Hair growth

How to set up a scientific study to assess cosmetic aspects of hair? This is an ever difficult to answer question, since hair cosmetic means hair appearance which is a result of many parameters such as the single hair shaft form, strength, flexibility, hardness and smoothness which in sum of all quality parameters and sum of all hairs on the scalp lead to that positive appearance that is called beautiful hair. The line between cosmetic and medical hair aspects is blurred, and in most cases, however, studies are mostly performed not to improve the quality of single hair parameters, but to prevent hair loss and to increase hair density and volume. Therefore, most hair assessment parameters measure hair growth and density and assess different hair types (anagen-, telogen-, vellus-, terminal-hair).