My 20 year old daughter developed a very large growth under her armpit at age15 or 16. She saw a general practitioner and a dermatologist who both said it was probably not anything to worry about. They suggested using an antipersperant rathar than deoderant thinking it might be clogged pores. The gland or growth seems to enlarge and reduce with her menstrual cycle but it is getting larger with time. Now she is feeling a small nodule under the other arm and a new additional one under the first arm. They are tender and swollen.