There is a bag on the upper side of the armpit of the right leg, which is considered to be related to lymph node enlargement, lymphadenitis, sebaceous cyst, popliteal cyst and other diseases, you can go to the hospital for examination to clarify the cause of the disease, and then timely medical treatment. 1. Enlarged lymph nodes: generally due to inflammation stimulation of lymph nodes, resulting in lymph node hyperplasia, the phenomenon of a bag on the upper side of the armpit of the right leg, swollen lymph nodes may also have pain, swelling and other symptoms. 2. Lymphadenitis: usually due to lymph node inflammation stimulation reactive hyperplasia, which in turn causes the phenomenon of a bag in the armpit of the right leg, lymphadenitis will usually appear red, swollen, pain and other symptoms. 3. Sebaceous cysts: may be due to excessive sebaceous gland secretion, gland duct blockage, caused by the phenomenon of a bag on the right armpit, sebaceous cysts usually appear swelling, pain and other symptoms. 4. Popliteal cyst: It may be primary popliteal cyst or secondary popliteal cyst caused by intra-articular disease, which increases the pressure in the joint cavity, and the fluid in the joint expands through the weak area behind the knee joint capsule, forming a cyst. If there is a bag on the upper side of the armpit of the right leg, in daily life, you should pay attention to rest, keep the local skin clean, and exercise appropriately. There may also be other reasons, it is recommended to go to the hospital in a timely manner, improve the examination to clarify the cause of the disease, give targeted treatment or treatment.