Perspectives and Challenges of Hair Analysis

The document provides an extensive examination of human hair, detailing its anatomy, biology, and the factors affecting its growth and characteristics. It classifies hair into eight types based on physical attributes and discusses the composition of hair, primarily proteins and keratin, which contribute to its mechanical properties. The structure of the hair shaft, including the cuticle, cortex, and medulla, and the hair follicle, with its various compartments, are described in relation to hair elasticity and strength. The document also explores the role of melanin in hair color and the cyclical changes of the hair follicle's lower part, particularly the bulb and dermal papilla, which are essential for hair production and the anagen phase. Additionally, the document covers the hair follicle's development, growth phases, and the factors influencing hair cycling and melanogenesis, including the transition through anagen, catagen, telogen, exogen, and kenogen phases. It concludes by highlighting the complexity of hair as an organ and the necessity of considering these complexities when interpreting xenobiotic concentrations in hair.