What could cause a bump under the skin at the base of a dog's tail?

Answer:
This could be a cycst, burn, wart, ingrowing hair, scar tissue, or a cancerous or noncancerous tumur among other things. If you have only noticed it recently then it is not a reason to panic, but it would be wise to have it checked soon by a vet.
First answer by Joebron. Last edit by Joebron. Contributor trust: 4 [recommend contributor recommended]. Question popularity: 1 [recommend question].