In the hands of experienced medical professional, the discomfort of a vein treatment injection sclerotherapy should be minimal. An occasional spot may be more sensitive than others, but generally, the procedure should be well tolerated for most patients. Even the needle-phobic ones. In fact, most patients are pleasantly surprised at how little discomfort occurs during the procedure. Of course, pain perception is somewhat subjective, but several factors may affect the level of discomfort during injections. In addition, veins that usually ache before sclerotherapy tend to be generally more sensitive to injections than the ones that do not.