A chronic, non-contagious disease, psoriasis [pronounced sore-EYE-ah-sis] varies in its severity and how it responds to treatment. It results from inappropriate responses of the body's immune system to essentially attack the body itself and can occur on any part of the body that's covered by skin. The resulting inflammation can be as mild as something resembling dandruff or as radical as a body covered with thick, crusted plaques. Less than 10 percent of sufferers have an extreme form of the disease; it is a mild form in 65 percent of cases. Everything else is in between mild and serious. Though it usually doesn't get any worse over time, about 10 percent to 30 percent of people with psoriasis also develop psoriatic arthritis, which causes pain, stiffness and swelling in and around the joints.

Psoriasis is a disease which takes different forms, including:

Scalp psoriasis

At least half of all people who have psoriasis have it on their scalp. As with psoriasis elsewhere on the body, skin cells grow too quickly and cause red lesions covered with scale. In severe cases of thick, crusted plaques covering the entire scalp, the hair may fall out. The affected area can extend beyond the hairline onto the forehead, the back of the neck and around the ears. Treatments, as with any type of psoriasis, are often combined and rotated because it can become resistant to medications after repeated use. Many treatment options can help control scalp psoriasis and its symptoms:

Tar products and salicylic acid are generally sufficient for treating very mild scalp psoriasis.

Ultraviolet (UV) light treatments.

Systemic (oral or injected) treatments may be tried if psoriasis is present elsewhere on the body and/or the psoriasis is severe.

Topical medications (applied to the skin).

Genital psoriasis Although it usually responds well to various treatments, the sensitive nature of the skin around the genitals requires a cautious approach to genital psoriasis:

• Ultraviolet (UV) light. Overexposure to UV light can burn the skin, especially the thinner skin around the genitals, so it is therefore used only in special circumstances and in very low doses.

Protopic and Elidel. Both of these drugs reduce skin inflammation much as topical steroids do, but they do not cause thinning of the skin. They may cause some irritation when they are first used, but they do not promote yeast or bacterial growth, which may further help with inflammation and itching.

Psoriasis in the pubic area may respond well to UV light treatment if the pubic hair is cut short or shaved. Men should wear briefs or athletic supporters to protect their genitals while receiving UV light treatment on other parts of the body.

Dovonex. Though this synthetic form of vitamin D3 has the potential for irritation, it does not have any of the drawbacks of topical steroids, and mixing it with petroleum jelly may minimize irritation.

Tazorac. Because of its potential for irritation, some doctors alternate its use with a low-strength topical steroid.

Over-the-counter (OTC) moisturizers. The skin in affected genital areas should be continuously moisturized, but choose wisely: moisturizers with fragrance and perfumes may irritate.

Steroids. Prolonged use of topical steroids can permanently thin the skin and cause stretch marks. Furthermore, psoriasis may become resistant to clearing with continuous long-term use of steroids.

Facial psoriasis Areas of the face most often affected are the eyebrows, the skin between the nose and upper lip, the upper forehead, and the hairline. Because other skin diseases resemble the symptoms of psoriasis on the face, a biopsy may be needed to positively identify it.

Psoriasis scaling can also block the ear canal and produce temporary hearing loss; it should be removed by a doctor. Psoriasis in and around the mouth or on the lips causes discomfort and may present difficulty in chewing and swallowing food. Improving hygiene and rinsing frequently with a saline solution can help relieve oral discomfort, and there are effective topical steroids that have been designed to treat moist areas.

Rashes may also appear on the eyelids, around the ears, mouth, and on the nose. Treating eyelid inflammation may involve washing the edges of the eyelids and eyelashes with a solution of water and baby shampoo. An over-the-counter product, Ocusoft, can help with removing scales on the lids and eye margins. But a doctor must carefully supervise the treatment because eyelid skin can be easily damaged, and the use of topical steroids there can lead to glaucoma and/or cataracts.

In addition to Dovonex, Tazorac, and ultraviolet light, Protopic may be used in treating facial psoriasis. This and Elidel, both drugs used to treat eczema, have also been found effective in treating psoriasis. Topical steroids may be used, but prolonged use of them may cause enlarged capillaries (spider veins) on the face.

Psoriasis lesions, usually white or gray, may also appear on the gums, the tongue, inside the cheek, or inside the nose.