The Seresto® Dog Collar: How Does it Work?

If you spend much time outdoors and have a dog or two, perhaps you will agree that ticks are the bane of our existence. They are a constant, ubiquitous threat to our health and sense of well-being. And, to make things worse, their numbers are increasing according to scientists.

Unfortunately, there’s little we humans can do to prevent these dreaded ticks from making their way onto our bodies—we just have to constantly check for them upon returning from our outdoor adventures. And, we keep our fingers crossed we didn’t miss those microscopic nymphs that are all but invisible to the naked eye.

The good news is, the Seresto® collar is an effective tick repellent for dogs—it not only eliminates ticks, but also gets rid of fleas and flea eggs on dogs.

Fellow dog owners rave about the Seresto Collar, claiming it’s more effective than the other flea and tick preventative products they’ve used, especially since it’s practically foolproof. They explain that it’s convenient and not prone to ‘user error’ since it doesn’t involve any messy, monthly topical applications they must remember. And it can last many months before it needs replacing. Many veterinarians recommend it as well.

How Does Seresto Actually Work?

The Seresto Collar comes in two sizes—large or small—and is sized to fit your dog’s neck similar to an ordinary collar. It contains two active, odorless chemicals—imidacloprid (for fleas and their eggs) and flumethrin (for ticks)—which are embedded in the plastic collar and released in low concentrations and distributed over the dog’s body on a sustained basis for up to eight months. These chemicals have been clinically proven to kill fleas and ticks on contact—no bite necessary—within a matter of hours.

The collar starts killing the existing fleas on your dog within 24 hours and ticks within 48 hours, and then kills or repels fleas and ticks within a few hours to prevent new infestations. Remove any embedded ticks from your dog’s skin before putting the collar on—already-embedded ticks may remain attached even after the Seresto Collar has started to work.

Compared to other flea and tick collars on the market, Seresto is longer lasting and continues to work even after it has gotten wet. And it eliminates all fleas and ticks from the dog’s entire body, not just those near the collar. It is different also because it eliminates adult fleas as well as their larvae, interrupting the fleas’ life cycle—which prevents reinfestation and keeps eggs and larvae out of bedding. It works more quickly than competing products, reducing the chance of tick-borne disease transmission. Finally, because there’s no need to remember to reapply Seresto, it’s more reliable than Frontline® and other topical solutions.

Seresto Collars contain the same or comparable chemicals included in other flea and tick treatments such as Frontline and NexGard, but you probably shouldn’t use them at the same time. Experts warn that dual usage poses a risk of overdose toxicity—a serious reaction to a medication overdose. Consult a veterinarian prior to changing or combining flea and tick spot or oral treatments with a Seresto Collar.

The collar is not effective against heartworm infection; your dog still requires an ongoing heartworm preventative, as prescribed by your veterinarian.

How Long Do Seresto Collars Last?

A controlled release of the infestation-fighting chemicals in Seresto Collars means the flea and tick prevention lasts for up to eight months with only one application. That’s easier—and more reliable—than topical treatments you must remember on a monthly basis.

The Seresto Collar works only when your dog is wearing it. Taking the collar off at night, removing it during the day, or putting it on him only when you go outside may decrease its effectiveness, as the cumulative release of chemicals is what keeps fleas and ticks at bay. For the best protection, leave the collar on your dog.

Can the Seresto Collar Get Wet?

We know how hard it is to catch our water-loving canines before they leap into the pond, but there’s no reason to remove the collar for a swim. The Seresto Collar is water-resistant, so it’s effective even if it gets wet. It will continue to repel and kill pests even after your dog goes swimming, is bathed, or gets caught outside in the rain. While water-resistant, it’s not waterproof: It can stand up to a dunking here and there, but repeated water exposure will shorten the life of the collar slightly depending on frequency. The manufacturer suggests that bathing or swimming more than once per month can reduce efficacy to five to seven months. Consult the manufacturer’s product information for details.

There Are Ticks on My Dog—Is the Collar Working?

Because the Seresto Collar works through contact, it’s possible for your dog to pick up fleas and ticks while you’re out on a hike—but the collar repels or kills the bugs before they’re able to bite. You can double up protection by brushing your dog after a walk through grassy or wooded areas.

Is the Seresto Collar Safe?

Veterinarians consider the Seresto Collar a safe preventative against fleas and ticks and not harmful to adults or kids—but the manufacturer’s safety paperwork offers a few precautions.


