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Publication Date: September 1999
Last Update: January 2002

Questions and Answers About Psoriasis

What Is Psoriasis?

Psoriasis is a chronic (long-lasting) skin disease characterized by scaling and inflammation. Scaling occurs when cells in the outer layer of the skin reproduce faster than normal and pile up on the skin’s surface.

Psoriasis affects between 1 and 2 percent of the United States population, or about 5.5 million people. Although the disease occurs in all age groups and about equally in men and women, it primarily affects adults. People with psoriasis may suffer discomfort, including pain and itching, restricted motion in their joints, and emotional distress.

In its most typical form, psoriasis results in patches of thick, red skin covered with silvery scales. These patches, which are sometimes referred to as plaques, usually itch and may burn. The skin at the joints may crack. Psoriasis most often occurs on the elbows, knees, scalp, lower back, face, palms, and soles of the feet but it can affect any skin site. The disease may also affect the fingernails, the toenails, and the soft tissues inside the mouth and genitalia. About 15 percent of people with psoriasis have joint inflammation that produces arthritis symptoms. This condition is called psoriatic arthritis.  

What Causes Psoriasis?

Recent research indicates that psoriasis is likely a disorder of the immune system. This system includes a type of white blood cell, called a T cell, that normally helps protect the body against infection and disease. Scientists now think that, in psoriasis, an abnormal immune system causes activity by T cells in the skin. These T cells trigger the inflammation and excessive skin cell reproduction seen in people with psoriasis.

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In about one-third of the cases, psoriasis is inherited. Researchers are studying large families affected by psoriasis to identify a gene or genes that cause the disease. (Genes govern every bodily function and determine the inherited traits passed from parent to child.)

People with psoriasis may notice that there are times when their skin worsens, then improves. Conditions that may cause flareups include changes in climate, infections, stress, and dry skin. Also, certain medicines, most notably beta-blockers, which are used to treat high blood pressure, and lithium or drugs used to treat depression, may trigger an outbreak or worsen the disease.

How Is Psoriasis Diagnosed?

Doctors usually diagnose psoriasis after a careful examination of the skin. However, diagnosis may be difficult because psoriasis can look like other skin diseases. A pathologist may assist with diagnosis by examining a small skin sample (biopsy) under a microscope.

There are several forms of psoriasis. The most common form is plaque psoriasis (its scientific name is psoriasis vulgaris). In plaque psoriasis, lesions have a reddened base covered by silvery scales. Other forms of psoriasis include

  • Guttate psoriasis--Small, drop-like lesions appear on the trunk, limbs, and scalp. Guttate psoriasis is most often triggered by bacterial infections (for example, Streptococcus).

  • Pustular psoriasis--Blisters of noninfectious pus appear on the skin. Attacks of pustular psoriasis may be triggered by medications, infections, emotional stress, or exposure to certain chemicals. Pustular psoriasis may affect either small or large areas of the body.

  • Inverse psoriasis--Large, dry, smooth, vividly red plaques occur in the folds of the skin near the genitals, under the breasts, or in the armpits. Inverse psoriasis is related to increased sensitivity to friction and sweating and may be painful or itchy.

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  • Erythrodermic psoriasis--Widespread reddening and scaling of the skin is often accompanied by itching or pain. Erythrodermic psoriasis may be precipitated by severe sunburn, use of oral steroids (such as cortisone), or a drug-related rash.

What Treatments Are Available for Psoriasis?

Doctors generally treat psoriasis in steps based on the severity of the disease, the extent of the areas involved, the type of psoriasis, or the patient’s responsiveness to initial treatments. This is sometimes called the “1-2-3” approach. In step 1, medicines are applied to the skin (topical treatment). Step 2 focuses on light treatments (phototherapy). Step 3 involves taking medicines internally, usually by mouth (systemic treatment).

Over time, affected skin can become resistant to treatment, especially when topical corticosteroids are used. Also, a treatment that works very well in one person may have little effect in another. Thus, doctors commonly use a trial-and-error approach to find a treatment that works, and they may switch treatments periodically (for example, every 12 to 24 months) if resistance or adverse reactions occur. Treatment depends on the location of lesions, their size, the amount of the skin affected, previous response to treatment, and patients’ perceptions about their skin condition and preferences for treatment. In addition, treatment is often tailored to the specific form of the disorder.

Topical Treatment

Treatments applied directly to the skin are sometimes effective in clearing psoriasis. Doctors find that some patients respond well to sunlight, corticosteroid ointments, medicines derived from vitamin D3, vitamin A (retinoids), coal tar, or anthralin. Other topical measures, such as bath solutions and moisturizers, may be soothing but are seldom strong enough to clear lesions over the long term and may need to be combined with more potent remedies.

