Breast enlargement does not normally cause arm aches and pains, but the pain of breast enlargement can be severe enough to involve the upper limbs and appear as a self-perceived soreness in the upper arms. However, arm pain can also be caused by muscle strain, tendonitis and other reasons. 1. Mammary gland hyperplasia: Since some nerves in the mammary gland are connected to the shoulder and arm, when the glandular hyperplasia in these areas is obvious, it will radiate to the shoulder or arm, causing arm pain. 2. Muscle strain: arm muscles are in a state of contraction for a long time, so that the muscle fatigue lactic acid accumulation as well as muscle fiber congestion and edema, thus causing arm pain. 3. Tendonitis: due to excessive strain, strenuous exercise or cold stimulation of the patient’s tendons localized inflammatory reaction, triggering significant pain, soreness, and limited activity performance, often occurring in the excessive amount of exercise or prolonged exercise people. There are many causes of arm pain, it is recommended that patients with arm pain should go to a regular hospital in a timely manner, to clarify the cause of the disease, under the guidance of a professional doctor to take targeted treatment.