4 Signs Your Pet’s Flea Medication Isn’t Doing the Job

black and gray striped cat sitting on a low stone wall in a yard, scratching its chin

If your pet were a superhero (Wait — who are we kidding? Your pet IS a superhero!), there’s no doubt that fleas would be their Kryptonite. Left uncontrolled, those nasty little buggers torment our dogs and cats with their itchy bites, causing them to scratch and chew themselves silly — often leading to open sores and secondary infections. Fleas can also spread dangerous diseases such as murine typhus, tapeworms and cat scratch disease (yes, that’s a real thing!). And since we humans aren’t immune to their annoying bites, keeping them under control is as important for us as it is for our pets.

Given the havoc fleas can wreak on both pets and their humans, the need to keep them protected year-round goes without saying. That’s why we give them regular doses of a veterinarian-recommended flea preventative each month — right…? But what if the medication you’ve chosen isn’t working properly? Or what if your pet is having a negative reaction to the medication? How can you tell?

Here are four signs that your pet’s flea protection may not be doing the job — and what you should do about them.

1. You’re still finding fleas on your pet
Well, this seems fairly obvious, right? If your pet still has fleas after you’ve given them their medication, it must mean it isn’t working, right…?

Not necessarily.

Fleas can lay up to 40 eggs each day. Multiply that by the number of fleas on your pet, and that number can add up quickly! Each egg can take up to 8 weeks to hatch, so if it took even a day or two for you to notice the fleas crawling on your pet, there could be thousands of eggs scattered on them, around your yard and in your home. For that reason, if you’re just starting your pet on a flea preventative, you need to give it time to work. Treating your home and yard to rid them of fleas and eggs is also important.

However, if your pet still has fleas several weeks after starting a new treatment — or if you’ve been using the same treatment regularly and fleas suddenly start appearing — there’s a chance the medication you’ve chosen isn’t effective, which means it’s time to find a vet for a consultation.

2. The itching won’t stop
You’ve given your pet their meds, and you don’t see any fleas, but they won’t stop chewing and scratching — what then? There are several possibilities in this case — including a negative reaction to the flea medication. That’s why it’s important to reach out to your vet as soon as possible to schedule an exam so they can figure out what’s causing the issue.

3. You start noticing bald spots
There are several causes of hair loss in pets, including allergies, parasites, disease, and adverse reactions to medication. And while the symptoms are unpleasant, the underlying issue can be serious, which is why if your pet starts developing bald patches, it’s important to call your vet right away.

4. Your pet isn’t feeling well
The two most common insecticides found in flea preventatives are called pyrethrins and pyrethroids. Pyrethrins are natural compounds derived from a plant in the chrysanthemum family, while pyrethroids are synthetic chemicals developed in laboratories that tend to last longer. Unfortunately, some pets can have an adverse reaction to these chemicals, especially those who are young, old or sick. Symptoms of pyrethrin and pyrethroid toxicity range from hives, itching, vomiting and diarrhea to depression and muscle tremors, and the consequences can be serious. If your pet develops any of these symptoms, call your vet immediately.

Controlling fleas can be a difficult proposition, which is why it’s so important to consult your vet before starting your pet on a preventative medication. Your doctor will have the latest information on which medications are most effective in your area, as well as safe, practical ways to treat your home and yard to help keep fleas at bay year-round.