Psoriderm Emulsion Bath Additive Psoriderm Emulsion Bath Additive is designed to help treat sub-acute or chronic plaque psoriasis. This type of psoriasis involves areas of raised, red, sometimes itchy, patches of skin, covered with silvery scales (without any blistering or tenderness) & often occurs on the elbows, knees, lower back & scalp. Psoriderm Emulsion Bath Additive contains distilled coal tar, which stops itching & restores normal skin development. Psoriderm Emulsion Bath Additive can be used by adults, the elderly & children.