With sclerotherapy, a chemical solution is injected into the vein to irritate its lining, causing it to swell, collapse and turn into scar tissue, which the body absorbs. Spider veins and large blue varicose veins on legs. It takes about 15 to 30 minutes. After several treatments, you will see a 50 to 90 percent improvement. But fading takes a few months. Results last about one year. If varicose veins have been treated, vigorous exercise is discouraged for 24 hours, and you may need to wear support hose for two days to three weeks.