Why does flea-treating a pet sometimes not seem to work? Is the product not doing what it should, or are fleas ‘immune’ to the product? Our pet experts know exactly what’s going on here and have the answers pet parents need. Spoiler alert: seeing fleas alive after treatment doesn’t mean it’s not working. Phew!
That depends on the product – take a look at the product packaging or leaflet for specific details. FRONTLINE PLUS ® and FRONTLINE ® SPOT ON kill fleas within 24 hours of them arriving on the pet, while FRONTLINE TRI-ACT ® kills fleas within 6 hours of them jumping on a dog. There are a couple of key things to remember, whichever treatment you’ve used.
The flea has to come into contact with the ingredient, absorb it and then start to feel the effects. It’s a little like catching a cold – time elapses between us having contact with a cold virus and then becoming ill.
No product stops fleas from jumping onto pets
This means that, regardless of which flea treatment is used, we may still see new fleas on our pets before the flea treatment kills them. So, even if the treatment kills all fleas on a pet within 24 hours, for example, the next day new hitchhiker fleas could jump onto the pet. These new arrivals will themselves take up to 24 hours to be killed. And so on, every time a pet goes into an area where fleas are present. The important thing is that these newly arriving fleas are being killed by the treatment.
Why am I still seeing fleas days after treatment?
There are two other reasons for this.
One is that some flea treatments make fleas more active before they die. For example, the ingredient in FRONTLINE ® products kills fleas by making them hyper excited. This makes them move around up to the top of the pet’s hair where they’re easier to spot. So, seeing fleas more after treatment is a sign the product is working, strange as that might sound.
The other reason is, as mentioned above, fleas will still jump on our pets from an infested environment. So, if our pets go somewhere that’s scattered with flea life stages – such as gardens, parks or even our homes if there’s an infestation going on – new fleas will keep jumping on the pet. But don’t worry, these new arrivals will keep being killed as long as the pet is treated.
The fleas on a pet are just 5% of the problem.
95% are in the environment as flea eggs, larvae and pupae.
How long does it take to solve a flea infestation?
One last thing to remember
Seeing fleas after treatment isn’t really about how long it takes for flea treatment to work or for fleas to die. It’s about the number of life stages in the pet’s environment that develop into new fleas and jump on a pet. That’s why regular flea prevention for dogs and cats at the correct treatment interval is important.
This helps our pets stay healthy and it helps stop flea infestations from developing – a win-win for us pet parents and our furry family members.
MORE FROM FLEAS
Spotted fleas in your home but don't have a cat or dog? FRONTLINE's pet experts outline why and how to get rid of these critters for good.
Spotted fleas in your home? The pet experts at FRONTLINE ® can help you spot the signs of an infestation and what you can do about it.
Wherever your pet goes, they are at risk of picking up hitchhiker fleas from eggs dropped by untreated pets and wildlife.
Fleas are out in full force during the summer, hiding in homes, parks and gardens. Learn all the essentials as we teach you how to spot fleas on your dog or cat.
Don't panic! Here are 5 key things you need to do now to get rid of fleas! Follow our action plan to beat a flea infestation from vacuuming to washing pet bedding.
Prevention is better than cure - learn how to prevents and protect your pets from fleas all year round, with expert advice.
Get answers from the experts
Got a question about fleas, ticks or worms? We can help! Take a look at our FAQs or send us a message.
Two Paragraph Two Paragraphs 
Join the #PetParentClub
We’ve got an amazing community of dedicated pet parents on our social channels. You’ll find pet care tips and cute pics, plus advice from our pet experts. We can’t wait to welcome you to the club!
Call to Action
FRONTLINE HomeGard ® is a biocide. Use biocides safely. Always read the label and product information before use. Further information available from Boehringer Ingelheim Animal Health UK Ltd, RG12 8YS, UK. Email: petsuk@boehringer-ingelheim.com. FRONTLINE HomeGard ® is a registered trademark of Boehringer Ingelheim Animal Health France SCS, used under licence.
FRONTLINE PLUS ® contains fipronil and (S)-methoprene. UK: AVM-GSL. FRONTLINE TRI-ACT ® contains fipronil and permethrin. UK: NFA-VPS. FRONTLINE ® SPOT ON contains fipronil. UK: AVM-GSL.
FRONTLINE HOMEGARD ® is a biocide. Use biocides safely. Always read the label and product information before use. Further information available from Boehringer Ingelheim Animal Health UK Ltd, RG12 8YS, UK. Email: petsuk@boehringer-ingelheim.com.
FRONTLINE PLUS ® , FRONTLINE TRI-ACT ® , FRONTLINE ® and FRONTLINE HOMEGARD ® are registered trademarks of Boehringer Ingelheim Animal Health France SCS, used under licence. ©2021 Boehringer Ingelheim Animal Health UK Ltd. All rights reserved. Date of preparation: Mmm 2021. Promomats code.
