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Dog has a red lump under armpit, doubled in size. Should I see a vet?

Updated On September 23rd, 2025

Pet's info: Dog | Mixed Breed Small (up to 22lb) | Male | neutered | 3 years and 4 months old | 17 lbs

I noticed a red lump under my dogs armpit about a week ago. I’ve been monitoring it and today when I got home from work I noticed it had almost doubled in size. He has been licking his armpits a lot recently, even before the lump appeared, so wondering if the development and growth of the lump could be due to the licking of the area? Is this something I should just continue to monitor or should I take him to my vet?

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2 Answers

Most Helpful Answer

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Answered By Dr. Melanie, BVSc MS

Veterinarian

Published on May 1st, 2018

Thank you for contacting Pet Coach with your concern about Finn! Yes, this is definitely something I would have him seen by a vet. It's concerning that this lump has doubled in size in a week, and it's obviously bothering him because he keeps licking at it. It could be this lump is a cyst, a benign tumor, or a malignant tumor. This area also could have formed from irritation of him licking at it, leading to this raised and irritated area. Give your vet a call today to make an appointment, and I would put an Ecollar on him to keep him from licking at it further. You can make one at home (I will put a link below on how to do it), or you can buy one at a pet store. Best of luck, I hope this helps! http://dogsaholic.com/care/homemade-dog-cone.html

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    Answered By Dr. Heidi DVM, CVA, CCRT, CVTP, CVSMT, CVCH

    Veterinarian, Certified Veterinary Acupuncturist, Certified Canine Rehabilitation Practitioner

    Published on

    Anytime a mass quickly enlarges, it should be evaluated. Yes, licking at a mass can cause it to enlarge if it becomes inflamed or infected, but we need to make sure that is why it is enlarging. There are benign masses that we can see in young dogs called a histiocytoma ( https://www.vin.com/veterinarypartner/default.aspx?pid=19239&id=4952066 ) , but we need to make sure that it is benign before we just monitor it. Unfortunately, we can't tell anything about a mass by just looking at it. Your vet can perform a simple test called a fine needle aspirate where they use a small needle to collect some cells from the mass, then look at them under the microscope. They may even need to send the cells to the lab for a pathologist to examine them, so we know what the mass is. If it is benign, you might not need to do anything about the mass at all (unless it is infected or bothering Finn), but if they see cells that worry them, they might recommend removing the mass. Good luck! I hope that was helpful. Thanks for using PetCoach.

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