Spider veins are tiny, thin veins that vary in color and that you can see just under the surface of your skin. Mild spider veins in legs are a symptom of varicose vein disease. Aside from an unpleasant  appearance, they can also cause a variety of symptoms such as itching,  burning, heaviness, and cramping. 
Here, are guide to recognize the signs and symptoms of spider veins. Spider veins in upper thigh, leg, hand, and face are caused by unhealthy valves inside feeder veins, allowing blood to flow backwards instead of upwards toward the heart.  Some of our patients seek treatment for cosmetic improvement, and others are looking for relief from spider vein pain.

https://www.usaveinclinics.com/vein-disease-symptoms/spider-veins-telangiectasias/