My hamster has a cheek lump that isn't food. What could it be?

You are right in thinking this is unusual for a mouse. It is possible for food to get caught in the space between the chewing teeth and the cheek. Sometimes this happens if the there is dental disease, particularly a malocclusion of the teeth. It is possible for the food pellet to be too dry and that is why it could be lodged/stuck there. Lastly, there could be tissue swelling, such as a dental abscess that is at this location and it is not food at all. If your mouse will let you safely look in the mouth using a q-tip or a popsicle stick, I would start there. You may need a flashlight to help you be able to see as well. If this causes Nutmeg to stop eating, traumatize the skin around the mouth and become lethargic, then I recommend having her examined by your veterinarian.

I can't really see properly as the pictures are very blurry but it is likely to be his cheek pouch that is protruding outside, you will have to take him to the vet ASAP, the pouch will need to either been sutured back inside or removed surgically.

If Hannibal has an abscess, this is actually painful and can make him quite sick. Hamsters are good at hiding illnesses and pain because they are prey animals, so he may be feeling pretty badly without seeing obvious signs. The best thing for him is to have him seen by a vet in the morning. An abscess has to be treated by a vet.

Stormz needs to see a veterinarian immediately. This appears to potentially be a problem with his cheek pouch and I'm concerned that it's turning black because the tissue is dead. Please have him seen quickly.

I would need to see it to confirm but it is probably a tumor, in hamsters these tumors are usually malignant and not treatable, surgery is a possibility but it would personally not recommend it. other than that there is very little that can be done, if the lump ulcerates then antibiotic treatment can be attempted to treat the secondary infection.

It has the appearance of an abscess or other infection. She likely needs antibiotics for treatment. These require an exam with your veterinarian before they can be dispensed. In the meantime, keep the area clean and dry. The most you can do is use diluted Betadine or chlorhexidine (Hibiclens) to cleanse the area daily. Monitor for lethargy or loss of appetite.

It may be an abscess or mass. A visit to your veterinarian would be recommended. A fine needle aspirate can be done in the clinic to collect samples for pathology. If it is an abscess, it may be drained and antibiotics dispensed. If it a mass, benign or malignant, you can discuss treatment options with your veterinarian.