My dog Ginny is a 9-week-old Chihuahua with a large knot on her back. She can walk just fine, but it hurts her when you touch it. I think it may move from one side to another. Do you know what it could be?
– Destiny, Tennessee
Any lump or bump on a dog should be closely examined by a veterinarian to make sure it is not a problem.
The most common reason for a lump on a dog this young is a vaccination lump. These are often seen following routine vaccinations in dogs and are from the vaccination itself, which creates a localized inflammatory response as it helps the body’s immune system recognize and develop antibodies against the virus. This localized inflammatory response can sometimes cause a palpable nodule in the area where the vaccination was administered. As the inflammation resolves, the lump will slowly disappear, although sometimes it can persist for several weeks.
Other possible causes for lumps on young dogs include bug bites or bee stings, trauma or bruising from playing too rough, developmental abnormalities, migrating parasites (called Cuterebra), and abnormal growths (which are more commonly seen in older dogs).