How different chemical flea and tick preventatives and treatments work

How different chemical flea and tick preventatives and treatments work

Anyone who owns a dog or cat will know that it is important to protect their pet against fleas and ticks, two parasitic organisms that can make your pet uncomfortable, irritated and even ill. Fleas and ticks are also highly unselective when choosing their host, and fleas or ticks on your dog or cat will soon consider a migration to yourself and your human family!

Most of us use a spot-on treatment product to repel and kill fleas and ticks, or possibly a flea collar, spray or other method. But what all of these products have in common is the presence of a chemical compound that impregnates the skin, repelling parasites and killing those that are present.

However, there are a great many different types of chemical flea and tick treatments, and some people find that some of these are more effective for their own pets than others. If your product of choice doesn’t really seem to be up to the job any more, it is worth considering an alternative. In this article, we will cover some of the most common forms of chemical flea and tick repellents and eradicators, so that you can establish which one you currently use and review potential alternatives. Read on to learn more.

Selamectin and Fipronil

Both Selamectin and Fipronil are synthetic chemical compounds that prevent fleas and ticks by blocking the nervous system of the parasite’s ability to transmit chemical signals, ultimately leading to paralysis and death. These chemicals are generally mixed with a carrier oil in a spot-on treatment, which provides adhesion to the skin and enables the slow release of the relevant chemical.

Selamectin is also absorbed through the skin into the bloodstream, where it can also have a positive effect on intestinal parasites too. Fipronil does not do this.

Common spot-on products including Effipro, Frontline, Frontline Plus and Frontline Combi all contain Fipronil, in some cases in conjunction with another ingredient, Methoprene.

Selamectin is present in spot-on treatments such as Stronghold, and Revolution.


Pyrethrins are a group of repellent insecticides from the Pyrethrin group. Pyrethrins work on the nervous system of parasites, disrupting the nerve impulse chains of the pest, which results in their death. Pyrethrins are actually a naturally occurring chemical that is extracted from the flower of the chrysanthemum plant, and are also effective on bugs such as lice and mites. They are low in toxicity to larger animals, which means that they can be applied directly to the skin.

Synthetically produced chemicals that have the same action as Pyrethrins are called Pyrethroids, and these are widely manufactures for use in flea and tick repellents. They have a longer lasting action than natural Pyrethrins, and are usually contained within an oil carrier for spot-on use. They are more common within flea and tick products for dogs than cats, as some cats are sensitive to synthetic Pyrethroids.

Pyrethrins are a common ingredient of most flea sprays, some flea bombs, and household flea treatments.

Organophosphates and Carbamates

Organophosphates and Carbamates are two different compounds that work in the same way; by inhibiting the enzyme function of the nervous system of the parasite, repelling it and killing those already on the skin. They can also be used in combination with Pyrethrins, to lengthen their period of effectiveness.

These two compounds are the two most commonly used in flea collars, and some sprays.


Amitraz is another chemical that is commonly used in tick collars, and is also part of the cocktail used to treat infestation with mange mites. While it is effective for both ticks and mites, it has no action on fleas. Amitraz-containing products are suitable for dogs only, and should never be used for cats.

Linalool and D-limonene

Linalool and D-limonene are two products extracted from the pulp of citrus fruits, which cause an adverse reaction in the nervous system of the parasite, repelling it. These naturally sourced products are rather less toxic than other options, but this also means that they can be less effective. They can be found in sprays, dips and shampoos, and are mainly used for dogs rather than cats, as cats can be very sensitive to these ingredients.

As you can see, while all of these products perform the same task, some are more suitable for some roles than others, and specifically, some products should not be used on cats. Any flea or tick treatment product may potentially lose its effectiveness over time, either on specific animals, or in certain areas of the country where parasites have built up a resistance to it. This means that if your current flea and tick prevention protocol is not working, you will likely need to consider moving onto something else with a different action, or a different active ingredient.

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