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Why is my cat losing hair after flea medication? Allergic reaction?

Updated On September 23rd, 2025

Pet's info: Cat | Mixed Breed | Male | neutered | 9 years old | 10 lbs

My cat is losing his hair in the place I put his flea medication. It was a new one that I used called Hartz Ulta Guard and he seemed to be having a negitve reaction to it last night so I washed it off his fur however today I noticed the beginnings of a bald spot where the medication was...is it from the flea medication? Is he having an allergic reaction? He still eats, plays and has a regular routine and the hair loss doesn't seem to bother him but it's got me worried. Thanks in advanced.

2 Answers

Most Helpful Answer

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Answered By Dr. Melanie, BVSc MS

Veterinarian

Published on April 10th, 2017

Poor Zero! Unfortunately, Hartz is a very poor brand of flea treatment and it can cause things like fur loss. I'm not a fan of it at all, and I personally never recommend using it. Good on you for washing it off of him. Because he has a bald spot on hi from where the flea treatment was applied, I would not use another spot on treatment on him. Instead, I suggest an oral treatment such as Comfortis. It kills fleas and ticks, and is approved for use in cats. You can get it from your vet's clinic.

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    Answered By Destini R. Holloway, DVM

    Veterinarian

    Published on September 29th, 2019

    This is commonly seen with a lot of your cheaper over the counter flea products. Dottie had a localized allergic reaction to the Hartz and therefore lost her hair. She also was scratching the area b/c it was likely causing a lot of itching, which has now led to scabbing of the area. Because of the location you can clean it with Betadine diluted 50:50 with warm water and yes a very thin layer of Neosporin is ok to apply here. However, if the area does not seem to be improving within a day or two, a vet visit is highly recommended to get her on additional treatment to get this to heal. For the future, I would recommend not using Hartz anymore and instead looking into higher quality products such as Revolution, Cheristin or even Advantage II is ok to try. There is always a chance she could have a reaction to any medication, but there are significantly fewer reactions to these products than others. Best of luck with your pet Dottie moving forward. Take care!

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