Pain in the left armpit when lifting heavy objects may be caused by muscle injury, shoulder dislocation, neuritis and axillary lymphadenitis. 1. When carrying heavy loads, the biceps muscle or chest wall muscle is strained due to overwork or improper operation, and the heavy loads hit the chest wall muscle, which will cause pain in the armpit. It may also cause the shoulder joint to dislocate forward and downward, resulting in shoulder ligament injury and axillary pain. 2. Often carry heavy objects so that the local skin in the armpit by friction, ulceration, infection with herpes zoster virus can cause intercostal neuritis, if the neuritis attack, there is a localized discharge-like or cut-like pain. Infection of bacteria can cause inflammation of the axillary lymph nodes, pain, in addition to local redness, swelling, heat and other inflammatory manifestations. Lifting heavy objects on the left side of the armpit pain is recommended to actively seek medical attention, physician guidance under the diagnosis and treatment.