Psoriasis is a chronic skin disorder that causes areas of thickened, inflamed, red skin, often covered with silvery scales. Children and adolescents can develop psoriasis, but it occurs primarily in adults. Women and men are equally affected. Psoriasis is not an infection, and it is not contagious.
The severity of psoriasis is determined by how much of the body’s surface is covered and how much it affects a person's quality of life. Psoriasis is not curable, although many treatments are available to reduce the symptoms and appearance of the disease.
Researchers have not identified the exact cause of psoriasis. However, they believe that the disease develops due to a combination of immune, genetic, and environmental factors.
Immune system — The immune system plays an important role in the skin changes that occur in psoriasis. Understanding the normal process of skin development is helpful for understanding why skin changes occur in people with psoriasis.
The skin is made up of several layers (figure 1). The top layer is the epidermis, a layer of cells that divide and eventually die, covering the surface of the skin with a layer of dead cells called the stratum corneum. The middle layer is the dermis; this is the layer where collagen and blood vessels are found. The inner layer is the subcutaneous layer, a layer of fat underneath the skin. Every day, as cells in the epidermis die and become part of the stratum corneum, dead cells at the top of the stratum corneum also are shed. This balance prevents the dead skin layer from becoming too thick.
In skin affected by psoriasis, immune cells enter the skin through blood vessels and cause the epidermis to grow very rapidly and to stop shedding properly (figure 2). This causes thickening of the skin as well as the scaly build-up composed of dead skin cells that is seen on areas affected by psoriasis. Dilated blood vessels in the dermis that feed the rapidly growing epidermis cause the red color of the skin.
Genetics — Genetic factors play a role in determining whether someone develops psoriasis. About 40 percent of people with psoriasis or psoriatic arthritis (a type of arthritis closely related to psoriasis) have family members with the disorder (see "Patient information: Psoriatic arthritis (Beyond the Basics)"). Several genes have been identified that make people more susceptible to psoriasis, but there is no genetic test that can definitely tell whether an individual will develop the disease.
Environment and behavior — Environmental and behavioral factors can affect the risk of developing psoriasis or worsen psoriasis. Physical stress, psychological stress, or infections caused by bacteria or viruses can cause flares (worsening) of psoriasis symptoms. Certain medications also can worsen psoriasis symptoms, including beta blockers (eg, propranolol), lithium, and antimalarial drugs (eg, hydroxychloroquine, Plaquenil). Smoking appears to increase the risk and severity of psoriasis, particularly for psoriasis of the palms and soles.
Symptoms of psoriasis include:
- Areas of skin that are dry or red, usually covered with silvery-white scales, and sometimes with raised edges
- Rashes on the scalp, genitals, or in the skin folds
- Itching and skin pain
- Joint pain, swelling, or stiffness
- Nail abnormalities, such as pitted, discolored, or crumbly nails
TYPES OF PSORIASIS
There are several common types of psoriasis:
Plaque psoriasis — Plaque psoriasis is the most common form of psoriasis. Plaque psoriasis tends to affect young and middle aged adults, but can occur at any age. The individual skin plaques are usually between 0.4 and 4 inches [1 to 10 cm] wide, but may be larger. Some of the most common areas for plaques are the scalp, elbows, knees, and back (picture 1). The severity of plaque psoriasis varies widely. Plaque psoriasis may occur in just a few small areas or may cover a large portion of the body.
Guttate psoriasis — This type of psoriasis is sometimes linked to a recent streptococcal infection, usually pharyngitis (eg, strep throat). It often affects children or young adults with no past history of psoriasis, and causes a sudden eruption of small scaly papules on the trunk of the body (picture 2).
Pustular psoriasis — Pustular psoriasis can be a severe, and occasionally life-threatening, form of psoriasis. It develops quickly, with multiple small pustules that may join into larger areas (picture 3). Symptoms can include fever and abnormal blood levels of white blood cells and calcium. Pustular psoriasis can also cause pus-filled blisters on the palms of the hands and soles of the feet. These blisters can crack, causing painful breaks in the skin, and can be disabling.
Inverse psoriasis — This type of psoriasis affects less visible body areas, such as the groin, armpits, buttocks, genitals, and the area under the breasts (picture 4). Sometimes this is mistakenly diagnosed as a fungal or bacterial infection.
