How Do Flea Drops Work?

by Sarah | Last Updated: July 18, 2017

If you’ve never used flea drops before, or if you’re a new pet owner, you may be wondering how these little vials work and whether they’re truly effective.

Spot on treatments are a really good option for controlling different types of pests like fleas, ticks and mosquitoes. But, believe it or not, not all drops are created equally.

Because there are so many options, this article will help you get to know the most popular types and how each works to combat insects.

We’ll also talk about some of the common questions that people have regarding this type of flea control.

How do flea drops work?

The drops are absorbed into your pet’s skin and begins to circulate through their sebaceous (oil) glands and bloodstream.

Some treatments work on contact and others work only after the flea actually bites your dog. Different formulas work in different ways, but generally speaking, the poison attacks the insect’s neurosystem and eventually kills it.

It’s important to note that this doesn’t happen instantly. The chemicals will slowly invade the flea’s nervous system, which will cause paralysis and ultimately death. The process can take several hours.

Even though this sounds absolutely dreadful, while the ingredients are very toxic to fleas and ticks, these are mild insecticides and very safe for use on animals.

Differences in Flea Meds

When choosing a spot on flea treatment, it’s important to note there are different types of formulas, and not all work the same.

Some of the most common types are:

Fipronil is used in popular drops like Frontline and Pet Armor. It will effectively kill adult fleas and ticks, but on its own won’t kill flea larvae and eggs. For that, you’ll want to use a combination treatment like Frontline Plus or Pet Armor Plus.

(S)-Methoprene is an ingredient that is often added to meds with Fipronil to aid in killing larvae and eggs. It only makes sense that just killing adult fleas alone won’t help an infestation. By killing the bugs before they hatch or come to maturity, you’re ending the endless breeding cycle and eliminating the pest completely.

Imidacloprid and permethrin is the combination used by K9 Advantix to control adult fleas. These medications work on contact, so the flea never actually needs to bite your dog in order to be affected.

Pyriproxyfen is a third ingredient added to Advantix to control the hatching of eggs and growth of young insects.

Regardless of which formulation you choose, you’ll want to read up on the pros and cons, as well as any precautions that the manufacturer recommends taking before you use them on your pet.

Always, always consult with your veterinarian before you put your dog on any kind of flea regiment – whether drops, pills or collars. Particularly if your dog is on other medications, your vet is your best resource for any health decisions made on your pet’s behalf.

How Do You Apply Them?

Topical treatments are generally applied between the dog’s shoulder blades or at the base of the tail. The reason is pretty simple – these are locations that are difficult, if not impossible, for your dog to reach with his mouth.

When applying drops, go slowly to ensure the drops are actually deposited onto the skin. Just spreading it around on the fur won’t get it into the dog’s oil glands, where it needs to be. Not to mention, you’ll have more of a greasy, oily mess when you’re done!

The following video will show you how to correctly apply the drops:


Once you’re done putting the treatment on your pal, be sure to dispose of the leftover vial in a safe place that your pet can’t reach. You’ll also want to thoroughly wash your hands.

How fast do spot on treatments work?

From the time of application, the drops will spread through the dog’s oil glands within about a day. You may start seeing results in as little as 12 hours, but give the medication at least 24 hours to really start doing its job.

Help Separaation Anxiety in DogsAs mentioned previously, the fleas won’t die instantly when they come in contact with the spot treatment. It will take at least several hours, so know that it will likely take at least a day or so for you to see overall improvement.

How often can you use them?

Only use a topical as directed on the box, which is usually once every 30 days. While the insecticides used in the drops are generally safe, using them too often can literally lead to an overdose.

Based on a study done by the EPA, many negative reactions that pets have had to a flea spot treatment were due to mistakes made by the owner. These could include things like using the incorrect dosage for the pet or giving the medication too often.

When in doubt, consult your vet regarding dosages and how often you should give your dog any medication.

What is the expiration date?

When you look over a box of topical treatment, you’ll probably notice there isn’t an expiration date listed. It doesn’t mean it’s good forever. But, kept under the right conditions, it will stay safe and effective for a really long time.

According to PetArmor, as long as the box is kept in a cool (under 77 ° F) and dry place, you can expect the vials to have a shelf life of up to 5 years.

Are these safe to use on my cat?

Flea Drops & Cats

No. You should never use drops designed for dogs on a cat. Even if you have a larger cat, don’t risk his health by giving him a product not specifically made for him.

Using a dog product on your cat could result in a negative reaction, up to and including death.

Most manufacturers of canine flea control also make a version for cats.

Visit your local pet store, favorite online pet shop or call your vet for more information.

Wrapping it Up

Used as directed, flea drops are a very safe and effective way to combat fleas, ticks and other pests.

As with any medication, make sure you speak with your vet before starting any type of treatment. You’ll want to also keep a good eye on your pet for any signs of a negative reaction. Especially if you’ve never used a product before.

Once you’ve decided on a product, make sure to follow the directions and don’t forget to give the monthly dose! Within a few days, you’ll be on your way to a flea and tick free zone on your pet – and in your home!


Spot On Flea Control