Psoriasis was an irritating skin affliction.
In 2376, when Kathryn Janeway asked Tuvok to describe to the con artist Dala the "barbarity" of the Telsian prison system, Tuvok mentioned that torture and disease were commonplace, including "several incurable forms of psoriasis". Later, when Janeway questioned his choice of disease, Tuvok explained that he was not good at improvising. (VOY: "Live Fast and Prosper")