Dendropanax trifidus Makino (family Araliaceae, syn. Gilibertia trifida Makino) has been reported as causing allergic contact dermatitis in Japan. To identify the major allergen, fractionated extracts of fresh leaves of Dendropanax trifidus were patch tested on 2 patients with hypersensitivity to
cis-9,17-Octadecadiene-12,14-diyne-1,16-diol (I), an analog of falcarinol has been identified in our previous report as an active component of Dendropanax trifidus and a strong sensitizer. In this report, 16-hydroxy-cis-9,17-octadecadiene-12,14-diynoic acid (II) and