  • Sunlight--Daily, regular, short doses of sunlight that do not produce a sunburn clear psoriasis in many people.

  • Corticosteroids--Available in different strengths, corticosteroids (cortisone) are usually applied twice a day. Short-term treatment is often effective in improving but not completely clearing psoriasis. If less than 10 percent of the skin is involved, some doctors will begin treatment with a high-potency corticosteroid ointment (for example, Diprolene®,* Temovate®, Ultravate®, or Psorcon®). High-potency steroids may also be used for treatment-resistant plaques, particularly those on the hands or feet. Long-term use or overuse of high-potency steroids can lead to worsening of the psoriasis, thinning of the skin, internal side effects, and resistance to the treatment’s benefits. Medium-potency corticosteroids may be used on the torso or limbs; low-potency preparations are used on delicate skin areas.

    *Brand names included in this fact sheet begin with a capital letter and are provided as examples only. Their inclusion does not mean that these products are endorsed by the National Institutes of Health or any other Government agency. Also, if a particular brand name is not mentioned, this does not mean or imply that the product is unsatisfactory.

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  • Calcipotriene--This drug is a synthetic form of vitamin D3. (It is not the same as vitamin D supplements.) Applying calcipotriene ointment (for example, Dovonex®) twice a day controls excessive production of skin cells. Because calcipotriene can irritate the skin, however, it is not recommended for the face or genitals. After 4 months of treatment, about 60 percent of patients have a good to excellent response. The safety of using the drug for cases affecting more than 20 percent of the skin is unknown, and using it on widespread areas of the skin may raise the amount of calcium in the body to unhealthy levels.

  • Coal tar--Coal tar may be applied directly to the skin, used in a bath solution, or used on the scalp as a shampoo. It is available in different strengths, but the most potent form may be irritating. It is sometimes combined with ultraviolet B (UVB) phototherapy. Compared with steroids, coal tar has fewer side effects, but it is messy and less effective and thus is not popular with many patients. Other drawbacks include its failure to provide long-term help for most patients, its strong odor, and its tendency to stain skin or clothing.

  • Anthralin--Doctors sometimes use a 15- to 30-minute application of anthralin ointment, cream, or paste to treat chronic psoriasis lesions. However, this treatment often fails to adequately clear lesions, it may irritate the skin, and it stains skin and clothing brown or purple. In addition, anthralin is unsuitable for acute or actively inflamed eruptions.

  • Topical retinoid--The retinoid tazarotene (Tazorac) is a fast-drying, clear gel that is applied to the surface of the skin. Although this preparation does not act as quickly as topical corticosteroids, it has fewer side effects. Because it is irritating to normal skin, it should be used with caution in skin folds. Women of childbearing age should use birth control when using tazarotene.

  • Salicylic acid--Salicylic acid is used to remove scales, and is most effective when combined with topical steroids, anthralin, or coal tar.

  • Bath solutions--People with psoriasis may find that bathing in water with an oil added, then applying a moisturizer, can soothe their skin. Scales can be removed and itching reduced by soaking for 15 minutes in water containing a tar solution, oiled oatmeal, Epsom salts, or Dead Sea salts.

  • Moisturizers--When applied regularly over a long period, moisturizers have a cosmetic and soothing effect. Preparations that are thick and greasy usually work best because they hold water in the skin, reducing the scales and the itching.

Phototherapy

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Ultraviolet (UV) light from the sun causes the activated T cells in the skin to die, a process called apoptosis. Apoptosis reduces inflammation and slows the overproduction of skin cells that causes scaling. Daily, short, nonburning exposure to sunlight clears or improves psoriasis in many people. Therefore, sunlight may be included among initial treatments for the disease. A more controlled form of artificial light treatment may be used in mild psoriasis (UVB phototherapy) or in more severe or extensive psoriasis (psoralen and ultraviolet A [PUVA] therapy).

UVB phototherapy--Some artificial sources of UVB light are similar to sunlight. Newer sources, called narrow-band UVB, emit the part of the ultraviolet spectrum band that is most helpful for psoriasis. Some physicians will start with UVB treatments instead of topical agents. UVB phototherapy is also used to treat widespread psoriasis and lesions that resist topical treatment. This type of phototherapy is normally administered in a doctor’s office by using a light panel or light box, although some patients can use UVB light boxes at home with a doctor’s guidance. Generally at least three treatments a week for 2 or 3 months are needed. UVB phototherapy may be combined with other treatments as well. One combined therapy program, referred to as the Ingram regime, involves a coal tar bath, UVB phototherapy, and application of an anthralin-salicylic acid paste, which is left on the skin for 6 to 24 hours. A similar regime, the Goeckerman treatment, involves application of coal tar ointment and UVB phototherapy.

