Psoriasis is a chronic, inflammatory skin disease. Knees, elbows, scalp, trunk, and nails are the most commonly affected areas. There are several types of psoriasis.
• Plaque--inflamed patches of skin topped with silvery, white scales (most common type)
• Guttate--small dot-like lesions
• Pustular--weeping lesions and intense scaling
• Erythrodermic--intense sloughing and inflammation of the skin

The cause of psoriasis is unclear. Signals from a defect in the immune system may result in an overgrowth of skin cells. Because the cells grow faster than they can be shed, they ‘pile up' on the skin's surface. The excess skin cells are thought to cause the silvery white scales that are characteristic of plaque-type psoriasis.
Risk Factors
A risk factor is something that increases your chance of getting a disease or condition.
• Sex: Female
• Family history of psoriasis
• Rheumatoid arthritis
• Cold climates
• Suppression of the immune system, including AIDS
• Certain bacterial infections
• Certain medications, such as beta blockers and lithium
The red, thickened and rough patches of psoriasis may occur anywhere, but are commonly found on the scalp, elbows, knees, palms, and soles. Other symptoms include:
• Silvery white scales
• Pitted or dented fingernails and/or toenails
• Red lesion in the folds of the buttock
• Joint pain suggesting arthritis
The doctor will ask about your symptoms and medical history, and perform a physical exam. Your skin and nails will be examined. There are no specific blood tests or diagnostic procedures for psoriasis. Sometimes a skin biopsy will be done to confirm the diagnosis.
Treatment is based on:
• The severity of the disease
• The extent and location of the areas involved
• Responsiveness to the treatment
Topical Treatment
Many patients respond very well to treatments applied directly to the skin. Topical treatments include:
• Corticosteroid creams (most common treatment)
• Synthetic forms of vitamin D and retinoids (calcipotriene ointment 0.005??)
• Retinoids (tazarotene gel 0.05 and 0.1%)
• Coal tar preparations
• Bath solutions and moisturizers
Photo (Light) Therapy
If psoriasis covers more than 30% of the body it is difficult to treat with topical medications alone. Daily, short, nonburning exposure to sunlight clears or improves psoriasis in many people. Sunlight is often included among initial treatments. A more controlled form of artificial light treatment (UVB phototherapy) is often used in more widespread but mild cases. More severe psoriasis can be treated with ultraviolet A (UVA light) and psoralen. Psoralen is an oral or topical medication that makes the body more sensitive to light. This treatment is known as PUVA.
Phototherapy can be very effective in controlling psoriasis but it requires frequent treatments. It may cause side effects such as nausea, headache, fatigue, burning, and itching. Both UVB and PUVA may increase the person's risk for squamous cell and, possibly, melanoma skin cancers.
Systemic Treatment
For more severe types of psoriasis, doctors may prescribe a number of other powerful medications, which can be effective, but are associated with more serious side effects. These include:
• Methotrexate--should not be taken by pregnant women, women planning to become pregnant, or by their male partners.
• Cyclosporine--suppresses the immune system to slow the turnover of skin cells.
• Hydroxyurea--less toxic than methotrexate or cyclosporine, but may less effective.
• Systemic Retinoids--compounds with vitamin A-like properties taken internally (such as methotrexate) may be prescribed in severe cases. Retinoids can cause birth defects and women must diligently protect themselves from pregnancy for several years after completing treatment.
Newer systemic immunomodulators, so called because they affect some aspect of the body’s natural immune response, may also be quite effective. These treatments are generally the most expensive, however, and some can cause serious toxicity when given systemically (by mouth or injection). Topical preparations of immunomodulators are currently being tested and seem to have benefits. Other drugs called thiazolidinediones may show promise as future treatments for psoriasis but are not currently recommended.
Although the condition of psoriasis cannot be prevented, people at increased risk for the condition (ie, family history of psoriasis) should try to avoid physical trauma to the skin, infections, and temperature extremes.
These measures may also help reduce flare-ups in people with the condition. Your doctor may advise you to avoid certain foods if they appear to make your psoriasis worse.