The common causes of discomfort in the right armpit and back are muscle strain, soft tissue strain, intercostal neuralgia, lymphadenitis, etc. The most common causes of discomfort in the right armpit and back are muscle strain, soft tissue strain, intercostal neuralgia and lymphadenitis. 1. Muscle strain: If you are engaged in heavy physical work for a long time and use your shoulders and back to carry heavy loads, it is easy to cause chronic strain of the back muscles, and if you are stimulated by cold, it may cause uncomfortable feelings in the right armpit and back. 2. Soft tissue strain: If you play strenuous sports or keep wrong posture, it is easy to cause back muscle sprain, which will cause the symptom. 3. Intercostal neuralgia: secondary intercostal neuralgia is mostly related to diseases and trauma, the main clinical manifestations include pain around the ribs and the back, the nature of the pain is mostly stinging or burning pain, and the pain symptoms can be aggravated when sneezing. 4. Lymphadenitis: mostly caused by bacterial infection, prone to underarm and adjacent back pain, usually accompanied by lymph node enlargement. The causes of discomfort in the right armpit and back are many, and may also be related to fasciitis, breast disease, etc. If the symptoms do not improve after rest, it is recommended to go to the hospital in time to find out the cause of the disease, and carry out targeted treatment.