A complication of sclerotherapy regardless of the sclerosant used is pigmentation over or around the treated blood vessel. Pigmentation is caused by haemosiderin staining of the dermis. The haemosiderin probably comes from red blood cells that extravasate into the dermis as a result of the inflammatory response or ruptured vessels.

The level of pigmentation seems to be dependent on the level of inflammation. Lower concentrations of Fibro-Vein are effective at sclerosing small veins but cause less inflammation and consequently less pigmentation. It has been shown that use of lower concentrations of STS reduces the level of pigmentation (Tretbar 1989).

Other factors that can influence the level of pigmentation include gravitational pressure. Lower levels of pigmentation are seen if the treatment proceeds in a proximal to distal manner. Injecting the thread veins first can result in more pigmentation due to pressure from the feeder vein causing RBC’s and haemosiderin to extravasate. Applying compression will also help.