Immediately post-treatment, you may see multiple red, raised bumps all over the treated areas. This is called the "red response" and is actually a desired outcome. The bumps will look (and itch) like a bug bite and resolve 20-30 minutes after treatment.
Please note, sclerotherapy "kills" unwanted veins, prompting the body to then absorb and eliminate them as waste. Appearance of the veins will worsen before they get better, as the body absorbs different-sized veins at different rates. During this process, veins will initially darken in appearance and there will be some degree of bruising from the injections, as well as some hyperpigmentation (as iron in the blood will remain on the surface of the skin as the body absorbs the actual vein membrane and components).