  • Owners are reminded to wash their hands after handling or putting the collar on their dog.
  • Because the collar includes small pieces that are choking hazards and the plastic is impregnated with insecticides, children should not be allowed to play with, wear, or handle the collar.
  • Adults and children should wash their hands after playing with a pet who is wearing a Seresto Collar.
  • Don’t put the collar in your mouth or allow children to chew on it.
  • Chemicals are contained within the Seresto Collar’s plastic, so contact with the collar isn’t harmful, but chewing on or ingesting it can cause stomach upset, vomiting, lethargy, or a blockage—contact your vet if you suspect your dog has ingested any part of a flea collar.
  • The manufacturer and veterinarians recommend against using Seresto Collars for pregnant or lactating dogs or for puppies younger than seven weeks.
  • The collar is intended for dogs only; veterinarians don’t recommend using Seresto Collars for other animals due to the risk of overdose or adverse reactions.

As a safety consideration, the collar is designed to break off if it gets caught on something while your dog is wearing it. And, it comes with reflectors you can attach to make your dog more visible at night. The Seresto Collar is not meant to replace your dog’s regular collar with ID. Alternatively, you could outfit your dog in the personalized side-release collar to which the Seresto Collar can be attached.

What About Side Effects?

According to the manufacturer, Seresto has been tested extensively for safety. Reported side effects include allergic reaction, lethargy, localized skin irritation, and hair loss on the dog’s neck. The safety information included with the collar indicates removing the collar and bathing your dog thoroughly if any signs of irritation occur. Because some dogs are more sensitive than others and there are many factors to consider, it’s best to consult your veterinarian with any questions or concerns before using Seresto or any other medication.

There is no perfect solution when it comes to finding an effective flea and tick repellent for your dog, but Seresto is a proven deterrent. Its effectiveness is owing in large part to its ingenious design, which makes it especially easy to use. Now if only there were as reliable a way to keep ticks off of humans! Or, better yet, a way to keep ticks well away from all of us.

62 thoughts on “The Seresto® Dog Collar: How Does it Work?”

  1. Love these collars. I have used the others, the pills and the liquid, and wound up picking dead, but still bloated, ticks off of my dogs, which left a hole in my dogs skin. The collars on the other hand, prevent the ticks from ever getting on them to begin with. I don’t understand why anyone would not use them!!

    1. I totally agree! They are wonderful and work great! has the best prices that I’ve been able to find

    2. These collars was a total waist of my money. I bought 2 and neither worked! I bought a small one for my Yorkie and a large one for my German Shepard. Both useless!!

      1. Are you sure you got a real one. The ones from China are fake. You can go on youtube watch the video to see if it’s fake. The real ones are great

        1. I’ve bought the collars at Walmart and there fake every time I turned around my dogs had fleas. Same with advantage 2 for cats, and advantix 2 all bought at wal mart none of them worked. Went to my vet and bought some they worked.

          1. I would only buy from chewy. Com or somewhere dedicated to pet supplies and that does NOT deal ever with 3rd party sellers. This is a risk you take with Walmart even when purchasing direct that merchandise may get mixed up.

            It’s very near impossible to tell a fake from a real seresto collar for the record.

    3. I have pull half bloated ticks from my dog two times on a seresto collar. I buy her a new one before the old is bad. No body can tell me why this happens. both times the ticks where just about her brow bone.
      She can not take the bravecto becasue she had a bad reaction. I am worried she is at risk.

      1. I had that issue when using advantix ii & Bayer advised to apply at 3wk mark. I’m guessing that applying seresto at 6mos or so is probably safer but I’d call Bayer to see – theyre pretty helpful. Usually if not always you speak to a vet who specializes in your product. Might try that.

  2. Yep!! We love the collar as well. Unfortunately my wonderful husband cut the collar too short! He weighs 125. However, we have had luck with them. Our 16 year old daschund wears 1 a year!!

    1. Ugh, Put collar on my lab and 4 live fleas. I am shocked. Any thoughts? It’s been 4 days and all the nessary cleaning and even steaming everything in sight.

      1. It may not be effective if it is not on tightly enough. Do not leave more than a snug 2 fingers under the collar. I must be against the skin.

        1. There are a LOT of fake collars on the market – they are indestinguishable and ineffective. Buy Seresto only from places like chewy. Com & 1-800-pet meds where they purchase direct from manufacturer. If you get from Walmart and Amazon or worse ebay it’s easy to get a knock off.

      2. Add K9 Advantix to your treatment. Same manufacturer as Seresto no conflicts within the 2 Bayer products. Both are manufactured by them

  3. I have been using this particular collar for 4 years. Unfortunately the new one I purchased about a week ago is not working. My dog has fleas( insert catchy tune). I have never had this problem in the 4 years of using this product. I know it’s the name brand as I purchased it at the same store I always do. Now I have to deflea my home and I’m not happy at all. I also plan to contact the manufacturer to let them know this collar failed me 🙁 Before this I would recommend this brand to everyone I knew with a cat or dog.

