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What serious health problems can untreated fleas cause in cats?

Updated on September 23rd, 2025

Pet's info: Cat | Mixed Breed | Male | neutered | 20 lbs

What problems can fleas cause in cats if left untreated?

3 Answers

Most Helpful Answer

Destini R. Holloway, DVM

Answered By Destini R. Holloway, DVM

Veterinarian

Published on June 7th, 2017

While fleas may simply seem like a nuisance, the reality is that they can pose serious problems. Heavy flea infestations, particularly in very small animals, can result in significant blood loss, which causes potentially lethal anemia. Fleas can also transmit a variety of diseases, including cat scratch disease (*Bartonella henselae*) and tapeworms (*Dipylidium caninum*). Many pets are allergic to the saliva injected during a flea’s bite, and can develop severe itching, hair loss and skin infections.

Fortunately, most cases of fleas can be both treated and prevented at home with the consistent use of good-quality flea preventative medications. It’s important to remember to use a flea preventative that is labeled and safe for cats. Some flea preventives for dogs are not safe for cats. Some examples of over-the-counter products that are labeled for cats include Cheristin for Cats, Capstar for Cats, Advantage II, and Frontline Plus for cats. Other products such as Comfortis for Cats, AdvantageMulti for cats and Revolution for cats are available with a prescription from your veterinarian. However, more severely affected cats require evaluation and treatment by a veterinarian.

If left untreated, flea infestations in cats can also impact human health with the possibility of spreading cat scratch disease, plague or typhus. Ultimately, it is best to avoid fleas altogether with the regular use of a good quality flea preventative medication.

### Cheristin is a trademark of Elanco or its affiliates.
Vote Icon154Pet Parents found this answer helpful

Related Answers from Veterinarians

  • Answered By Sabina Snyder, Specialty Surgery Technician

    Veterinary Technician

    Published on September 24th, 2019

    It really depends... some over the counter flea medications can cause allergic reactions. This could be what is going on. I personally never recommend using anything you can buy at the store/Petsmart/etc for cats because most of it contains pyrethrin which is an actual insecticide. It can be highly toxic.
    I always recommend getting flea control from your vet for two reasons:
    1. You know its safe. Manufactures guarantee their products when they are purchased at a Vet. They don't when they are purchased elsewhere.
    2. You can get better options. Your vet will carry things like Revolution, which not only protects against fleas, but also ear mites, intestinal worms and heartworms, which can be fatal to cats!

    If this issue persists, or gets worse, please go see your vet right away. If you are concerned that the product you used may have harmed your cat, give him a bath with Dawn dish soap.

    Good luck and feel free to consult with me privately if you have any follow up questions or concerns!

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    1Pet Parents found this answer helpful

  • Answered By David Darvishian

    Veterinarian

    Published on November 8th, 2017

    Hi and thanks for using Petco Pet Education Center, formerly Petcoach! Great question. Enough fleas on a kitten combined with intestinal hookworms which suck blood can definitely cause great harm to a kitten including death from anemia (low red blood cell count). Fleas suck blood to reproduce and in addition, if hookworms are present, a kitten can develop a life-threatening anemia due to blood loss. Fleas can also be a source of devastating bacterial infections which can cause zoonotic disease in humans and in cats. It is always highly advised that you keep an effective flea and/or tick medicine on your cat to prevent flea infestations from taking hold on your cat and thus in your environment. Good luck and remember to consult with your veterinarian to discuss adequate external parasite control in your geographic location

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    1Pet Parents found this answer helpful

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What flea diseases cause cat lethargy, fever, and anemia symptoms?
Hi there and thank you for using Petco Pet Education Center, formerly Petcoach to address your concern. There are several diseases that you can see transmitted from fleas to cats. Tapeworm, Tularemia, Feline infectious anemia, Cat scratch disease and anemia to name the most commonly seen.
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How to effectively treat cat fleas and prevent them from returning?
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How do I get rid of severe cat fleas infesting my cat and home?
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Could flea and tick treatment cause anemia in my senior cat?
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Should I worry about my cat's severe fleas, scabs, and hoarse meow?
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My cat has fleas and a swollen foot wound. What's the best treatment?
That wound on his foot looks swollen which is concerning for a deeper infection or a wound to the bone structures in the leg. I recommend to get this examined since a physical exam is the first step in determining the extent of the injury. As for the fleas, top products for cats are topicals such as Revolution and Cheristan. There is also an oral product called Comfortis that both dogs and cats can take. You will need to switch all the pets over to a good flea product. Make sure to discuss these products with your veterinarian first. These products are generally safe for all pets but there are some conditions which are contraindicated for the oral products. Cleaning up and treating the house and yard will also help but it will not clear all the fleas. The main control is making sure the pets are on good products. This is what will ultimately stop the infestation. Also remember every female fleas lays about 50 eggs a day and it could take up to 6 months before the eggs hatch. Therefore, you will need to treat for at least 6 months. Best of luck and please feel free to post any additional questions.
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How to treat severe cat fleas when her neck is scabby and irritated?
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