Nail psoriasis — Some people with psoriasis develop nail problems, including tiny pits over the surface of the nails. The pits look as if someone has taken a pin and pricked the nail several times (picture 5). In addition, nails may develop a tan-brown color (also known as “oil spots”) or may separate from the nail bed (also known as “onycholysis”) (picture 6). In more severe cases, people have thick, crumbling nails.
Treatment of nail psoriasis is difficult and may include injections of steroids into the nail bed or oral medications such as methotrexate, cyclosporine, or immunomodulatory drugs. (See 'Psoriasis treatment' below.)
Psoriatic arthritis — Up to one-third of people with psoriasis also have psoriatic arthritis, a condition that causes joint pain and swelling. Skin signs usually develop first, although about 15 percent of patients develop arthritis (joint swelling and stiffness) before symptoms of psoriasis. People with psoriatic arthritis often have severe nail problems. (See "Patient information: Psoriatic arthritis (Beyond the Basics)".)
Other associated conditions — There is a higher than normal frequency of depression in people with psoriasis. Psoriasis also has been associated with obesity and an increased risk of heart disease.
PSORIASIS DISEASE COURSE
Psoriasis is usually a lifelong condition and is not currently curable, although the severity of the disease can improve or worsen over time and can be controlled with treatment.
In people with certain forms of the disease, itching or pain and stiffness is severe and disabling. Some people with visible psoriasis lesions have feelings of embarrassment about their appearance. Stress, anxiety, loneliness, and low self-esteem can occur as a result.
People with psoriasis have higher rates of depression compared to those without the condition. People who have depression often benefit from working with a psychologist, clinical social worker, or other therapist to discuss their illness and identify possible ways to cope. A number of organizations, such as the National Psoriasis Foundation (www.psoriasis.org), are available to provide support to people with psoriasis and their families. (See 'Where to get more information' below.)
Psoriasis can be diagnosed by examining the skin. Occasionally, a skin biopsy or scraping may be taken to rule out other disorders. There is no blood test that can definitively diagnose psoriasis.
Psoriasis is not curable but many treatments are available that can reduce the bothersome symptoms and appearance of the disease. Treatment depends upon the severity of the disease, the cost and convenience of the treatment, and a person's response to the treatment. A combination of therapies is often recommended.
Referral to a dermatologist (a doctor who specializes in skin conditions) may be needed if the diagnosis of psoriasis is uncertain, if the initial treatment does not improve symptoms, or if the disease is widespread or severe. People with psoriatic arthritis may need to see a rheumatologist (a doctor who specializes in joint conditions).
Medicines applied to the skin — Many medications are available that can be rubbed onto the skin to treat psoriasis. Because psoriasis cannot be cured, continued use of medication is required to maintain improvement. For the best results, patients must use treatments as directed.
Emollients — Keeping skin soft and moist can minimize itching and tenderness. Over-the-counter moisturizers such as petroleum jelly or thick creams may be recommended; these should be applied immediately after bathing or showering.
Topical corticosteroids — Corticosteroids (sometimes called “steroids” but distinct from body building steroids) are applied to the skin to help to reduce inflammation. This is often done twice per day at the beginning of treatment. As a patient’s psoriasis improves, a doctor may recommend decreasing the frequency of treatment.
These cortisone-type creams and ointments are available in a variety of strengths (potencies); the least potent are available without a prescription (eg, hydrocortisone 1% cream) and are usually only effective in sensitive skin areas like the face and body folds. More potent formulations require a prescription. Other forms, such as solutions, gels, shampoo, lotion, foam, and spray, are available. Some people with psoriasis prefer these forms of medication over creams or ointments.
Side effects can include thinning of the skin and stretch marks (particularly when applied to normal skin). These effects are most likely to occur when topical corticosteroids are used for long periods of time. It is important to use these medications properly to reduce the risk for these side effects. A patient who notices these effects should contact his or her doctor.
Calcipotriene or calcitriol — Calcipotriene (Dovonex, Sorilux) and calcitriol (Vectical) are related to vitamin D and work by slowing the growth of skin cells in the epidermis. These medicines can be used instead of or in addition to topical corticosteroids. They are usually applied twice a day when used alone. The side effects are usually minimal, with skin irritation being the most common problem. These drugs do not cause thinning of the skin.
