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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?

5 Answers

Most Helpful Answer

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

5Pet Parents found this answer helpful

Related Answers from Veterinarians

Answered By Dr. Heidi DVM, CVA, CCRT, CVTP, CVSMT, CVCH
Veterinarian, Certified Veterinary Acupuncturist, Certified Canine Rehabilitation Practitioner
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.
4Pet Parents found this answer helpful
Answered By Lauren Kennedy, DVM
Veterinarian
Published on March 8th, 2018
The mass you have pictured appears benign. I don’t think this is the cause of the other symptoms you have mentioned.

Since her behavior has changed so drastically and she is an older dog, I would recommend taking her to the vet to be examined. It would be wise to have some lab work performed as well.

The excessive licking could be due to allergies (itch) or pain. A thorough examination by your vet should help determinw between the two.

I hope this helps. Thanks for using Petco Pet Education Center, formerly Petcoach. Best of luck.
1Pet Parents found this answer helpful
Answered By Megan, DVM, CVA
Veterinarian
Published on December 23rd, 2017
Poor Jarvis. I looks infected and like he has been licking it. I would make sure he isn’t licking it. You can put a cone collar on him to prevent this. You can try to put neosporin on the area and give him Benadryl twice a day. See link below. If you aren’t seeing any improvement or if it begins to swell I would ha e your vet take a look at it. Your vet will be able to make sure there isn’t anything stuck in it. Your vet will also be able to start him on antibiotics and an anti-inflammatory if needed. I hope this helps.

https://www.petcoach.co/canigive/dog/benadryl/
2Pet Parents found this answer helpful
Answered By Daniel Fonza, DVM
Veterinarian
Published on December 20th, 2017
Hi there and thank you for using PetCoach to address your concerns. Based on your description and pictures, I would recommend having the red bump examined by a veterinarian so that the most appropriate diagnostic and treatment recommendations can be made. Your vet can insert a small needle into the mass to help better determine what the mass could be. The licking of the paws is likely due to an allergy and I would recommend reading the following article to see if this helps. Please let me know if you have any other questions or concerns and I would be more than happy to help you further.

https://www.petcoach.co/canigive/dog/benadryl/
1Pet Parents found this answer helpful

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