My 19 yr son has a marble sized hard lump under his chin that has been there for a year now and he has lost about 10 lbs. since this time last year. ?

Need to see MD: He needs to see his pmd and have further evaluation. He needs a careful history taking and examination- especially on the facial area, mouth as well as throat, blood works, perhaps an imaging study like a ct scan would be needed. In addition, a biopsy of the hard lump is likely will need to be done -but off course as indicated by the doctor after a careful examination. Good luck.

Agree with Dr. Ho: It is time to see a doctor. Weight loss is an issue to be concerned about.