A lump under the armpit, painful when pressed, may be a local lesion of the tissue under the armpit, which may be a breast disease, lymph node lesion or skin lesion. It is recommended that the patient seek medical attention in a timely manner to be clarified by the doctor and then deal with it accordingly. I. Breast diseases: 1. Breast hyperplasia: The breast tissue under the armpit can be called parametrium, which also has a mammary gland and can appear as a breast disease. If the patient has a lump under the armpit, which is painful when pressed, it may be a mammary hyperplasia of the parametrium, which can be treated conservatively first under the guidance of a doctor, with commonly used drugs such as breast numbing tablets and tamoxifen. If conservative treatment is ineffective, patients can choose surgery according to their personal situation; 2. Breast fibroadenoma: a common benign tumor of the breast, related to estrogen abnormalities. A lump may appear in the subaxillary parametrium, and if accompanied by inflammation, it may be painful when pressed. Currently, most of them are treated by surgical excision and can be treated with medication. 3. Breast cancer: Parammary glands only have glands without milk ducts or nipples, which may lead to secretions that cannot be discharged, thus inducing breast cancer. It can be manifested as a lump under the armpit and can be painful when pressed. It is usually treated by radical excision, together with radiotherapy, chemotherapy or endocrine therapy. Lymph node lesion: There are lymph nodes under the human armpit. When the lymph nodes become inflamed or hyperplastic, local lumps will appear, which may be accompanied by painful symptoms when contacted, usually related to fungal or bacterial infection in the adjacent tissues, causing lymph node inflammation. Clinically, antibiotic treatment, such as amoxicillin and cefuroxime, is often used. External application of Chinese herbal medicine and infrared therapy can also be used to relieve the condition according to the patient. Third, the skin lesion: 1, sebaceous cyst: if the patient under the armpit skin appear sebaceous gland stasis, may form sebaceous cyst, that is, manifested as a lump, pain when pressed, the central part of the lump will have a black spot or black head, pressure can appear similar to tofu slag-like material, secondary infection manifested as the lump increased, the surface is red, accompanied by pain, can choose the surgical removal of the way to achieve radical treatment, if accompanied by infection should choose suitable 2, lipoma: lipoma is a common clinical dermatological disease, patients with painful lumps under the armpit, may be the growth of lipoma to a certain extent, the local tissue compression caused by the lipoma, usually surgery can be removed, not easy to recur.