    1. Just want to let everyone know, I love Seresto is awesome. It really does work, however there is a bait and switch scam going on . They claim you can get seresto for half price but if you look closely at their ad, it says seresto with a circle with an R in the middle, I think that is a patent stamp. But beware, some places in the ad, they actually have the nerve to use the correct spelling, the company doing this is manybel,and they will get rich before my message gets to all those dog lovers out there, If you try to get your money back,they tell you to go to [email protected], which never opens, if you try their phone number you get a recording. They have a charge for “restocking”, a percentage for their trouble and they will make you pay for shipping. If yours comes in the mail after you read this, I would return it unopened(that way you don’t pay for postage) but, if it has been opened, stick a note inside telling them you want a complete refund because they did not hold up their end of the contract to buy,and send it back, call your better business bureau, good luck to you all. Hope you get this on time. Are you sure it is the real Seresto, not the fake one made by manybel?

    2. I’m having the Sam problem. The first few I bought were great, no fleas. The last 2 haven’t worked as well. Any suggestions?

    3. Same here, I bought 4 online from Walmart, 2 weeks later all for pets have fleas last year they worked great!

      1. how to tell if knock off , On the bottom tin, a Seresto collar is replicated, with reflectors attached, around the tin. The back label is not a label, and there’s a lot number that matches the lot number on the collar itself. If either lot number is missing, it’s counterfeit product. If the collar is packed in a foil packet, it’s fake.

    4. Same here the collar is on correctly and I bet I got over 50 fleas off of him in the bath.. I am totally disgusted and will not buy again.. nor will I recommend to my customers as I have in the past. I am not a happy fur mom

      1. I’m having same problem. Past collars have worked great. Now my dog still has fleas. Could it be fleas developed immunity to it?

      2. Perhaps buy one from your veterinarian office. There are a lot of scams going on with these collars. I was scammed once then I bought all six of my pets one from my vet and they worked as stated. Best most effective flea treatment ever.

  4. I had the same result. Used it successfully on my former dog, but this time the fleas seems to be attracted instead of repelled. Just had a terrible infestation with my sweet little rescued Poodle/Maltese.
    What do I do now?

    1. I have been a huge fan of the collars the last two years. Recently I bought 4 collars for my German Shepherd’s. None of the collars are working.
      I am pulling off live fully engorged ticks everyday, the ticks are feasting, causing the usual redness, oozing & long lasting bite mark. The ticks are not dying or being repelled like previously. Something has changed. Right now I would not recommend using them.

      1. I am a first time user with the collar…my dog doesnt seem to have fleas but we saw 2 ticks on her today not sure why it didnt repel them or how its supose to work with the ticks.

        1. Sweetie the seresto say on Google that if a ticks get on your dog in matter in hour’s it kill the tick the seresto that the dog wear it go over the hole body of the dog so when tick bites it won’t last a long time on your dog. It can get wet in lake if want to swim and get bath or out in the poor rain. Tjis is what it say ask questions on Google on this and i found two on my dog no fleas yet. Hope this help you out and you can ask the vet too.

    1. It may not be effective if it is not on tightly enough. Do not leave more than a snug 2 fingers under the collar. I must be against the skin. Call Bayer Healthcare, LLC, 1-800-255-6826.. They will answer and discuss all questions and give your pet a case number to follow your pet’s situation.

    1. Do not buy the cheaper one made by Manybel? There is a scam going on, it is the old bait and switch, just read my post above

  5. Love these collars. Had an infestation and started using Seresto collar along with washing all bedding and daily vacuuming of the floors and upholstery. It took several days for all fleas to be effected on the dogs.

    For those who have had flea infestations, it takes a full 90 days of treatment inside the house to fully get rid of the fleas and break the lifecycle. All the fleas are not on the dog!!! If your dog has fleas your entire house has fleas.

    I have never had a tick problem using this collar. We live in Florida, so fleas & ticks are a huge problem.

  6. I love these Collars. So far they have worked on my two Shih Zui wonderfully!! Im so excited because nothing I tried seemed to work. They were chewing on themselves till they were bleeding. I felt so bad for them. My babies are highly allergic to fleas and I’m so glad the clerk at Petsmart told me about them. I had gone in the store getting what I always use and they were out if it so the clerk told me about how all her customers that use these collars swear by them. I will recommend them to everyone. I just wish they weren’t so high. I feel $50 is a fair price but my babies are worth the price I paid.

    1. I recently bought seresto collar from Chewy. Not fake. I bathed my shitzu 2 weeks later and I got blobs of fallen hair in my hands from tail to neck. I couldn’t believe it. I stopped using it. He’s allergic to nexguard.. seizures.

  7. These collars work very well on fleas but it takes a few weeks to break the flea cycle. Best product yet for flea control.

