California Weighs Limits on Key Ingredient in Spot-On Flea and Tick Control Products

Every year, thousands of California pet parents rely on flea and tick prevention products to protect their dogs and cats during the pests’ most aggressive season. But an ingredient that’s common in over-the-counter topical flea and tick treatments has raised concerns among California regulators.

Fipronil, an active ingredient in more than a dozen brands of spot-on flea and tick products, poses health risks to people and aquatic wildlife, the California Department of Pesticide Regulation reported in a July memorandum. To reduce risks, the DPR is weighing multiple options, including designating the pesticide a “restricted material,” a move that could effectively take some popular products off pet store shelves in the state.

Pet products accounted for nearly 57% of all fipronil sold in California (averaging 73,000 pounds per year) between 2020 and 2022, according to the DPR. Approximately 31 dog spot-on, 30 cat spot-on, and three dog/cat sprays are available in California, the department said.

Switching from fipronil-containing flea and tick products to pest-control alternatives that don’t contain the chemical (the DPR counted 89) would increase pet owners’ monthly pest-control costs by an average of $3.64 per cat and 56 cents per dog, the DPR said.

Impact of fipronil on California waterways

Fipronil ends up in waterways through multiple routes, the DPR said. When owners bathe their pets after applying a spot-on product, wash their pet’s bedding, or wash their own hands post-application, the chemical goes down the drain.

And wastewater treatment processes aren’t effective at removing fipronil from water.

Fipronil was present in 100% of 241 wastewater samples that entered 33 treatment plants the DPR tested between June 2019 and May 2024. And it was present in 95% of 241 treated samples tested during the same time period at the same treatment facilities.

Risks to pet owners and pet care professionals

The DPR’s memos also raised concerns about how prolonged exposure to fipronil might affect pet owners and professionals like groomers and veterinary workers.

In a 2023 study, the department found that long-term exposure to the chemical could pose health risks, and it pointed to home use of pet sprays and spot-on products as a significant source of exposure.

The DPR reviewed thousands of adverse reactions to pet products containing fipronil and found common complaints included eye and skin irritation; gastrointestinal problems, including vomiting and diarrhea; neurological issues, like vertigo, headaches, and disorientation; spinal pain; coughing and throat irritation; and tremors.

Fewer veterinary practices are using fipronil products than a decade ago, the California Veterinary Medical Association told the DPR in a letter earlier this year. “Newer and more effective systemic treatments” have taken the place of fipronil, the CVMA said.

But the association also acknowledged that spot-on products have been “game-changers” for pet owners, especially those who can’t afford veterinary-level flea and tick control.

What’s next? Regulators seek feedback on possible solutions

On Sept. 16, the DPR issued a follow-up memorandum proposing multiple ways to reduce fipronil risks, including possibly limiting the number of applications allowed per year, restricting post-application pet bathing, requiring groomers to wear protective gear when applying spot-on products, or designating the pesticide a restricted material.

The department noted that whatever course it ultimately chooses, educating consumers on how fipronil can affect people and aquatic animals will be “critical,” but not enough on its own.

The DPR is seeking feedback from the public and “any relevant information and commentary” on how to address fipronil risks. It’s accepting comments until Nov. 16.

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