Tar shampoo alone is not recommended for treatment of severe scalp psoriasis (ie where there is thick scaling and redness). In some cases, psoriasis can be hard to treat if it is severe and widespread. Topical agents: Medications applied directly to the psoriatic skin lesions are the safest approaches to treatment but are only practical if treating localized disease. More serious cases might need more aggressive treatment. It can appear anywhere on the body but is most commonly found on the scalp, knees, elbows, and torso.