Does oral cancer only develop outside of the lip or on the inside of the lip?

NO: Oral cancer can ocurr anywhere in the oral cavity, in the lip, gums, tounge, etcc. It can ocurr on the outsied of the lip (the part we see) or the inside of the lip.

Both.: If you have a nonhealing ulcer that can be painful, have it checked out. This disease usually is seen over age 50, but alcohol and tobacco use (also smokeless) are risk factors, so some people might get it earlier.

Both: Cancer of the lip can be on the inside or outside. Oral cancer can also affect other structures, e.g., tongue, cheek, tonsils, pharynx etc.