Coal tar is an old school treatment option that can decrease the rate of skin cell production and help restore skin’s appearance. It’s a double-edged sword, though. While it can help reduce the inflammation, itching and scaling of psoriasis, it can also increase sensitivity to UV light and irritate skin. (Not to mention it has the ability to stain clothes and it leaves you smelling like coal tar.) Studies show some of the chemicals in coal tar may cause cancer but only in very high concentrations, such as the amounts used in industrial paving. The FDA maintains that OTC products with coal tar concentrations between 0.5 percent and 5 percent are safe and effective for psoriasis, and there is no scientific evidence that the tar in OTC products is carcinogenic (source: www.psoriasis.org). Still, you might as well consider other treatments without the potential side effects.