Musculoskeletal strain or injury: This is often the most common cause of arm pain, especially if the pain is acute and follows a specific incident or activity. The non-dominant hand is less likely to be involved in repetitive strain injuries compared to the dominant hand, but it can still be affected by direct trauma, overuse, or poor posture.

Cervical radiculopathy: Pain in the arm can be referred from the cervical spine, especially if there is nerve root compression. This condition can cause pain, numbness, and weakness in the arm and is a common cause of arm pain.
Thoracic outlet syndrome: Compression of the nerves and/or blood vessels that pass through the thoracic outlet (the space between your collarbone and first rib) can cause pain in the arm, especially with certain movements or positions.
Tendinitis or bursitis: Inflammation of the tendons or bursae around the joints of the arm can cause localized pain and stiffness, often related to specific activities or movements.

Acute coronary syndrome: Although less common, arm pain can be a symptom of a heart attack, especially if the pain is severe, radiates to other areas (like the jaw or back), and is accompanied by other symptoms like shortness of breath or nausea.
Peripheral artery disease: Severe blockage of the arteries supplying the arm can cause pain, especially with exercise, and is a critical condition to identify due to its implications for limb and overall health.
Brachial plexus injury: Trauma to the brachial plexus, the network of nerves that conducts signals from the spinal cord to the shoulder, arm, and hand, can cause severe pain, numbness, and weakness in the arm.

Complex regional pain syndrome (CRPS): A chronic pain condition characterized by severe, burning pain in the arm, often following an injury or trauma. It's rare but important to consider due to its significant impact on quality of life.
Pancoast tumor: A type of lung cancer located at the top of the lung that can cause arm pain by invading the brachial plexus or ribs. It's a rare condition but one that requires early detection and treatment.
Vasculitis: Inflammation of the blood vessels can cause arm pain, among other symptoms, and is a rare but potentially serious condition that may require immunosuppressive treatment.