly 10 percent each.
That doesn’t close the case. A 2024 EPA Inspector General report concluded the agency still hadn’t fully evaluated the collar’s safety, and by then the running tally of incident reports had climbed past 100,000, with several thousand reported pet deaths, still more than any other product the EPA oversees.
“Incident reports are a signal, not a verdict, and the honest read is that we don’t yet have a clean answer,” says Dr. Lena Park. “What I tell clients is that itchy, irritated skin under a collar is common and worth acting on, and that the strangulation risk is a real, physical thing to check for. If your dog reacts, take the collar off and call your vet rather than waiting it out.”
What to do with your own dog
The practical takeaway hasn’t changed much even as the numbers have been re-sorted. If your dog wears a Seresto collar and either of you develops symptoms, skin trouble, lethargy, behavioral or neurological changes in your dog, or rashes and irritation in yourself, remove it and talk to your vet. Report the incident to both the EPA and the FDA; most owners never think to, which is exactly why the data has holes.
And dispose of the collar properly. Despite what the packaging may suggest, a pesticide collar generally shouldn’t go in your household trash. Take it to your area’s hazardous waste facility instead.
Flea and tick prevention still matters, and plenty of effective alternatives exist, including vet-prescribed oral and topical products. The goal isn’t fear. It’s making the call with the real numbers in front of you.
References
- U.S. EPA. “Seresto Pet Collar Review.” epa.gov
- U.S. EPA. “EPA Requires Additional Mitigation Measures for Seresto Pet Collars,” 2023. epa.gov
- American Veterinary Medical Association. “EPA confirms registration, safety of Seresto collar,” 2023. avma.org
- Investigate Midwest. “EPA rules popular flea and tick collar Seresto stays on the market, but with added mitigations,” 2023. investigatemidwest.org
- U.S. EPA Office of Inspector General. Report on pet collar incident evaluation, 2024.
