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My dog has a new, growing blister-like mole on her back. What is it?

Updated on September 23rd, 2025

Pet's info: Dog | Mixed Breed | Female | spayed | 1 year and 1 month old | 6 lbs

I have a 6 lb rat/chi mix that just developed a blister type mole on her back in the last week. It seems to have gotten bigger in the last couple of days. What is this?

3 Answers

Most Helpful Answer

Answered By Dr. Elizabeth

Veterinarian

Published on January 25th, 2019

I’m not sure if there was supposed to be a photograph attached to your post, but that would be helpful. Red raised masses can be something like infection or an ingrown hair. They can also be more indicative of a skin tumor. Of the skin tumors, most are benign but there is one called a mast cell tumor which is cancerous and needs to be removed quickly. When in doubt, I always recommend to have any type of skin mass examined by the veterinarian. Sometimes they can tell what it is based on exam. But just like with humans, not all skin tumors can be identified just by looking. The doctor may need to aspirate some of the cells to look under the microscope. That is the only way to accurately know what kind of tumor it is. I always recommend to play it safe with something like this! I hope this is helpful and please feel free to post any additional questions.

1Pet Parents found this answer helpful

Related Answers from Veterinarians

Answered By Dr. Elizabeth
Veterinarian
Published on April 23rd, 2019
From the photo, that looks almost like a mass. I recommend to have it examined by the veterinarian as red, hairless masses are concerning for a skin cancer called a Mast Cell Tumor. The doctor will palpate the lesion and will likely recommend to aspirate the cells if they suspect a mass.
Gambit should also wear an elizabethan collar to prevent him from licking the area as this can make it worse. It’s best to play it safe and have it checked out. I hope this helps and please feel free to post any additional questions.
1Pet Parents found this answer helpful
Answered By Ana M, DVM
Veterinarian
Published on September 26th, 2018
Thank you for submitting your question regarding Nacho. From your picture the skin mass appears to be red in color. If this is the case, I do recommend that he sees his veterinarian. A procedure known as a fine needle aspirate will likely be performed. The veterinarian will use a small needle to collect a sample of cells to evaluate under the microscope. This will help to diagnose the type of mass. There is a benign growth that is common in young dogs known as a histiocytoma. However, there is an aggressive type of skin cancer that has the same outward appearance. This is a called a mast cell tumor. The procedure is necessary to differentiate between the two and decide if treatment is necessary. I hope this information helps!
1Pet Parents found this answer helpful

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My dog has a red skin tag-like bump. Is it serious or benign?

That mass could be several things. Red raised hairless masses can be benign growths such as warts, histiocytomas, reactions or infected hair follicles. They can unfortunately also be malignant grows such as Mast Cell Tumor or Plasmacytoma. I would recommend to have it checked out by the vet who may be better able to tell how concerned you should be by palpating the mass and the surrounding lymphnodes. The good news is that the majority of masses are benign but it's always better to be safe. Thank you for using Petco Pet Education Center, formerly Petcoach!

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Hi, thanks for using Petco Pet Education Center, formerly Petcoach! Thanks for the pictures! Many skin masses can look the same. Red dermal masses, like this one, can be benign or malignant. Some possibilities are an inflamed sebaceous adenoma, hemangioma, histiocytoma or it could be a Mast Cell Tumor. Since it showed up quickly I would have Oscar seen by your Vet. They can decide if aspirating it (sticking it with a needle and sending the slides to the lab) or removing the mass and sending it for biopsy is best. I hope this helps and I wish you and Oscar the best!

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