The hair follicle is a multicellular structure, where each epithelial compartment is characterized by the expression of specific differentiation marker, and it can undergo dramatic tissue remodeling as a result of physiological or a pharmacological stimuli. In human hair follicles, the dynamics and tissue remodeling that occur during anagen-catagen transition and catagen progression were very elegantly described by Como and Bernard [82]. Using
monoclonal antibodies directed against keratin 14 expressed in the outer root sheath, trichohyalin, transglutaminase I and desmoglein expressed in the inner root sheath, and Ki67 antigen as expression of cellular proliferation, the authors characterized the movement and changes in each of the main hair follicle compartments during the catagen process. The effect of laser on the development of catagen in hair follicles can be studies using these marker proteins.