A broken blood vessel in the arm can be caused by an injury, bruise, allergic reaction, viral infection, blood illness or an autoimmune disorder, according to the New York Times. Aging skin and medical treatments such as chemotherapy or radiation can also cause broken blood vessels, as can some medications.
Certain medications, such as anticoagulants, aspirin, steroids or antiplatelet medications, can cause blood vessels to break within the arm, according to the New York Times. Diseases such as leukemia and idiopathic thrombocytopenic purpura often include broken blood vessels as a symptom.
A broken blood vessel is an alteration to the normal blood flow in an arm vein or artery, according to Healthgrades. As a result, underlying blood vessel conditions such as an aneurysm or atherosclerosis develop.
People with atherosclerosis develop the condition due to high blood cholesterol levels, smoking, a high-fat diet, high blood pressure, genetic risk factors or diabetes, according to Healthgrades. With this condition, plaque builds up in the arteries that carry blood to limbs, such as the arms, and red dots appear because of bleeding under the skin caused by a broken blood vessel. Blood may also collect under the tissue in large bruised areas of the arm and cause pain or discomfort for patients with this condition.