Cis-Urocanic acid
cis-Urocanic acid is a chemical compound produced by ultraviolet irradiation of trans-urocanic acid, a metabolite naturally formed in the body from histidine. cis-Urocanic acid is suspected of involvement in the development of skin cancer. It acts as an immunosuppressant through action as an agonist of the 5-HT2A receptor, and blocking this receptor has been shown to reduce cis-UCA mediated photocarcinogenesis. However the immunomodulatory effects of cis-UCA are complex and also involve other pathways, and at low levels it shows antiinflammatory actions and may be protective against UV damage in the cornea and retina. Measuring cis-UCA has been proposed as a sensitive method to detect sub-erythemal response to UVB, and thus a means to assess the UVR protection of suncreams.