The arm has hard lumps, more consider 4 points of reason.1, fibroma, for the most common subcutaneous benign tumors, there are fibroblasts heterogeneous hyperplasia formation, local aggregation of fibroblasts, clear boundaries, the texture is tough, ping-pong ball-like, can be pushed.2, lipoma, due to the formation of subcutaneous adipocytes heterogeneous hyperplasia aggregation, softer, clear boundaries, more than one can exist, no pressure pain. If there is obvious pressure and pain and the border is not clear, surgical excision is required.3, epidermoid cysts, due to local trauma, intramuscular injection of the skin embedded in the subcutaneous, local hyperplasia cysts, if the cysts are infected, redness, swelling, heat and pain often occurs, surgical excision is required.4, sebaceous cysts, for the hair follicle sebaceous retention of cysts, combined with the infection of the pus has a foul odor, need to be cut and drain the operation.