Painful arterial blood draws may be caused by the failure to compress the arterial puncture site promptly and reliably after the draw, or by the thicker puncture needle, and the blood gushing out from the arterial puncture site area can cause very large amounts of subcutaneous bruising and irritate the skin causing pain, which is more common. The pressure of the arterial blood is very high, and the instantaneous influx of blood from the artery to the subcutaneous tissue can form a large amount of subcutaneous bruising, or even a pseudoaneurysm. At this point, the stimulation of the skin is greater, so the arterial blood draw is more painful than the venous blood draw.