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This is the lump under is foot
This is the lump under  

the lump
the lump  
Hi, i dont know what to do or what to go to but i hav a male mouse and i recently noticed on his back foot under it, there is a giant lump like the size of a pea under his foot its black and purple in color im so scared please help me get some idea of what it is

Hi Sarah,

Several things can cause a swelling like this, but a vet is the only person who can tell you for sure what is causing it.  Some possibilities include hematoma (a collection of blood from an injury), edema (a collection of fluid), pododermatitis (an infection in the foot causing an abscess or swelling), or even an allergic reaction.

Since it is so dark in color, this makes me think it is likely a hematoma, but there is no way for me to tell you for sure.  A hematoma is pretty much like a bruise, but swollen because of the amount of blood that has collected in it that has nowhere to go.  Over time, hematomas will reabsorb into the body and you will see the lump go down in size.  The things to watch for, however, are if the lump grows larger, or if it starts to ooze, burst, or scab over, which can happen if it gets irritated as he tries to move around on the foot.  Another thing to consider is what caused it - usually these are the result of an injury.  Could he have caught his foot in something, or hurt it in some way in his cage?  Take a peek around his home and see if you can spot any hazards that you could remove for a while.  If he uses a wheel, it would be a good idea to remove it for now, since he won't be very inclined to use it with his foot hurting him and it could make it worse.

If you have a vet in your area who is familiar with pocket pets like mice, it would be a very good idea to give them a call if:
-Swelling increases
-You see discoloration in other parts of the foot
-The foot begins to leak or scab, or smell funny
-He stops using his leg
-The swelling goes down but he still does not use his foot, or it looks different from his other feet once the swelling is gone
-He becomes lethargic (slow moving and uninterested), stops eating or drinking, or acts different from his normal self in ANY way

These are all signs that something serious is going on or that the foot could be infected.  If you have the ability to go to a vet now that would be even better, as a professional would be able to be sure nothing else is going on and that it really is a hematoma, and not something more serious.  Vets know best!

Best of luck to him, and if you have any other questions or need any help just let me know!


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I can answer questions regarding mice as pets, mouse behavior, color and coat genetics, breeding techniques, and general health questions. I can help with caging and setup, nutrition, social issues, and what to do in most mouse emergencies (such as unplanned litters, injuries, fighting, etc.). I can also assist with questions pertaining to orphaned mouse pups, weaning litters, and questions of mating and birthing. I cannot answer questions about exotic or wild varieties of mice such as spiny or pygmy mice. *****FOR EMERGENCIES, anything requiring immediate medical intervention, PLEASE take your mouse to a professional veterinarian or wildlife rehabilitator who works with mice as soon as possible! IMPORTANT RESOURCES: Raising Orphaned Mice: Orphaned Mice Videos: Natasha's Your First Mouse: General Mouse Help: Mouse Info and Exotic Breeds:


I have enjoyed the companionship of mice nonstop since 2004, and spent a year caring for them in a lab where I learned a great deal about their breeding, social needs, and health. I spent a few years breeding them, specifically working with albinos, marked mice, angora mice, and satins. My education never stopped - I am learning something new every day from current and well-established research thanks to the wonderful folks at the Jackson Laboratory, as well as from my wonderful mousey friends online. I also love learning from my terrific questioners here on AllExperts - you folks keep my passion for these amazing animals alive and well!

East Coast Mouse Association - expired, American Fancy Rat and Mouse Association - expired

Partial University for a B.S. in Microbiology, Partial University for a 2-year degree in Veterinary Technology (RVT cert), C.E. classes in pathogens, aseptic technique, genetics, and applications

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