Photoallergy to hexamidine.

This report details the case of an atopic patient showing a photosensitivity caused by a hexamidine solution. Patch tests were negative but photopatch tests to hexamidine in water solution were positive, after irradiation by ultraviolet A (UVA); all control tests were negative. It is well-known that hexamidine can induce contact allergy but this case was the first reported in which UVA was implicated. This photoallergy can be explained by the structure of the hexamidine molecule, but the question is: why has there never been such a case reported before?