PUVA--This treatment combines oral or topical administration of a medicine called psoralen with exposure to ultraviolet A (UVA) light. Psoralen makes the body more sensitive to this light. PUVA is normally used when more than 10 percent of the skin is affected or when rapid clearing is required because the disease interferes with a person’s occupation (for example, when a model’s face or a carpenter’s hands are involved). Compared with UVB treatment, PUVA treatment taken two to three times a week clears psoriasis more consistently and in fewer treatments. However, it is associated with more short-term side effects, including nausea, headache, fatigue, burning, and itching. Long-term treatment is associated with an increased risk of squamous cell and melanoma skin cancers. PUVA can be combined with some oral medications (retinoids and hydroxyurea) to increase its effectiveness. Simultaneous use of drugs that suppress the immune system, such as cyclosporine, have little beneficial effect and increase the risk of cancer. In very rare cases, patients who must travel long distances for PUVA treatments may, with a physician’s close supervision, be taught to administer this treatment at home.

Systemic Treatment

For more severe forms of psoriasis, doctors sometimes prescribe medicines that are taken internally:

  • Methotrexate--This treatment, which can be taken by pill or injection, slows cell production by suppressing the immune system. Patients taking methotrexate must be closely monitored because it can cause liver damage and/or decrease the production of oxygen-carrying red blood cells, infection-fighting white blood cells, and clot-enhancing platelets. As a precaution, doctors do not prescribe the drug for people with long-term liver disease or anemia. Methotrexate should not be used by pregnant women, by women who are planning to get pregnant, or by their male partners.

  • Cyclosporine--Taken orally, cyclosporine (Neoral®) acts by suppressing the immune system in a way that slows the rapid turnover of skin cells. It may provide quick relief of symptoms, but it is usually effective only during the course of treatment. The best candidates for this therapy are those with severe psoriasis who have not responded to or cannot tolerate other systemic therapies. Cyclosporine may impair kidney function or cause high blood pressure (hypertension), so patients must be carefully monitored by a doctor. Also, cyclosporine is not recommended for patients who have a weak immune system, those who have had substantial exposure to UVB or PUVA in the past, or those who are pregnant or breast-feeding.

  • Hydroxyurea (Hydrea®)--Compared with methotrexate and cyclosporine, hydroxyurea is less toxic but also less effective. It is sometimes combined with PUVA or UVB. Possible side effects include anemia and a decrease in white blood cells and platelets. Like methotrexate and cyclosporine, hydroxyurea must be avoided by pregnant women or those who are planning to become pregnant.

  • Retinoids--A retinoid, such as acitretin (Soriatane®), is a compound with vitamin A-like properties that may be prescribed for severe cases of psoriasis that do not respond to other therapies. Because this treatment also may cause birth defects, women must protect themselves from pregnancy beginning 1 month before through 3 years after treatment. Most patients experience a recurrence of psoriasis after acitretin is discontinued.

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  • Antibiotics--Although not indicated in routine treatment, antibiotics may be employed when an infection, such as Streptococcus, triggers the outbreak of psoriasis, as in certain cases of guttate psoriasis.

What Are Some Promising Areas of Psoriasis Research?

Researchers continue to search for genes that contribute to the inherited and other causes of psoriasis. Scientists are also working to improve our understanding of what happens in the body to trigger this disease. In addition, much research is focused on developing new and better treatments. Some of these experimental treatments, such as agents directed at the specific types of T cells involved, work to improve the disease with less overall suppression of the immune system.

How Can People Contribute to Psoriasis Research?

The National Psoriasis Tissue Bank, which is supported by the National Psoriasis Foundation, is helping researchers worldwide study the inherited tendency toward psoriasis. The tissue bank has DNA from the white blood cells of more than 250 families affected by the disease. There is particular interest in large families in which psoriasis is both common and spans two or more generations. More recently, the tissue bank has begun research involving families having at least two siblings with psoriasis. People seeking more information or families interested in participating in a study should contact

  • National Psoriasis Foundation Tissue Bank
    6600 SW 92nd Avenue
    Suite 300
    Portland, OR 97223-7195
    503/244-7404
    800/723-9166
    Fax: 503/245-0626
    World Wide Web address: http://www.psoriasis.org

Where Can People Find More Information About Psoriasis?

  • National Psoriasis Foundation
    6600 SW 92nd Avenue, Suite 300
    Portland, OR 97223-7195
    503/244-7404
    800/723-9166
    Fax: 503/245-0626
    World Wide Web address: http://www.psoriasis.org

The National Psoriasis Foundation provides physician referrals and publishes pamphlets and newsletters that include information on support groups, research, and new drugs and other treatments. The foundation also promotes community awareness of psoriasis.

