An action spectrum for the production of cis-urocanic acid in human skin in vivo

Pauline McLoone, Eniko Simics, Alan Barton, Mary Norval, Neil K. Gibbs

Research output: Contribution to journalArticlepeer-review

49 Citations (Scopus)


Urocanic acid (UCA) is present at millimolar concentrations in mammalian epidermis and undergoes photo-isomerization from the naturally occurring trans-isomer to the cis-isomer on exposure to ultraviolet radiation (UVR). Cis-UCA causes downregulation of various immune responses in mouse and human experimental models and has been proposed as both a chromophore and a mediator of UV-induced immune suppression. In this study, the wavelength dependence from 260-340 nm for trans to cis-UCA photoisomerization in human skin was analyzed in five healthy volunteers. The resulting action spectrum demonstrated maximal cis-UCA production in the UVB spectral region of 280-310 nm. This spectral peak is red-shifted to longer wavelengths compared with the erythemal action spectrum. The cis-UCA action spectrum can be used to predict the ability of sunscreens to protect against UVR-induced cis-UCA formation and may assist in explaining discrepancies between sunscreens' abilities to protect against erythema and photoimmunosuppression.

Original languageEnglish
Pages (from-to)1071-1074
Number of pages4
JournalJournal of Investigative Dermatology
Issue number5
Publication statusPublished - May 2005


  • Skin
  • UV radiation
  • Urocanic acid

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Dermatology
  • Cell Biology

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