Recent Progress in Hair Science and Trichology

Abstract

IntroductionHuman scalp hair has a lot of important functions. Seasonal variations in hair growth and goosebumps caused by cold stimuli or emotions point to its evolutionary history 1,2) . The main function of hair is to protect our head and neck from sunlight (mainly UV rays) , thermal pain (extreme heat/cold) , and physical damage 3,4) . Hair is also essential as an excretory system for trace metals and acts as an accumulating tissue. Thus, the metal content in hair can reflect the body s condition for a long period, recording the history of personal exposure to metals 5−8) . Last but not least, hair style is deeply tied to gender 9−12) , religion, and culture, as we arrange our hair as we want to complete our entire look. It is said that the first barbering services were performed in ancient Egypt in 5000 B.C. with tools made from oyster shells or sharpened flint. In ancient Egyptian culture, barbers were highly respected individuals and surgeons were said to also serve as barbers. In addition to this, the earliest records on the usage of henna as a hair dye go back to ancient Egypt, where people used henna to decorate and color their hair and nails 13) . In Japan, people