If the sclerosant is injected properly into the vein, there is no damage to the surrounding skin, but if it is injected outside the vein, tissue necrosis and scarring can result. Skin necrosis, whilst rare, can be cosmetically "potentially devastating", and may take months to heal. It is very rare when small amounts of dilute (<0.25%) sodium tetradecyl sulfate (STS) is used, but has been seen when higher concentrations (3%) are used. Blanching of the skin often occurs when STS is injected into arterioles (small artery branches). Telangiectatic matting, or the development of tiny red vessels, is unpredictable and usually must be treated with repeat sclerotherapy or laser.