<s>[INST] Hi I m a 19 year old boy and there is a lump under my right nipple and it is very tender to the touch. It s aldo started to swell since I ve been messing with it. What is it? Should I be worried. This happened once when I was 15 and it went away and it wasejt as painful. [/INST] Hi. Thanks for your query and an elucidated history. Your age of 19 and twice the appearance of the painful lump under right nipple indicate that you may have one of the following problems:-This can be due a sebaceous cyst and you're fiddling with it caused it to grow and cause pain. -Gynecomastia is another possibility. I would advise you the following:Get examined by the General Surgeon and get this removed for 2 reasons:1. You get rid of the problem.2 you get a certain diagnosis. </s>