    1. i buy mine on chewy or amazon
      there is a way to tell if its fake : On the bottom tin, a Seresto collar is replicated, with reflectors attached, around the tin. The back label is not a label, and there’s a lot number that matches the lot number on the collar itself. If either lot number is missing, it’s counterfeit product. If the collar is packed in a foil packet, it’s fake.

  8. Have had on my dog for 3 weeks and had it on before the tick season got going good and was very disappointed to find 10 – 12 ticks attached to my dog today. $70 is too much for my dog to still have tick bites.

  9. Mine is not working either. Pulled off 6 dog ticks and 2 deer ticks and have had the collar on her for 4 weeks.

  10. My dog has fleas too. This is our second collar. The first worked great!
    Is there something we can do to get another that works?????

  11. My last 2 seresto flea collars have Not worked ? A huge waste of money.. can’t see wasting any more money on them as their Overpriced anyway

  12. Does it matter if u put a flea collar that met for a large dog on a small dog weighing 10 pounds, will the collar hurt the small dog. Or are they all the same. Except large collar is bigger an has to be cut to fit a smaller dog, otherwise will it be safe

  13. We purchased our dog’s collar in May and so far she still has fleas. The last collar she had worked right away so I’m not sure what is different this time. Very frustrating to pay $50 and have it not work. I’m going to try and call the number that someone else posted and see what they say.

  14. It has been over two weeks since I ordered the collar and still have not received it yet. Tried calling the number just a recording as well. Why is it the FB puts these adds on here without doing the research first to see if they all legal or not.

  15. I absolutely won’t turn back to what I used to use on my dogs.
    This collar is the best, best best ever.
    Please beware of folks trying to sell fake collars on line, if it sounds too good to be true it actually is.
    Have been taken for one of the offers.
    Yes you will have to dig deep into your pocket to purchase one of Seresto collars but it’s well worth it.
    There are great you tube videos to find out what you should look for to keep you from buying a fake collar.

  16. The Seresto collar worked really for us (in an area with a very heavy tick population). Unfortunately, our dog developed a sensitivity to it (hair loss under her neck and red itchy skin) and now we’re on the hunt for something else.

  17. The seresto collars that I bought in March 2019 at the veterinary office. Put them on my 2 dogs and the end of july we ended up with fleas and we are still fighting with fleas the middle of August. Let me know what I’m supposed to do now they have no experation date on the collars. 76 dollars down the drain. I have fogged my house, washed everything, vacuumed, flea baths. My dogs and I are going crazy.

  18. I’m sorry but your 8 month collars don’t work. We got three for our dogs. Fleas never went away and they became infested . They are on something different now and at 1/8 of the cost….. what a disappointment

  19. I’m having same issues also, not working the last 2 years like they used to. I called Bayer, if you still have your cans you can have them check the lot number to see if they are counterfeit. I have been bathing dogs every week to get rid of fleas, she told me limit baths to once a month with oatmeal shampoo so you don’t strip natural oils from dogs coat, the oil is necessary to transport flea killing product. ..I’ll give it a try…..

  20. I have sorresto collars on my 3 dogs.
    My 10# doxiepin,and my bigger dog a catahula, and both have hair issues afterwards, moreso my bigger dog’s hair became thin & fell out.
    My 35# pomeranian doesn’t have the issue as the other 2 not sure why.
    Can the sorresto collars cause hair thinning & hairloss,especially around the collar area?
    They have no fleas,yet scratch,so the collars work.
    Is this common,or an allergic reaction to the collars?
    I’ve used before with the 2 bigger dogs,yet still same issue with hair loss in the one.
    My big dog lost hair at collar area,base of tail & mid tail,chest (chest area may be from her pulling on her harness, she wears harness all the time).
    Doxiepin hair thinning collar area,on his ears,and his chest (chest area may be from where he pulls on his harness, he wears harness all the time).
    Pomeranian doesn’t have the hair loss,or hair thinning like my other 2 not sure why.
    The collars work,just hair loss on 2 of the 3 dogs.
    Can you offer me some insight on this & get back to me on this issue we’ve been having?

  21. There is not a perfect solution…. but….we live in a wooded area (in NY Sate) with lots of ticks and some Lyme cases both dogs and humans. We have found that Seresto is a lot more effective than other tick collars or drops. Yes we do find the occasional embedded tick on our dog, sometimes right beside the collar. However the # of embedded ticks a year is probably 60% lowers using a Seresto collar.

  22. I recently bought seresto collar from Chewy. Not fake. I bathed my shitzu 2 weeks later and I got blobs of fallen hair in my hands from tail to neck. I couldn’t believe it. I stopped using it. He’s allergic to nexguard.. seizures.