*CORRECTION: This story originally incorrectly stated that Seresto collars "inject" pesticides into pets' skin. The story has been updated to say the collars slowly release pesticides into pets' fur. We regret the error.

Since March, Investigate Midwest, with its partner USA TODAY, has investigated the safety of Seresto pet collars. *The collars work by slowly releasing two pesticides into pets' fur to ward off fleas and ticks. The producer of the collars is Elanco Animal Health.

Here are the most important findings so far from our continuing investigation.

The EPA identified Seresto as being connected to a high number of incidents involving pets as early as 2015.

After getting a press inquiry from WNBC New York in July 2015, the U.S. Environmental Protection Agency launched an investigation into the collar. 

A December 16, 2015, powerpoint presentation by the EPA laid out a timeline for the investigation. 

In the presentation, the EPA had found that Seresto was “No. 1 by a wide margin” in terms of overall incident reports compared to other pet products that used pesticides, including spot-on treatments. The agency also conducted a comparative analysis of Seresto and other pet products, much of which was redacted in recently released documents.

The EPA has spent a lot of time looking at incidents, especially after Canada decided not to approve Seresto.

The EPA reviewed the incidents reports associated with Seresto, beginning in 2015. After Canada’s pesticide regulatory branch decided not to approve Seresto because of incident data in 2016, the EPA met with Bayer Animal Health (now Elanco) about incident data. The agency never took action.

The agency has internally compared Seresto to other flea-and-tick products for many years, but it’s unclear what those analyses found. 

Elanco says the product is safe.

In a public comment filed to the EPA in September, Elanco said its collar is safe despite reports of more than 86,000 adverse incidents, including 2,340 pet deaths since it hit the market nine years ago.

Those incidents, Elanco said in its 41-page comment, are likely related to other factors and not the collar itself. Because the collar is worn for months at a time and is always visible on the animal, it’s often cited in any health incident a pet has while wearing it, the Indiana-based company said. 

Elanco cited its own extensive studies and investigations into those reports that they say show the collar is safe. It also noted the incident rate has declined as sales increased — from 60 reports per 10,000 collars in 2013 to 17 per 10,000 in 2020.

The EPA is now considering taking action on Seresto. 

The EPA has a legal obligation to take action on a petition filed by the Center for Biological Diversity, and, this summer, the EPA launched a public comment period on the petition. The petition received more than 5,000 public comments, the majority of which were telling the EPA to take action on Seresto. 

It is unclear how quickly the EPA will choose whether or not to take action. In the past, petitions often took years to be resolved, but the EPA seems to be moving quickly with the petition on Seresto.

The collar has also been linked to harm to humans.

Between 2013 and 2018, 907 incidents were reported with humans, according to a September 2019 EPA assessment of risk to human health.

The assessment determined that there were 19 severe incidents. Of those, eight people had skin ailments, such as a rash or hives, and seven had neurological symptoms, which included numbness and headaches. 

Incidents listed by the EPA included:

  • A 12-year-old boy who slept in a bed with a dog wearing a collar started having seizures and vomiting. He had to be hospitalized. 
  • A 67-year-old woman who slept in a bed with a dog wearing a collar reported having heart arrhythmia and fatigue.
  • A 43-year-old man put collars on eight dogs and slept in the same bed as four of the dogs. A week later, he developed ear drainage and nasal and throat irritation and was told by a doctor that he had a hole in his ear drum. He removed the dog collars and the symptoms went away. He later reapplied the collars and the symptoms returned.

In a September response to the attempted ban of Seresto, Elanco told the EPA that reporting rates for humans were extremely low — less than one incident per 50,000 — and that few of these incidents were likely connected to the collar.

View stories in this investigation:

Seresto flea collar adverse incidents climb after company submits 11,000 more reports to EPA

The EPA internally raised concerns about Seresto flea collar for years, new records reveal

Seresto pet collars under EPA review, but the fight over their safety could take years

Popular flea collar linked to almost 1,700 pet deaths. The EPA has issued no warning.