The cyclical phases of growth (anagen), regression (catagen), quiescence (telogen), and shedding (exogen) in the life of a hair; one of the collection or mass of filaments growing from the skin of an animal, and forming a covering for a part of the head or for any part or the whole of the body. [ GOC:go_curators http://www.ncbi.nlm.nih.gov/pubmed/12230507 ]