Be wary when harvesting rashvine because the plant comes by its name honestly. Indeed, calling its effect upon exposed skin a "rash" is an understatement. I've known apprentices who went without treating the red sores, assuming them irritating but harmless, and eventually required either magical healing or amputation.
Once the poison gets into the blood, it causes a painful calcification that turns the surface skin stone grey... and that's only the first symptom. In addition, it's primarily found in marshes and remote areas of deep vegetation, so there is often danger in finding rashvine patches, even aside from that in collecting it.
Fortunately (or unfortunately, if one happens to be a witless apprentice), rashvine has a number of useful applications: salves that harden the skin or otherwise provide protection, not to mention being one of the primary ingredients for Antivan fire. My advice? Use thick gloves and carry a sword.
—From Herbology in Thedas by Master Ilian Gravire