Do Fleas Have to Bite for Comfortis to Work? {Is it Better Than Capstar?}

Are you wondering how Comfortis is going to get rid of your flea problem? Do Fleas Have to Bite for Comfortis to Work?

Can Comfortis work like spot treatments or does this oral medication need a flea to ingest it after it bites? Is Comfortis better than Capstar?

In this article, we’ll discuss the topic of using Comfortis to kill fleas and if these pests need to bite for this product to actually work.

Do Fleas Have to Bite for Comfortis to Work?

Yes. Unlike topical treatments, a flea will have to bite into the skin and ingest the active ingredient of Comfortis (Spinosad) located in the bloodstream of the host to die.

How Quickly Does Comfortis Start Working?

Comfortis contains an active ingredient called Spinosad to kill fleas. An oral dose is required for Spinosad to enter the bloodstream.

Once ingested, the dose will begin to work in 30 minutes. The product requires fleas to actually bite the skin for the pest to ingest Spinosad and die from it. The claim is that:

  • It starts working within 30 minutes.
  • 98% of fleas on cats die within 4 hours.
  • 100% of fleas on dogs die within 4 hours.
  • It works for 28 days following a single dose. 

Will Comfortis Kill Fleas in the House?

Fleas are usually transported by the hosts who reside in your home. If you wish to kill these fleas, you will have to stop them at the source.

The pets or humans who are experiencing flea bites will not have to deal with it any longer. Comfortis is going to bite the host and die once ingesting the active ingredient in it known as Spinosad.

Fleas will die before they can lay their eggs and accumulate to the point of becoming a nuisance. You should also set flea traps with dish soap and water near a light source to attract fleas and drown them.

You cannot sprinkle Comfortis around the house because it is meant to be orally ingested.

How Does Comfortis Work?

Comfortis is meant to be taken as an oral dose every 28 days. It contains a safe to ingest insecticide known as Spinosad.

This active ingredient interrupts receptors that are located in a flea’s nervous system. It paralyzes fleas and kills them swiftly.

The only catch is that the host needs to be bitten by the flea for the insecticide to be transferred into the flea in order to kill it.

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Do Fleas Need to Bite for Advantage to Work?

The difference between a product like Advantage compared to Comfortis is that Advantage only requires direct contact from the flea to kill it.

Your pet doesn’t need to be bit for it to work. This is the opposite of oral tablets like Comfortis or Capstar that need to work after the flea ingests some of the insecticide located in the bloodstream of your pet to work.

Can I Crush Comfortis?

Comfortis is an oral tablet that some people may find difficult administering to their pet in one solid dose. The easier solution for some people is to crush it.

The pills are meant to be chewable, but they can also be crushed if you wish. The trick to getting your pet to swallow a pill depends on your relationship, trust, patience and routines.

There is no fail safe method to get your pet to ingest a pill. Crushing the pill and adding it to a meal or treat is one option.

Does Comfortis Repel Fleas?

Repelling fleas works better by setting flea traps. You will only need dish soap and water with a light source near it to attract fleas and cause them to drown inside the trap.

Comfortis needs the host to attract the flea and bite the skin. Once they do so, they die.

This means that Comfortis can claim to prevent future infestations or keep fleas from laying their eggs.

Do Fleas Have to Bite for Capstar to Work?

Capstar needs to be swallowed in order for the active ingredient known as nitenpyram to get into the bloodstream.

The host will carry this insecticide in its blood and become lethal to a flea when it bites the skin.

The insecticide is deemed safe for cats and dogs while completely killing off fleas who need to bite and ingest the active ingredient in Capstar to die.

Is Capstar or Comfortis Better?

Capstar and Comfortis are both oral doses to kill fleas once they bite the host. Here are some key differences:


  • No prescription needed by a vet
  • Works for 24-48 hours
  • Claims to kill 90% of fleas within 4 hours


  • Prescription needed in most countries 
  • Works for 28 days after a single dose
  • Claims to kill 98% of fleas in cats and 100% in dogs within 4 hours

Based on the information and availability, you can decide which is better for your flea situation.


Comfortis is meant to be ingested orally and claims to be effective with just one monthly dose. We find it inconvenient to obtain a prescription from a vet to use Comfortis when a similar product like Capstar is more widely available.

We like a product like Advantage that kills fleas on contact or flea traps and flea baths with dish soaps compared to Comfortis for one reason: Your pet doesn’t need to be bitten in order for the fleas to die.

This is the only way Comfortis is going to work, but the treatment is effective nonetheless.


Thanks for visiting for the best information to help you to make the pest control process easy, safe & affordable. 

Jason Barrett

Hello, I'm Jason. I have 11 years of experience in dealing with pests. I try to provide you the best information that'll help you to make the pest control process easy & affordable