Sclerotherapy is the most common treatment for both spider and varicose veins. This procedure involves a saline or chemical solution that is injected into the varicose veins that causes them to harden so that they no longer fill with blood. Blood that would normally return to the heart through these veins returns to the heart by way of other veins. The veins that received the injection will eventually shrivel and disappear. The scar tissue is absorbed by the body.