title: The optimal patch test concentration for ascaridole as a sensitizing component of tea tree oil.
abstract: BACKGROUND
  Tea tree oil is used as a natural remedy, but is also a popular ingredient in household and cosmetic products. Oxidation of tea tree oil results in degradation products, such as ascaridole, which may cause allergic contact dermatitis.
  
  
  OBJECTIVE
  To identify the optimal patch test concentration for ascaridole, and to investigate the relationship between a positive reaction to ascaridole and a positive reaction to oxidized tea tree oil.
  
  
  METHODS
  Three hundred and nineteen patients with eczema were patch tested with ascaridole 1%, 2%, and 5%, and 250 patients were patch tested with oxidized tea tree oil 5%. Readings were performed on D3 and D7 according to a patch test calibration protocol.
  
  
  RESULTS
  With an increasing ascaridole test concentration, the frequency of positive reactions increased: ascaridole 1%, 1.4%; ascaridole 2%, 5.5%; and ascaridole 5%, 7.2%. However, the frequencies of irritant and doubtful reactions also increased, especially for ascaridole 5%. A positive reaction to ascaridole was related to a positive reaction to tea tree oil.
  
  
  CONCLUSIONS
  This study is in support of ascaridole being a sensitizer. We recommend patch testing with ascaridole at 2%. The finding that every positive reaction to oxidized tea tree oil is accompanied by a positive reaction to ascaridole suggests that ascaridole might be a contact allergen in oxidized tea tree oil.
authors.affiliation: Department of Dermatology, University Medical Center Groningen, University of Groningen 9700RB, Groningen, The Netherlands.
authors.forename: Wietske Andrea
authors.initials: WA
authors.lastname: Christoffers
authors.forename: Brunhilde
authors.initials: B
authors.lastname: Blömeke
authors.forename: Pieter-Jan
authors.initials: PJ
authors.lastname: Coenraads
authors.forename: Marie-Louise Anna
authors.initials: ML
authors.lastname: Schuttelaar
mesh_terms: D000328:Adult; D000368:Aged; D000081005:Cyclohexane Monoterpenes; D017449:Dermatitis, Allergic Contact / Q000175:diagnosis*; D005260:Female; D006795:Household Products / Q000009:adverse effects; D006801:Humans; D008297:Male; D008875:Middle Aged; D039821:Monoterpenes / Q000008:administration & dosage*; D010328:Patch Tests / Q000379:methods*; D010545:Peroxides / Q000008:administration & dosage*; D020947:Tea Tree Oil / Q000008:administration & dosage*; D055815:Young Adult
chemical_list: D000081005:Cyclohexane Monoterpenes; D039821:Monoterpenes; D010545:Peroxides; C043372:ascaridole; D020947:Tea Tree Oil
keywords: Melaleuca alternifolia; allergic contact dermatitis; ascaridole; tea tree oil