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Pet Rats/Lumps on mice


I know you are a rat expert, but I'm hoping you could help me with my mouse. I'm not sure on his age but if i were to guess he's probably 6-8 months. But i got him a few days ago from the store and he looked perfect.. then over night a small bump formed.. I didn't think anything of it until it started growing. He refuses to let me touch it and it worries me because I would hate for it to be more than just an abcess... What is the difference between an abcess and a tumor?

Hi Cheyanne,

I apologize profusely for the delay. I had a rat emergency.

Actually I am a mouse expert who subs for rats when no one is there!

Let me start with tumors.

A tumor on a mouse will continue to grow. Unlike rat tumors, mouse tumors are usually malignant- the mouse has cancer and the tumor will come back, sometimes within a week. So there is little use in removing a mouse tumor. They grow large and heavy and the mouse looks funny, but you wait until the day it is unhappy, to put it  down. It does not care if it is ugly or awkward. You may have to renovate a little for it, such as enlarging doorways. One way to tell a tumor from a cyst or abscess is that it grows at a steady pace. It does not usually pop up overnight.

A cyst is a collection of greasy material which starts at a hair follicle. It may go away on its own. It is not dangerous. Under no circumstances should you try to express it  (squeeze it out) yourself, unless it opens up on its own and drains; then, be gentle and keep it clean. If it gets large a vet can completely remove it.

An abscess is a collection of infected pus, from various causes including sometimes an infected cyst. An abscess can be hot, and often hurts, though not always. Sounds like his, right? An abscess should not be allowed to stay, because the infection can enter the body and cause blood poisoning, which will kill the mouse. It is best to go to the vet to have the abscess lanced and drained, and to have systemic antibiotics for the mouse.

An abscess wants to drain, and you can help it come to the surface by applying heat for 10 minutes twice a day. If it opens by itself  it may smell simply atrocious. In that case you want to keep it clean with cotton swabs and saline, which you can get from a drugstore.

If a vet visit is difficult, you can try something primary and see if it helps. This is a very inexact method, but it is cheap and easy and often works. It involves an antibiotic formulated for fish! The following post, though for a respiratory infection, gives you exact instructions.

If that, along with the heat, doesn't shrink or empty it,  the mouse needs the vet. As I said, the mouse can get blood poisoning and die.

One way you can sometimes tell that a lump is not a tumor is that abscesses and cysts sometimes have a dark center, but not always. Tumors don't.

Best of luck to him :) I hope it is an abscess that can be resolved or resolves itself quickly.



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Natasha Millikan


Consider me a sub, when no one else is available. NOTE YOU MUST NOT HAVE ONLY ONE RAT. JOIN MY FACEBOOK GROUP (because there are smarter people than me there!!): ***** ***** Excellent sites: **** **** **** **** **** ****


I have had rats for 3-1/3 years and have researched them extensively. I am a mouse expert with 40 years' experience with mice. The two species are similar and yet also quite different.

My Facebook group is Rats (and Mice) are Awesome.

I have a Bachelor's and two Master's degrees in Linguistics

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My Facebook group, Rats are Awesome, serves at the moment 5300 members, and, considering all the huge rescues, probably averages 5 rats per member. That means my clients are about 25,000 rats!!!

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