The blood vessels are obviously blue, this is because the blood vessels are very close to the skin. This blood vessel is a vein, it should be in the subcutaneous tissue fat layer, if the fat is relatively small and thin, then the blood vessel will be very close to the skin, then you can see the blood vessel under the skin through the skin is blue. This is a normal phenomenon and not a disease. Because there is no fat protection, so this kind of blood vessels are easy to be traumatized or varicose veins appear, so you need to observe the changes of blood vessels, if the blood vessels continue to protrude from the skin, you need to avoid standing and sitting for a long time, it is better to wear varicose veins elastic stockings to fight the blood vessels to protect them.