Spider veins are small, damaged veins that can appear on the surface of the legs. They are usually not painful or harmful, but some people may wish to treat them for cosmetic reasons. Spider veins can be blue, purple, or red and may appear in the form of thin lines, webs, or branches. People sometimes also refer to them as thread veins. A range of treatments can remove spider veins or reduce their appearance.

In the legs, spider veins can occur when the valves inside the veins stop working properly. Veins carry blood back to the heart. To prevent blood from flowing backward, they contain a one-way valve that closes once the blood passes through it. If this valve weakens or becomes damaged, the blood may struggle to flow in the correct direction, and it can begin to pool inside the vein. Over time, this can cause a bulge in the vein that branches out, resulting in spider veins.

Spider veins on the face are often the result of tiny blood vessels bursting. Increased pressure or sun damage can cause this to occur. Spider veins and varicose veins are different forms of a medical condition called venous insufficiency. In the legs, both conditions result from having weakened or damaged valves in the veins. However, the two issues have different symptoms.

Spider veins are usually small, thin lines that may be flat or only slightly raised. They are often blue, red, or purple. Although they can cause some discomfort, they are painless most of the time. Varicose veins are larger and deeper than spider veins. They may also appear lumpy or twisted and are usually flesh-colored or red.