They are micro dilatations of blood vessels caused by an abnormality in the normal flow of blood. This causes it to spin, accumulate and show a more intense color under the skin. If it sounds strange to you, it is something similar to the causes of dark circles that are a dilation of the blood vessels around the eyes. If you notice, they match in the color that can go from pink to red and darken from purple to black. But spider veins are very common in the legs, ankles and in the nose. Although aesthetically for you are a problem, if you go to the doctor will tell you that they are not. He will call them telagiectasias and they are somewhat different from varicose veins. These can cause discomfort, pain and health problems.