Sclerotherapy is the most common treatment for both spider and varicose veins and many times will follow an endovenous ablation procedure or surgery. It is wrong to start with sclerotherapy of spider veins before checking for underlying venous insufficiency that should be treated first. Many spider and some varicose veins will disappear if the deeper and larger veins, that are feeders of the spider veins, are removed. The residual ones can be taken care with sclerotherapy.
Sclerotherapy involves injection with a tiny needle of a liquid chemical solution into the spider veins that causes them to harden so that they no longer fill with blood. The veins that received the injection will eventually shrivel and disappear. The scar tissue is absorbed by the body. For larger varicose veins the chemical solution can be more effective if used as foam (instead of liquid). The procedure is called foam sclerotherapy and it can be done in deeper veins requiring ultrasound guidance.
Both "straight" and foam sclerotherapy are essentially painless and the process takes 20-40 minutes depending of the size of the treated area. The leg will then be dressed in a stocking or multilayer compression dressing for 48 continuous hours and then daily for 2 weeks (no need to wear them during the night sleep). You will need to return to your vascular surgeon's office in 2 weeks for reassessment and to continue sclerotherapy as needed. In most cases, more than one treatment session will be required. You should also expect that sclerotherapy in really big bulging varicosities may result in redness and tenderness of the injected area that may need a few months to resolve. In such cases mini phlebectomies may be preferable.
Sclerotherapy as all medical interventions carries some risks, rare (less than 1%) but sometimes can be quite critical: skin discoloration and skin necrosis that will heal overtime, allergic reaction and deep venous thrombosis (extremely rare).