Hard lumps in the arm that hurt when pressed may be caused by lipoma, sebaceous cyst or fibroma, etc. They can be treated by surgery or other means depending on the situation. 1. Lipoma: It is composed of mature fat cells, and can occur in any part of the body with fat. Lipoma on the arm will appear as a localized lump with nerve compression symptoms and pain when pressed. If the symptoms are obvious and the lipoma is large, it can be treated by surgery, making proper surgical incision on the surface of the lipoma and removing the lipoma completely free. 2. Sebaceous cyst: it may be caused by the infection of sebaceous glands in the arm, and sebaceous cysts will be painful to press when it is inflamed. At this time, you can use anti-inflammatory analgesic cream to help control the inflammation, if recurrent episodes can be surgically excised, along the dermatoglyphic direction to make an incision, the cyst and the skin to separate and remove. 3. Fibroma: It is mainly caused by the abnormal growth of fibrous connective tissue. Painful symptoms can occur, which can be manifested as a lump in the arm and pain when pressed. It can be treated by surgery. After successful anesthesia under local anesthesia, a straight incision is made at the fibroid site, and the skin and subcutaneous tissues are cut, and the fibroid can be peeled off as a whole. If the above symptoms occur, it is recommended to go to the hospital in time for early and regular treatment.