Is Seresto’s Flea and Tick Collar Dangerous for Dogs?

As a responsible dog parent, you give your pup the preventive treatments they need like heartworm and flea and tick meds. But if you've relied on Seresto’s flea and tick collar, you may want to switch brands: A recent report found that over the course of almost a decade, Seresto's flea and tick collar reportedly harmed 75,000 dogs, cats, and humans. Among the incidents, 1,698 were pet deaths and 1,000 indicated harm to people. 

The reports were made to the Environmental Protection Agency (EPA), but unfortunately, the organization has not made the public aware of the collar’s risks — which is why the Midwest Center for Investigative Reporting co-published an investigative piece on the issue with USA Today. The piece draws from documents obtained from the Center for Biological Diversity, an EPA watchdog.

In 2019, the EPA issued an internal memo that looked at flumethrin — one of Seresto collars’ active ingredients — and reviewed the human incidents that had been reported. In people, clinical signs varied widely: skin rashes or lesions; numbness, tingling, or pain; and nasal, ocular, or throat irritation were among them. These signs appeared after placing the collar on the pet and nuzzling them, or after sleeping with the pet. More serious events were also reported. In many cases, clinical signs improved after the collar was removed. However, animal deaths appear to have been very sudden. 

In addition to flumethrin (4.5%), Seresto collars also contain imidacloprid (10%) as an active chemical ingredient. Imidacloprid belongs to the neonicotinoid class of insecticides most commonly used on crops in the United States. Despite neonicotinoids being connected to massive endangerment of bees and butterflies, the EPA proposed reapproving imidacloprid and other class members last year.

Seresto, advertised to provide eight-month protection against fleas and ticks, is the only flea-repellent on the market that contains flumethrin, per the Midwest Center, and it’s speculated that these harmful side effects could be the result of the combination of the two pesticides (though this has yet to be confirmed).

As with most pesticides, data supporting the registration of Seresto was conducted only by the company that produced it — in this case, that’s Bayer AG, a massive German agribusiness and pharmaceutical company. The majority of the studies looked at each pesticide individually. But, as the Midwest Center report details, a 2012 Bayer study found that together, flumethrin and imidacloprid have a “synergistic effect,” meaning they are more toxic together. The study also found that the “unique pharmacological synergism” works as quickly as six hours to prevent ticks from attaching and feeding, preventing disease transmission.

Karen McCormack, a retired EPA employee who worked as both a scientist and communications officer, told the Midwest Center that the collars have the most incidents of any pesticide pet product she’s ever seen. “The EPA appears to be turning a blind eye to this problem, and after seven years of an increasing number of incidents, they are telling the public that they are continuing to monitor the situation,” she said. “But I think this is a significant problem that needs to be addressed sooner rather than later.”

In 2019, Bayer sold its animal-health division to Elanco Animal Health for a combination of $7.6 billion and Elanco stock, which means that Seresto is now an Elanco product with Bayer still retaining shares in it. According to the Midwest Center, Elanco spokesperson Keri McGrath said in an email that the company “takes the safety of our products very seriously and thoroughly investigates potential concerns related to their use.” 

McGrath pointed out that regulatory authorities have approved the product in more than 80 countries, and that the EPA is in the final stages of re-approving both pesticides. (There is no timeline on the final decision.)

It’s likely that even these high numbers of reports are only the tip of the iceberg. Few people would think of reporting an incident involving a flea collar to the EPA, which leaves a lot of room for holes in the data. 

For clarification on this, we reached out to the U.S. Food and Drug Administration’s (FDA) Center for Veterinary Medicine (CVM). According to CVM’s Siobhan DeLancey, the EPA has jurisdiction over the Seresto cases because the collar is classified as a pesticide. The FDA, however, has oversight of flea-and-tick products that are classified as drugs, she adds, and their regulation is separate from that of the EPA. 

“We strongly encourage people whose dogs have had side effects to report their experiences to the company and/or to us,” DeLancey urges. “Manufacturers are required to provide the reports they receive to us, but people can also report directly to FDA if they prefer. Here’s how.”

The bottom line: If you use the Seresto collar on your dog and either of you have experienced any harmful effects, contact the EPA and the FDA today, and remove the collar and dispose of it responsibly. In most cases — despite what the company says on its product information sheet — that means not putting it in the trash. Instead, take it to your area’s household hazardous waste facility.