Higher blood pressure in the left arm than in the right arm may be a normal physiological phenomenon, or it may be caused by the obstruction of the right subclavian artery and other lesions. 1. Normal physiological phenomenon: generally healthy people’s left and right upper arm blood pressure is indeed different, usually the difference between the two sides of the blood pressure ≤ 20mmHg. This is due to the normal conditions, the left arm and the right arm to carry out activities with different intensity and utilization, so the thickness of the arteries and the strength of the muscle is different, which will lead to the difference in blood pressure. This situation does not cause harm to the human body, belongs to the physiological difference in blood pressure. In addition, the left arm of the blood pressure is higher than the right arm, there may be a measurement error, you can eliminate the error through multiple measurements. 2. Pathological factors: If the right subclavian artery and its distal end have obstructive lesions, arteritis and other problems, it will lead to a decrease in blood flow in the right brachial artery and a decrease in pressure on the blood vessel, resulting in a higher blood pressure in the left arm than in the right arm. This condition can be detected by arterial ultrasound to find out the cause of the lesion. Therefore, if you find that your blood pressure is higher in the left arm than in the right arm and this is true after several measurements, it is recommended that you seek medical attention and follow the doctor’s instructions for examination and treatment in order to avoid any delays in your condition.