Another preparation, Taclonex, combines calcipotriene with a corticosteroid (betamethasone) in a once daily treatment. Although Taclonex is effective, it is quite expensive.
Tar — Tar is a substance distilled from coal that has been used to treat psoriasis for many years. It is not completely clear how tar works, although it appears to reduce the overproduction of skin cells that leads to psoriasis. Tar preparations are available in shampoos, creams, oils, and lotions without a prescription, and are usually applied to the skin or scalp once or twice a day. Tar products do not cause serious side effects, although they can stain skin, hair, and clothing. Tar products are often used along with corticosteroids or with ultraviolet light treatments. (See 'Ultraviolet light' below.)
Tazarotene — Tazarotene (Tazorac) is a skin treatment derived from vitamin A that is available in a cream or gel. It is usually applied once per day, in the evening. It may also be applied for 20 minutes and then washed off if skin irritation develops. Improvement should be seen within two months of treatment.
Calcineurin inhibitors — Topical calcineurin inhibitors, including tacrolimus (Protopic) and pimecrolimus (Elidel) creams, can be used to treat psoriasis, especially on the face and skin folds, such as in the armpits or under the breasts.
Anthralin — Anthralin is a treatment for psoriasis that has been used for psoriasis since the early 20th century. It is now used less commonly than many other medications because the treatment can cause temporary red-brown stains on skin and permanent stains on clothing. Because anthralin can be irritating, it is usually applied to the skin for only 10 to 60 minutes per day. Anthralin may be less effective than topical corticosteroid, topical calcipotriene, and topical calcitriol therapy.
Ultraviolet light — Exposure to ultraviolet light is another way to treat psoriasis. During the summer months, people with psoriasis often notice that their symptoms improve. Ultraviolet light treatment (from a dermatologist) may be recommended to treat psoriasis. However, it is important to discuss the potential risks and benefits of ultraviolet light therapy before beginning treatment.
Before receiving ultraviolet light therapy, you may be asked to bathe and gently scrub areas affected by psoriasis, and then apply mineral oil to these areas; the oil allows the light to penetrate the skin more easily.
Although ultraviolet light therapy is effective for treating psoriasis, office treatment can be inconvenient and expensive, despite insurance coverage. Some dermatologists may recommend brief sun exposure or home light treatment (or use of a tanning bed if other options are not feasible) as alternatives to office treatment. Sometimes, an oral medication may be prescribed to sensitize the skin to the light treatment; when this is done, care must be taken to prevent severe burns from occurring.
Risks — Long-term ultraviolet light therapy may increase the risk for skin cancer. Ultraviolet light therapy is not recommended for people with a history of melanoma or other skin cancers. (See "Patient information: Melanoma treatment; localized melanoma (Beyond the Basics)".)
Some clinicians also use lasers to treat psoriasis. The laser allows higher doses of ultraviolet B (UVB) radiation to be directed to the lesions while sparing normal skin; as a result, skin may heal with fewer treatments than with traditional ultraviolet light therapy. Laser treatment is most suitable for people who have small areas of psoriasis.
Methotrexate — Methotrexate treats psoriasis by suppressing the immune response that triggers the disease. This drug is often used to treat moderate to severe psoriasis and/or psoriatic arthritis. It is usually taken once per week, and it may be taken in oral (pill) form or as an injection.
Methotrexate can be used for long-term treatment of psoriasis, although it is important to have your liver monitored during treatment; methotrexate can affect liver function in some people. Patients should avoid drinking alcohol while on methotrexate because alcohol also hurts the liver. Improvement in psoriasis may not be seen until three months of methotrexate treatment are completed.
While taking methotrexate, many providers recommend taking folic acid 1 mg daily or folinic acid 5 mg weekly to reduce the risk of certain methotrexate side effects, such as upset stomach and a sore mouth.
Severe side effects can occur with methotrexate – including damage to the lungs, liver and bone marrow, and even death – so careful monitoring is essential. Serious interactions may occur with certain medications, particularly sulfa-type antibiotics. Methotrexate is not safe to take during pregnancy.
