How Do Flea & Tick Drops Work?

Flea and tick drops get into your pet's sebaceous system and kill the flea or tick when they bite your dog.
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Flea and tick drops, sometimes called spot-on treatments, protect your dog for 30 days with a single application. These products work when the flea or tick bites your dog ingesting the chemical that has spread throughout your dog's skin glands, thereby providing full-body protection from insects.


Most flea and tick drops come in the form of capsules containing an oily liquid that you place onto your dog’s skin, either between the shoulders or at the base of the tail. The compound soaks through the skin quickly, and is usually waterproof to prevent you from accidentally washing it away. Once in your pet’s body, the agent becomes part of the sebaceous system, the series of glands that lubricate his fur with oil. A short time after dosing your dog, each drop of oil in his coat will contain some of the pesticide.

Nerve Agent

While each spot-on treatment has its own unique chemical base, they all work in a similar fashion. These pesticides attack the nervous system of fleas and ticks, disrupting the natural flow of impulses from cell to cell. This causes the pests to lose control of their bodies, becoming hyperactive and uncoordinated and losing the ability to feed on your dog. The pesticide eventually shuts down their internal organs and kills the pests, usually within 24 hours of the first application.

Growth Inhibitor

Some flea and tick drops also contain a growth inhibitor to deal with flea and tick eggs. Since these eggs are almost impervious to attack, the embryonic parasites inside may survive the initial pesticide dose. The growth inhibitor interrupts their natural development, preventing them from reaching adulthood to lay their own eggs, shutting down the life cycle of the pests. In combination with the nerve agent, this will wipe out fleas and ticks in your dog’s fur as well as prevent new infestations from taking hold.


While the amounts of pesticides used in these products are too small to affect dogs in the normal course of events, they are still dangerous substances and you should handle them with care. Always choose a product tailored to your pet’s species, and do not use cat products on dogs. Weigh your pet before purchasing a dose, and choose the dose best suited to his current size. Do not attempt to estimate or combine doses, because too much of the product could make your dog sick. Finally, do not apply the product more frequently than the instructions call for, as it could lead to an overdose due to the length of time the compound stays in your dog’s system.