title: Paradoxical hypertrichosis after laser therapy: a review.
abstract: BACKGROUND
  Laser hair removal is a safe and effective procedure for the treatment of unwanted body hair but is not exempt from side effects. A rare but significant adverse effect with this treatment modality is paradoxical hypertrichosis.
  
  
  OBJECTIVE
  To evaluate the potential etiologies, risk factors, related laser types, and treatment options for the development of excess hair after laser therapy.
  
  
  METHODS
  An analysis of previously published case studies and review articles along with our own experience was used to gather information regarding this phenomenon.
  
  
  RESULTS
  Paradoxical hypertrichosis has a low incidence, ranging from 0.6% to 10%, and most commonly occurs on the face and neck. All laser and light sources have the potential to cause hair induction, especially in individuals with darker skin types (III-VI); with dark, thick hair; and with underlying hormonal conditions. Possible causes include the effect of inflammatory mediators and subtherapeutic thermal injury causing induction of the hair cycle. Treatment for paradoxical hypertrichosis is laser therapy of the affected area.
  
  
  CONCLUSIONS
  Paradoxical hypertrichosis is a rare side effect of laser hair removal; the pathogenesis of this event remains widely unknown. We recommend further large-scale studies to investigate this effect. The authors have indicated no significant interest with commercial supporters.
authors.affiliation: Department of Dermatology, Loyola University, Maywood, Illinois 60563, USA. shraddha.desai@dupagemd.com
authors.forename: Shraddha
authors.initials: S
authors.lastname: Desai
authors.forename: Bassel H
authors.initials: BH
authors.lastname: Mahmoud
authors.forename: Ashish C
authors.initials: AC
authors.lastname: Bhatia
authors.forename: Iltefat H
authors.initials: IH
authors.lastname: Hamzavi
mesh_terms: D018859:Hair Follicle / Q000293:injuries / Q000503:physiopathology; D006204:Hair Removal / Q000009:adverse effects* / Q000379:methods; D006801:Humans; D006983:Hypertrichosis / Q000453:epidemiology / Q000209:etiology* / Q000503:physiopathology; D053685:Laser Therapy / Q000009:adverse effects*; D012307:Risk Factors