A problem with the immune system may play a role, and some people are genetically predisposed to psoriasis.
Characteristic scales or red patches can appear anywhere on the body in large or small patches, particularly the elbows, knees, and scalp.
This disease is treated with a combination of drugs applied to the skin, exposure to ultraviolet light (phototherapy), and drugs taken by mouth or given by injection.
Psoriasis is common and affects about 1 to 5% of the population worldwide. Light-skinned people are at greater risk, whereas Black people are less likely to get the disease. Psoriasis begins most often in people aged 16 to 22 years and aged 57 to 60 years. However, people in all age groups and races are susceptible.
The patches of psoriasis occur because of an abnormally high rate of growth of skin cells. The reason for the rapid cell growth is unknown, but a problem with the immune system is thought to play a role. The disorder often runs in families, and certain genes are associated with psoriasis.
Symptoms of Psoriasis
Plaque psoriasis, the most common type of psoriasis, usually starts as one or more small red, silvery, shiny patches (plaques) on the scalp, elbows, knees, back, or buttocks. The eyebrows, underarms, navel, the skin around the anus, and the cleft where the buttocks meet the lower back may also be affected. Many people with psoriasis may also have deformed, thickened, and pitted nails.
The first patches may clear up after a few months or remain, sometimes growing together to form larger patches. Some people never have more than one or two small patches, and others have patches covering large areas of the body. Thick patches or patches on the palms of the hands, soles of the feet, or skinfolds of the genitals are more likely to itch or hurt, but many times the person has no symptoms. Although the patches do not cause extreme physical discomfort, they are very obvious and often embarrassing to the person. The psychologic distress caused by psoriasis can be severe.
Psoriasis persists throughout life but may come and go. Symptoms of psoriasis are often diminished during the summer when the skin is exposed to bright sunlight. Some people may go for years between occurrences.
About 5 to 30% of people with psoriasis develop arthritis (psoriatic arthritis Psoriatic Arthritis Psoriatic arthritis is a spondyloarthritis and a form of joint inflammation that occurs in some people who have psoriasis of the skin or nails. Joint inflammation can develop in people who have... read more ). Psoriatic arthritis causes joint pain and swelling.
Psoriasis may flare up for no apparent reason or as a result of a variety of circumstances. Flare-ups often result from conditions that irritate the skin, such as minor injuries and severe sunburn Sunburn Sunburn results from a brief (acute) overexposure to ultraviolet (UV) light. Overexposure to ultraviolet light causes sunburn. Sunburn causes painful reddened skin and sometimes blisters, fever... read more . Sometimes flare-ups occur after infections, such as colds and strep throat Throat Infection Infections of the throat and/or tonsils are common, particularly among children. Throat infections are usually caused by a virus but may be caused by bacteria such as streptococcal bacteria... read more . Flare-ups are more common in the winter, after drinking alcohol, and after stressful situations. Many drugs, such as antimalarial drugs, lithium, angiotensin-converting enzyme (ACE) inhibitors, terbinafine, interferon-alpha, and beta-blockers, can also cause psoriasis to flare up. Flare-ups are also more common among people who are obese Obesity Obesity is excess body weight. Obesity is influenced by a combination of factors, which usually results in consuming more calories than the body needs. These factors may include physical inactivity... read more , infected with the human immunodeficiency virus Human Immunodeficiency Virus (HIV) Infection Human immunodeficiency virus (HIV) infection is a viral infection that progressively destroys certain white blood cells and can cause acquired immunodeficiency syndrome (AIDS). HIV is transmitted... read more (HIV), or smoke tobacco.
Uncommon types of psoriasis
Some uncommon types of psoriasis can have more serious effects.
Erythrodermic psoriasis causes all of the skin on the body to become red and scaly. This form of psoriasis is serious because, like a burn, it keeps the skin from serving as a protective barrier against injury and infection.
Pustular psoriasis is another uncommon form of psoriasis. In this form, large and small pus-filled blisters (pustules) are scattered widely on the body.
Palmoplantar psoriasis is a form of pustular psoriasis in which pustules occur primarily on the hands and feet. It is sometimes called palmoplantar psoriasis of the palms and soles.
