What could be a painless ulcer in mouth?

It depends. This depends on your age and habits. If you are older and have a history of tobacco (including snokeless) and alcohol use, you should see your doctor for work-up of a possible oral cancer. If you are younger, it might be infectious. At any rate, you should go to your doctor for work-up and treatment.

Related Questions

I'm having anal wart outbreak, then a fever and running nose like flu. I have 1 painless ulcer at roof of mouth. Is it herpes? I also had hot chilli.

Be sure of diagnosis. Get examined please. Canker sores are common aphthous ulcers of mouth that occur situationally, often in response to stressors, are bacterial or viral, can be treated topically with many otc products that reduce local discomfort &potentially speed healing. However, oral/dental problems & a number of systemic diseases cause canker sore-like lesions--Crohn's, Behcet's, STD (sexually transmitted). Read more...