title: [Seasonal variation of trichogram in Chilean subjects].
abstract: BACKGROUND
  Human hair follicle experiments cyclical transformations throughout its life. These are rest (telogen phase), growth (anagen phase) and regression mediated by apoptosis (catagen). During summer the percentage of telogen increases and the percentage of anagen decreases.
  
  
  OBJECTIVE
  To determine the seasonal changes of scalp hair follicle phases among Chilean subjects.
  
  
  METHODS
  Retrospective analysis of 514 differential trichograms of normal scalps from subjects aged 36+/-14 years, obtained between 1998 and 2008.
  
  
  RESULTS
  During summer and winter, the mean percentage of telogen was 20%+/-10% and 16%+/-10%, respectively (p <0.01). The figures for anagen in the same periods were 80%+/-10% and 83%+/-10%, respectively.
  
  
  CONCLUSIONS
  This study confirms the presence of seasonal variations in normal trichogram.
authors.affiliation: Servicio de Salud Metropolitano Norte, Santiago, Chile. marianakahnchernilo@hotmail.com
authors.forename: Mariana
authors.initials: M
authors.lastname: Kahn Ch
authors.forename: Robinson
authors.initials: R
authors.lastname: Guerrero A
authors.forename: María Cristina
authors.initials: MC
authors.lastname: Césped
mesh_terms: D000328:Adult; D002677:Chile; D005260:Female; D018859:Hair Follicle / Q000254:growth & development*; D006801:Humans; D008297:Male; D012189:Retrospective Studies; D012535:Scalp / Q000502:physiology*; D012621:Seasons