Retinoids — Retinoids are derived from vitamin A. An oral form called acitretin (Soriatane) may be recommended to people with severe forms of psoriasis. Improvement may be noticeable within one month, although the full effect of retinoids may take up to three to six months.
Side effects of retinoids include cracking and drying of the lips and skin, nosebleeds, trouble seeing in the dark, hair loss, joint pain, and depression. Acitretin may cause increased levels of triglycerides and liver enzymes in the blood; blood testing is usually recommended to monitor for these changes. Acitretin can cause severe birth defects and is only slowly removed from the body, so this medication is not used in women of child-bearing potential.
Other immunosuppressive drugs — Several medications that suppress the immune system can be used to treat severe psoriasis for a short period of time. These include cyclosporine, hydroxyurea, and azathioprine.
Injectable medications — Several injectable medications, known as "biologics", target the immune system and may be beneficial in the treatment of psoriasis. Medications include etanercept (Enbrel), infliximab (Remicade), adalimumab (Humira), and ustekinumab (Stelara).
Biologics can be highly effective for the treatment of psoriasis and psoriatic arthritis, with improvement in skin symptoms that usually begins within a few weeks of starting treatment. For patients with psoriatic arthritis, biologics can prevent joint destructions. Because of their cost and potential side effects, biologics are generally reserved for people with moderate to severe psoriasis (or psoriatic arthritis) that has not responded to other treatments.
Etanercept and adalimumab are injected into the skin or muscle by the patient, a family member, or nurse. Etanercept is usually given once or twice a week and adalimumab is usually given every other week. Ustekinumab injections, given every three months, should be given only by trained healthcare providers. Infliximab must be given into a vein over two to three hours. This is typically done in a doctor's office or clinic every eight weeks.
Biologics, like methotrexate and cyclosporine, affect the immune system and should not be used in people with serious infections. Screening for tuberculosis (TB) is necessary before starting therapy since the risk of developing active TB infection is increased. If there is evidence of prior infection with tuberculosis, treatment to prevent reactivation of the infection is recommended (see "Patient information: Tuberculosis (Beyond the Basics)"). Testing for hepatitis B is also recommended.
There may be an increased risk of lymphoma in people who take biologics and other drugs that affect the immune system; more research is needed to define this risk. (See "Overview of biologic agents in the rheumatic diseases".)
WHERE TO GET MORE INFORMATION
Your healthcare provider is the best source of information for questions and concerns related to your medical problem.
This article will be updated as needed on our web site (www.uptodate.com/patients). Related topics for patients, as well as selected articles written for healthcare professionals, are also available. Some of the most relevant are listed below.
Patient level information — UpToDate offers two types of patient education materials.
The Basics — The Basics patient education pieces answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials.
Patient information: Psoriasis (The Basics)
Patient information: Psoriatic arthritis in adults (The Basics)
Patient information: Psoriatic arthritis in children (The Basics)
Beyond the Basics — Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are best for patients who want in-depth information and are comfortable with some medical jargon.
Patient information: Psoriatic arthritis (Beyond the Basics)
Patient information: Melanoma treatment; localized melanoma (Beyond the Basics)
Patient information: Tuberculosis (Beyond the Basics)
Professional level information — Professional level articles are designed to keep doctors and other health professionals up-to-date on the latest medical findings. These articles are thorough, long, and complex, and they contain multiple references to the research on which they are based. Professional level articles are best for people who are comfortable with a lot of medical terminology and who want to read the same materials their doctors are reading.
Approach to the patient with a scalp eruption
Approach to the patient with anal pruritus
Approach to the patient with pustular skin lesions
Clinical manifestations and diagnosis of psoriatic arthritis
Epidemiology, clinical manifestations, and diagnosis of psoriasis
Management of psoriasis in pregnant women
Pathogenesis of psoriatic arthritis
Treatment of psoriasis
Treatment of psoriatic arthritis
Overview of biologic agents in the rheumatic diseases
The following organizations also provide reliable health information.
- National Library of Medicine
- National Institute on Arthritis and Musculoskeletal and Skin Diseases
- American Academy of Dermatology
- American Academy of Allergy, Asthma and Immunology
- National Psoriasis Foundation