The reason for the exposure of bruises on the arms may be caused by high physical fitness, thinness, gravity, and poor blood reflux. The exposure of veins is generally a normal physiological phenomenon, if the symptoms are caused by pathological diseases need to go to the hospital as soon as possible for diagnosis and treatment. 1. Physical fitness: Generally speaking, people with good physical fitness, such as soldiers, athletes, heavy manual laborers, etc., because of long-term high-intensity training or labor, the muscles of the whole body are very developed, the blood circulation is rich, blood vessels are angry, you will see the phenomenon of arm veins. 2. Slim body shape: Slim body shape, fair skin people, their body fat content will be less, when the force will see the obvious expansion of superficial veins, so you will see the phenomenon of veins exposed. 3. Influenced by gravity: When the arms are drooping, the blood flow will slow down, which will cause the expansion of superficial veins and the appearance of veins. 4. Poor blood return: because of the contraction of venous valves or thrombosis in the veins of the upper limbs, the superficial veins become tortuous and dilated, resulting in the appearance of veins. In addition, when the blood pressure is too high, the pressure of blood vessels increases, peripheral veins dilate, and bruises may also appear. If discomfort occurs, please seek medical attention.