We found them on the shelves of major pet supply stores and supermarkets. Everything from sprays and shampoos to spot-on drops. The treatments are designed to kill fleas and ticks and they're all approved by the U.S. Environmental Protection Agency (EPA).
But some pet owners, like Heidi Woehler, believe the shampoo she used killed her cat.
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We first told Woehler's story last month. We also revealed how the U.S. EPA has received thousands of reports of problems from flea and tick products. The EPA says in 2008 alone, it received more than 44,000 reports of potential incidents associated with spot-on products.
When we asked Marty Monell with the EPA why there's a sharp increase in the number of reported incidents from these products, she said, "That's one of the issues we're looking at."
The EPA says it's now "intensifying its evaluation" of flea and tick treatments, especially those "spot-on" products.
"We believe these products are safe if used as (directed). But we are also looking into other possible causes of these incidents," Monell tells NBC Los Angeles.
The Canadian government has gone a step further, warning pet owners that there "may be potential for adverse reactions" to dogs and cats from some of these products.
"We're seeing a range of adverse effects, ranging from very mild affects such as skin irritation, up to serious affects that do include death." said Cheryl Chafee with Health Canada.
Veterinarians across the country tell us they believe many over-the-counter flea and tick products can harm a small percentage of pets, because they contain pesticides.
"I think they need to be re-looked at and maybe relabeled," said Dr. Mark Grossman, a veterinarian and consultant to the Veterinarian Information Network.
"It needs to be taken off the market," Woehler tells NBC Los Angeles.
Bio Spot, the maker of the shampoo Woehler used, told her it didn't believe its flea and tick shampoo killed her cat.
Meanwhile, both the EPA and Canadian government tell us their investigation could result in further restrictions on these products, possibly even pulling some from the market.
"Our goal is to protect pets," Monell tells NBC Los Angeles.
It's important to note the EPA says just because an incident is reported, doesn't mean a product is to blame. We heard from some major manufacturers of flea and tick products.
Sergeant's says its products are safe and it "welcome the EPA's increased evaluation of the use of spot-on pesticides."
Bio Spot says it "takes all concerns and claims associated with our products very seriously," and, "We are confident ...That our topicals will be shown to exhibit a wide margin of safety."
The Hartz Mountain company says its products are safe and that it is significant that no Hartz dog product is mentioned in the EPA's advisory. They go on to say it is "also significant that Hartz's cat products account for only 2 percent of the potential incidents reported to the EPA -- far less than their market share."
If you have concerns, talk with your vet about choosing a flea and tick product and carefully read the directions before using any of these products.
Do you have a story for us to investigate? email us at Joel.Grover@nbcuni.com