Coal Tar
Coal tar is a very old and very effective remedy with a great deal of research showing its success for many forms of psoriasis. Coal tar is a topical medication available both over the counter and by prescription; the difference between the two options is in the potency and amount of coal tar the medication contains. Coal tar inhibits certain skin substances that trigger cell proliferation, thus reducing the appearance of psoriasis. Enhanced benefit can be seen when coal tar is combined with UV light exposure. Referred to as the Goeckerman regimen, it involves the dermal application of a crude coal tar (polycyclic aromatic hydrocarbon) and exposure to ultraviolet radiation. Coal tar can be combined with other psoriasis medications like topical steroids. (Source: International Journal of Dermatology, August 2008, pages 800-805.)
Because coal tar can make the skin more sensitive to UV light, extreme caution is advised when you combine coal tar use with UV therapy (or exposure to the sun) to avoid getting a severe burn or causing significant skin damage. Other downsides to coal tar are the irritation it can cause, the unpleasant smell, and its tendency to stain clothes.