(LifeWire) - It is smelly and greasy and stains clothing, so why do people with psoriasis still use coal tar products as a treatment for psoriasis?
Because coal tar, one of the few remaining old-fashioned therapies for this condition, still does the job. Within a few weeks of applying ointments, creams or shampoos containing coal tar, psoriasis patients (called "psoriatics") can usually expect their lesions to clear significantly.
Approximately 2% of the U.S. population - roughly 6 million people of all ages - have psoriasis, an immune system disorder that causes skin cells to turn over about 10 times faster than normal. The resulting scaly, red patches can appear on any part of the body, including the palms, soles of the feet or genitals.
Coal tar, while still useful for the two-thirds of psoriatics who have a mild-to-moderate form of the disease, though, is no longer a first-line treatment for more severe cases. The first choice for such patients is generally one of the systemic, injectable medications known as biologics.
"Tar was one of the oldest things used for psoriasis," says Doris J. Day, MD, clinical assistant professor of dermatology at New York University Medical Center. "People used to take tar baths - it was disgusting. With biologics, their use is much reduced, to the point where I don't [prescribe] them much at all anymore."
But the effectiveness and availability of coal tar in over-the-counter (OTC) forms make it a logical choice for individuals whose psoriasis is limited to several well-defined areas. In particular, Day says, patients with plaque psoriasis, the most common of the five types of skin lesions associated with psoriasis, find coal tar especially helpful.
A thick brown or black liquid, tar can be made from wood or coal. The coal version is most commonly used in psoriasis treatment. By slowing the overgrowth of skin cells and reducing inflammation, it improves itching and skin appearance.
OTC coal tar is available in strengths ranging from 0.5% to 5% and is readily found at pharmacies. The stronger versions fight psoriasis more aggressively, but they also smell worse.
The odor of tar is perhaps the greatest annoyance, quickly followed - in many products - by a heavy, greasy consistency. Doctors often advise patients to use tar medications at night, allowing the medication to sit on the skin, covered over with old clothing or socks. This helps prevent stained pajamas and bed sheets.
Coal tar has other drawbacks as well: Tar preparations, for example, are harder to find in California, because the state's requirement is that all products with more than .5% coal tar carry warnings of potential cancer. The National Psoriasis Foundation recommends that anyone using coal tar recognize the signs of skin cancer and report any suspicious lesions to their dermatologist, visit http://www.psoriasis.org/treatment/psoriasis/topicals/tar.php. Also, coal tar can irritate or redden the skin, so before using it, test a small spot on the back of your wrist to gauge your reaction. Since tar-treated skin is very sun-sensitive, your dermatologist may recommend keeping tar-treated skin out of the sunlight all together. In addition, tar shampoos often need to be left on the scalp for up to 10 minutes before rinsing and can leave an unpleasant smell afterward. Be sure to follow up the tar shampoo with a more pleasingly scented shampoo or conditioner.The good news: Despite concerns that OTC coal tar products may be cancerous, the U.S. Food and Drug Administration has found no evidence of any problems among those who use such products. Be sure, though, to remember that coal tar is made up of more than 10,000 ingredients, and medications that contain coal tar can vary widely in both their effects and effectiveness.
"Coal Tar for Psoriasis." Patient UK. 21 Feb 2008. Patient UK. 27 May 2008. <http://www.patient.co.uk/showdoc/27001373.>
Doris J. Day, MD, clinical assistant professor of dermatology, NYU Medical Center. Phone interview. 16 May 2008.
"Tar: What Is Tar and How Does It Work?" Psoriasis.org. June 2006. National Psoriasis Foundation. 21 April 2008. <http://www.psoriasis.org/treatment/psoriasis/topicals/tar.php>.