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    • National Institute of Arthritis and Musculoskeletal and Skin Diseases Information Clearinghouse
      1 AMS Circle
      Bethesda, MD 20892-3675
      301/495-4484
      TTY: 301/565-2966
      Fax: 301/718-6366
      NIAMS Fast Facts--For health information that is available by fax 24 hours a day, call 301/881-2731 from a fax machine telephone.
      World Wide Web address: http://www.niams.nih.gov/

    This clearinghouse, a public service sponsored by the National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS), provides information about various forms of these diseases. The clearinghouse distributes patient and professional education materials and also refers people to other sources of information.

    Acknowledgments

    The NIAMS gratefully acknowledges the assistance of Alan N. Moshell, M.D., of NIAMS; Gerald G. Krueger, M.D., of the University of Utah; Robert Stern, M.D., of Beth Israel Deaconess Medical Center in Boston, MA; and the National Psoriasis Foundation in the review and update of this fact sheet.

    The National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS), a part of the National Institutes of Health (NIH), leads the Federal medical research effort in arthritis and musculoskeletal and skin diseases. The NIAMS supports research and research training throughout the United States, as well as on the NIH campus in Bethesda, MD, and disseminates health and research information. The National Institute of Arthritis and Musculoskeletal and Skin Diseases Information Clearinghouse is a public service sponsored by the NIAMS that provides health information and information sources. Additional information can be found on the NIAMS Web site at http://www.niams.nih.gov/.

    Key Words

    Antibodies: Special proteins, produced by the body's immune system, that help fight and destroy viruses, bacteria, and other foreign substances that invade the body. 

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    Autoantibodies: Abnormal antibodies produced against the body's own tissues. 

    Autoimmune disease: A disease in which the immune system destroys or attacks a person's own tissues. 

    Cytokines: Chemical messengers in the body that help direct and regulate response and are involved in cell-to-cell communication. 

    Dermis: The layer of skin beneath the epidermis.

    Emollient: A substance composed of fat or oil that soothes and softens the skin. 

    Epidermis: The outermost layer of skin. 

    Erythrodermic psoriasis: A form of psoriasis characterized by widespread reddening and scaling of the skin often accompanied by itching or pain. Symptoms may be precipitated by severe sunburn, use of oral steroids, or a drug-related rash. 

    Gene: A unit of inheritance that contains the instructions, or code, that a cell uses to make a specific product, usually a protein. Genes are made of a substance called DNA. They govern every body function and determine inherited traits passed from parent to child.

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    Genetics: The science of understanding how diseases, conditions, and traits are inherited. 

    Guttate psoriasis: A form of psoriasis characterized by drop-like lesions on the trunk, limbs, and scalp. Symptoms may be triggered by viral respiratory infections or certain bacterial (streptococcal) infections. 

    Histologic examination: The study of a tissue specimen by staining it and examining it under a microscope. 

    Inflammation: A characteristic reaction of tissues to injury or disease. It is marked by four signs: swelling, redness, heat, and pain. 

    Immune response: The reactions of the immune system to foreign substances. 

    Immune system: A complex network of specialized cells and organs that work together to defend the body against attacks by foreign substances, such as bacteria and viruses. 

    Inverse psoriasis: A form of psoriasis characterized by large, dry, smooth, vividly red plaques in the folds of skin. 

    Keratolytic: A substance that promotes the softening and peeling of the epidermis. 

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    Phototherapy: Use of natural or artificial light to treat a disease. 

    Plaques: Patches of thickened and reddened skin that are covered by silvery scales. 

    Psoriasis: A chronic (long-lasting) skin disease characterized by scaling and inflammation. Scaling occurs when cells in the outer layer of skin reproduce faster than normal and pile up on the skin's surface. Possibly a disorder of the immune system. 

    Psoriasis vulgaris: The most common form of psoriasis, characterized by reddened lesions covered by silvery scales. 

    Psoriatic arthritis: Joint inflammation that occurs in about 10 percent of people with psoriasis. 

    PUVA: A treatment sometimes used for extensive or severe psoriasis that combines oral or topical administration of a medicine called psoralen with exposure to ultraviolet A (UVA) light. 

    Systemic treatment: A treatment, such as a pill, that is taken internally. 

    Topical agent: A treatment, such as a cream, salve, or ointment, that is applied to the surface of the skin. 

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    Toxicity: The potential of a drug or treatment to cause harmful side effects. 

    T cell: A type of white blood cell that is part of the immune system and normally helps protect the body against infection and disease. In psoriasis, it also can trigger inflammation and excessive skin cell reproduction. 

    UVB phototherapy: An artificial light treatment used for mild psoriasis.