How Do Flea & Tick Treatments Work on Cats and Dogs?

For many pet owners, fleas and ticks are a year-round concern – they celebrate all seasons and are always on the lookout for their next meal.

As these ectoparasites evolve to resist our methods of combatting them, new products are continuously developed. It then becomes a balancing act of sorts, as responsible pet parents seek the best ways to prevent and kill these pests while keeping their four-legged friend’s well-being in mind. But how exactly do topical drops, collars, sprays, powders and shampoos control flea and ticks on our cats or dogs?

Types of Flea & Tick Control Products and How They Work

Aside from posing a nuisance, fleas and ticks have the potential to transmit numerous types of diseases to both animals and people. To reduce putting your pet and your family at risk, use medicated drops, collars, powders, shampoos or sprays to keep pesky parasites at bay. Remember to only use these products as instructed, and consult your veterinarian if your cat or dog experiences any adverse reactions.

Topical Drops:

Liquid medications, sometimes called spot-on treatments, are applied directly to a cat or dog’s skin, usually between the shoulders, at the base of neck (for cats), or along the entire back from the base of neck to tail (for dogs). These products come in the form of vials that contains agents which protect your pet for 30 continuous days.

Fleas in a dogs coat. Learn about dog flea and tick treatment and how it works.

Fleas and ticks have the potential to transmit numerous types of diseases to both animals and people.

They work by killing fleas and ticks (and sometimes mosquitos, depending on the product) by depositing chemicals into the sebaceous glands, where the active ingredient is released and translocates through the glands that lubricate a cat or dogs coat with oil. When applied, the compound quickly translocates across the skin. The pesticide will attack the flea and tick’s nervous system and cause the parasites to lose the ability to feed on your pet.

Some flea and tick drops also contain an insect growth regulator (IGR) to control eggs that may have survived during the initial dosing. IGRs prevent the development of the eggs from reaching adulthood, thus disrupting the natural lifecycle. IGRs also prevent new infestations.

Flea and tick drops are very convenient to use and continue to work even if your cat or dog is bathed or gets caught in the rain.


  • Always choose a flea and tick drop that is made for your species of pet
  • Weigh your pet to ensure you purchase the correct dose suited for his or her size
  • Do not combine doses, apply the product more frequently than instructed or mix with other flea and tick products, as it could lead to an overdose
  • For best results, do not bathe your pet 24 hours prior to or after application


Flea and tick collars are a convenient option for pet owners with cats or dogs that are not suffering from an existing infestation. Like topical formulas, they effectively prevent but will not necessarily cure an infestation.

Collars have a longer lasting efficacy, typically up to 7 or 8 months, and can be worn in addition to a pet’s normal collar. Flea and tick collars have two functions: repelling and treating. Some collars only repel and others both repel and treat.

Repellant collars emit a gas that deters fleas and ticks from biting. Treatment collars contain medication that is absorbed into the sebaceous glands and spread using the natural oils in a cat or dog’s skin. If only using a collar that repels, a parasite must bite for the pesticide to kill it. Treatment collars release ingredients that kill fleas and ticks on contact before they bite.

Hartz® UltraGuard Plus® Flea & Tick Collar for Puppies
Hartz® UltraGuard® Reflecting Flea & Tick Collar for Cats and Kittens

Be sure to read the packaging clearly of any flea and tick collar you’re considering to be sure it addresses all your concerns.


  • Always choose a flea and tick collar that is made for your species of pet
  • Measure your pet’s neck to ensure the collar is suited for his or her size
  • Do not combine doses, apply the product more frequently than instructed or mix with other flea and tick products, as it could lead to an overdose

Oral Pills:

Oral flea treatments are typically only available by prescription from a veterinarian, and come in both pill and chewable forms, which are ingested by your pet as opposed to being applied to the body.

Oral insecticides typically target either flea eggs or adult fleas, but not both, so you may have to choose which part of the lifecycle to target and eradicate. Flea pills work very quickly, beginning in as little as 30 minutes.

Currently, there are no oral medications that kill ticks.

Powders and Sprays:

Spray-on as well as powder form flea and tick treatments are applied directly to your pet and then massaged into the fur on the entire body. They can be used more freely than other types of protection, and also come in versions which are designed to be used in your home on upholstery, carpets and bedding to protect the entire environment of your pet and your family.

Powders and sprays work well for cats and dogs of all life stages, making them very versatile. Take care to protect the eyes and ears of your pet when applying.


Flea and tick shampoos primarily kill fleas and ticks that are already on a pet, through contact. To properly use these products, wet your pet's coat thoroughly with water and rub the shampoo into the coat, ensuring not to get suds into the eyes or ears. Massage from head to tail until the coat is completely covered with a foamy lather. Let stand or continue to massage for several more minutes. Rinse and towel dry.

Most formulations can be repeated weekly.