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Anthralin (Drithocreme and others) is an effective drug for psoriasis that has been used for almost a century. It was originally derived from the bark of the araroba tree. Anthralin works by affecting the growth of skin cells in the patches of psoriasis. It also reduces inflammation. The advantages of anthralin are that it works well, especially on hard to treat plaques, and it causes no serious side effects. The disadvantages are that it can irritate the skin and stains everything, including clothing, sheets, and even skin. Because of its drawbacks, it's seldom used. 

Coal tar has been a topical treatment for psoriasis since the nineteenth century. It's sold in many different forms, both with and without prescription, with strengths ranging from 0.5% to 5%. Tar shampoos are often helpful in treating psoriasis of the scalp. Other forms of coal tar, such as Psorent,  can be applied to the skin. Coal tar has a well-deserved reputation for being messy and smelly. It can also stain clothing and irritate the skin. However, coal tar products that are on the market now are much easier to use than they once were. Follow the directions carefully. Some studies have shown that the chemicals in coal tar are cancerous, but this is only true at very high doses. It's safe to use coal tar if you follow your doctor's instructions.

Salicylic acid is used to remove the scales that appear on patches of psoriasis. It's sold in lotions, gels, soaps, and shampoos. Salicylic acid is especially useful in combination with other topical treatments. By removing the flakes of dead skin, salicylic acid allows these other medications to better penetrate the lesions. 

Moisturizers and lotions sold over the counter can keep your skin moist and help control flare-ups in mild cases of psoriasis. In general, the greasier lotions that trap moisture in your skin work better.

Calcineurin inhibitors. Tacrolimus and pimecrolimus can also be used to treat psoriasis. They are generally well tolerated. However, a black box warning has been placed on the prescribing information for these drugs because of a possible link between these medications and cases of lymphoma and skin cancer.  

Limitations of Topical Psoriasis Treatments

Treating psoriasis with topical ointments and creams is an imprecise science. You may find that an approach works for a while, then stops working. Another cream that never worked before may suddenly start helping.

Because a lot of these topical treatments can irritate your skin and may become less effective over time, your doctor may suggest that you cycle through different types of creams. Topical treatments are also frequently used in combination with each other and with phototherapy or oral medications. While occlusion -- applying a topical treatment and then wrapping the area in tape or plastic wrap -- is appropriate with some drugs in some cases, it should not be used with others. Check with your doctor.

Using topical treatments can be difficult. Coal tar doesn't smell good, many of the creams and ointments can be greasy, and quite a few can stain clothing or skin. Scalp treatments may require that you sleep in a shower cap. Make sure that you understand the directions for taking your medication and their potential side effects before you start using them.

If you don't like a treatment -- because it causes side effects or because you find using it difficult -- be sure to talk to your doctor about a substitution. If you don't use your medication regularly, your psoriasis may get worse.

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