Hello,
This lump can be a small cyst, hematoma, mucocele (if present on the inside of
lower lip) or a benign growth of the lips. Since the
lump is painless and not changing
in size, all these possibilities need to be evaluated.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your dermatologist. I sincerely hope that helps.