SAN FRANCISCO (CBS SF) — Experts say fleas may be mutating and becoming more resistant to topical anti-flea treatments, making them peskier than ever for Bay Area pet owners trying to get rid of them.

One vet KPIX spoke to said the smelly solutions designed to kill fleas that pet owners have been applying to their cats and dogs may not help thanks to survival of the fittest flea.

Katherine Van Ekert with VetPronto is one of many Bay Area vets that are telling pet owners the anti-flea solution produced by companies like Frontline and Advantage that they are buying isn’t working.

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“You can imagine when we’re applying a flea product that’s designed to kill a flea and those fleas have random mutations the genes that are resulting and are allowing the fleas to survive are going to win,” explained Van Ekert.

Fleas may have mutated, but Van Ekert says the flea problem also has to do with the warmer weather.

“This past summer has been dragging on months and months, so flea populations, they have been really small to start off with and they’re growing,” said Van Ekert. “Normally, they go into dormancy in the winter, so they will hibernate for a while. But it just hasn’t been cold enough for that yet.”

Pet owner Kelly Edwards said his dog Fred has had flea issues for the past year.

“I’m definitely hearing this for the first time, and that actually is relieving to me,” said Edwards.

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But Janine Aiello, another pet owner, told KPIX she knew this all along.

“He’s never gotten rid of any fleas with that topical solution,” said Aiello. “I’ve tried every single brand topically and none have ever worked.”

Her message to pet owners? Stop buying the stuff.

“I think they’re wasting their money because they don’t work as far as relieving the dog of fleas,” said Aiello.

Instead, vets are recommending oral flea medications like Nextguard, which Frontline also makes.

Despite what vets have recommended, Frontline and Advantage topical solutions are still available in stores. KPIX reached out to the companies, but have not received any response.