title: Influence of the anagen:telogen ratio on Q-switched Nd:YAG laser hair removal efficacy.
abstract: OBJECTIVE
  Laser hair removal is believed to affect only anagen hairs. However, proof of this belief in humans is lacking. The objective of this study was to determine the influence of the anagen: telogen ratio on the results of Q-switched Nd:YAG laser hair removal.
  
  
  METHODS
  Fifteen subjects had four test sites delineated in one body area. The test sites were chosen by trimming the hair and evaluating the area in 2 weeks. At that time, the anagen hairs were at least twice as long as the nongrowing telogen hairs and, therefore, could be differentiated and counted. Two sites with a low anagen number and two with a high number were chosen for comparison. All sites were then treated with a Q-switched Nd:YAG laser. Follow-up examination was in 1 month.
  
  
  RESULTS
  Test sites with a low anagen number demonstrated a low level of hair loss compared with those sites with a high anagen number. A significantly higher percentage of hair loss was noted when comparing the anagen-only with total hair loss. In addition, lasing plus shaving demonstrated more hair loss than lasing alone. These findings indicated that anagen hairs were clearly affected, but the immediate clinical effect on telogen hairs was minimal.
  
  
  CONCLUSIONS
  Q-switched Nd:YAG laser treatment of anagen hairs results in a rapid switch to telogen and a subsequent clinically obvious shedding of the hair shaft. This process causes a greater percentage hair loss at sites with high anagen number. Telogen hairs demonstrate no such effect and remain in their pretreatment phase after lasing.
authors.affiliation: ThermoLase Corporation, San Diego, California 92121, USA.
authors.forename: V G
authors.initials: VG
authors.lastname: Kolinko
authors.forename: C M
authors.initials: CM
authors.lastname: Littler
authors.forename: A
authors.initials: A
authors.lastname: Cole
mesh_terms: D000328:Adult; D006197:Hair / Q000254:growth & development*; D006204:Hair Removal / Q000379:methods*; D006801:Humans; D007834:Lasers; D013997:Time Factors