title: Determination of the minimal erythema dose for ultraviolet A1 radiation.
abstract: BACKGROUND
  There is limited knowledge of the potential of ultraviolet A1 (UVA1) radiation to induce erythema.
  
  
  OBJECTIVE
  To investigate the minimal erythema dose (MED) for UVA1 in a German and Austrian population and to determine UVA1 dose-response curves for erythema and pigmentation.
  
  
  METHODS
  We determined the UVA1-MED in 59 participants using a geometric increase in the dose. Visual readings of erythema and pigmentation were performed at 10 min, 2 h and 24 h after the UVA1 irradiation. Colorimetric measurements were taken to determine erythema (a* value) and pigmentation (L* value) objectively.
  
  
  RESULTS
  More than 30% (18 of 59) of the participants had a high-dose UVA1-MED (> 70-130 J cm-2); 56% (33) had no detectable UVA1-MED after 24 h and eight (14%) had a medium-dose UVA1-MED (20-70 J cm-2). We observed a stepwise decrease of the a* value measured at the UVA1-MED skin site from 10 min to 2 h and 24 h (P < 0·001). In contrast, there was a stepwise increase of the L* value measured at the UVA1-MED skin site from 10 min to 2 h and 24 h (P < 0·001).
  
  
  CONCLUSIONS
  Most participants had no measurable UVA1-MED even after commencing high doses such as 130 J cm-2. Only a minority of participants (14%) may develop UVA1-induced erythema in the low- and medium-dose region. Hence, it appears to be safe to start UVA1 phototherapy with 20 J cm-2of UVA1 and continue with subsequent daily dose increments of 10 J cm-2, up to the desired maximum dose.
authors.affiliation: Department of Dermatology, Ruhr-University Bochum, Gudrunstrasse 56, Bochum, 44791, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Gambichler
authors.affiliation: Department of Dermatology, Ruhr-University Bochum, Gudrunstrasse 56, Bochum, 44791, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Majert
authors.affiliation: Department of Dermatology, Ruhr-University Bochum, Gudrunstrasse 56, Bochum, 44791, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Pljakic
authors.affiliation: Department of Dermatology, Ruhr-University Bochum, Gudrunstrasse 56, Bochum, 44791, Germany.
authors.forename: I
authors.initials: I
authors.lastname: Rooms
authors.affiliation: Research Unit for Photodermatology, Department of Dermatology, Medical University of Graz, Graz, Austria.
authors.forename: P
authors.initials: P
authors.lastname: Wolf
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D004307:Dose-Response Relationship, Radiation; D004890:Erythema / Q000209:etiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010859:Pigmentation Disorders / Q000209:etiology; D011446:Prospective Studies; D011829:Radiation Dosage; D012871:Skin Diseases / Q000628:therapy; D014466:Ultraviolet Rays / Q000009:adverse effects*; D014467:Ultraviolet Therapy / Q000009:adverse effects; D055815:Young Adult