Diagnosis of Psoriasis
A doctor's evaluation
Sometimes skin biopsy
Doctors base the diagnosis of psoriasis on how the scales and plaques look and where they appear on the body.
Sometimes, doctors take a sample of skin tissue and examine it under a microscope to rule out other disorders (such as skin cancer Overview of Skin Cancer Skin cancer is the most common type of cancer. Skin cancer is most common among people who work or play sports outside and among sunbathers. Fair-skinned people are particularly susceptible... read more ).
Treatment of Psoriasis
Many drugs are available to treat psoriasis. Most often, a combination of drugs is used, depending on the severity and extent of the person's symptoms.
Topical drugs (drugs applied to the skin) are used most commonly. Nearly everyone with psoriasis benefits from skin moisturizers Moisturizing agents (emollients) Topical drugs (drugs applied directly to the skin) are a mainstay of treating skin disorders. Systemic drugs are taken by mouth or given by injection and are distributed throughout the body... read more (emollients).
Other topical agents include corticosteroids Anti-inflammatory agents Topical drugs (drugs applied directly to the skin) are a mainstay of treating skin disorders. Systemic drugs are taken by mouth or given by injection and are distributed throughout the body... read more , often used together with calcipotriene (also called calcipotriol), which is a form of vitamin D, or coal tar.
Tacrolimus and pimecrolimus are used to treat psoriasis that appears on delicate skin (such as on the face or groin or in skinfolds). Tazarotene or anthralin may also be used.
Very thick patches can be thinned with ointments containing salicylic acid, which make the other drugs more effective.
Many of these drugs are irritating to the skin, and doctors must find which ones work best for each person.
Phototherapy (exposure to ultraviolet light) also can help clear up psoriasis for several months at a time ( see Phototherapy: Using Ultraviolet Light to Treat Skin Disorders Phototherapy: Using Ultraviolet Light to Treat Skin Disorders ). Phototherapy is often used in combination with various topical drugs, particularly when large areas of skin are involved. Traditionally, treatment has been with phototherapy combined with the use of psoralens (drugs that make the skin more sensitive to the effects of ultraviolet light). This treatment is called PUVA (psoralen plus ultraviolet A).
Many doctors are now using narrowband ultraviolet B (NBUVB) treatments, which are as effective as PUVA. However, NBUVB treatments are done without psoralens and therefore do not have the same side effects, such as extreme sensitivity to sunlight.
Doctors can also treat specific patches of the skin directly by using a laser that focuses ultraviolet light (called excimer laser therapy).
Immunosuppressants are drugs that intentionally weaken (suppress) the immune system to keep it from making psoriasis worse. These drugs can be taken by mouth or given by injection. Immunosuppressants can reduce the body's ability to fight infections.
Cyclosporine can be used to treat severe psoriasis. This drug may cause high blood pressure and damage the kidneys.
Mycophenolate mofetil commonly causes gastrointestinal problems and bone marrow suppression (decreased production of red blood cells, white blood cells, and platelets). It may also increase the risk of lymphoma and other cancers.
Methotrexate decreases inflammation in the body and interferes with the growth and multiplication of skin cells. Doctors use methotrexate to treat people whose psoriasis is severe or does not respond to less harmful forms of therapy. Liver damage and impaired immunity are possible side effects.
Other drugs may be given to treat serious forms of psoriasis and psoriatic arthritis.
Acitretin is particularly effective in treating pustular psoriasis but often raises fat (lipid) levels in the blood and might cause problems with the liver and bones as well as reversible hair loss. This drug is given by mouth. It can cause severe birth defects and should not be taken by women who may become pregnant. Women should wait at least 2 years after their last dose of acitretin before attempting pregnancy.
Biologic agents are made from living organisms and inhibit certain chemicals involved in the immune system. They include etanercept, adalimumab, infliximab, certolizumab, ustekinumab, secukinumab, brodalumab, ixekizumab, tildrakizumab, risankizumab, guselkumab, and tofacitinib. All of these drugs are given by injection except tofacitinib, which is taken by mouth. Apremilast is another option and it is taken by mouth. These drugs tend to be the most effective drugs for severe psoriasis, but they can have side effects.
The following is an English-language resource that may be useful. Please note that THE MANUAL is not responsible for the content of this resource.
National Psoriasis Foundation: A resource providing information about treatments and community support