What is a hair system?
A hair system is defined by the American Hairloss Council as "Any external hair bearing device added to existing hair or scalp to give one the appearance of a fuller head of hair. (i.e. Hair weaves, hair extensions, hair pieces, toupees, non-surgical hair replacements, partial hair prostheses, hair wefts, etc.) Devices may consist of human hair, synthetic fiber or a combination of both." These hairs are generally dyed to match your own hair. There are many variations of systems which can make a difference in how good it looks and how detectable it is. There are also different ways of attachment which will influence how much you like having it on.
