- Related Topics:
- skin disease
- psoriatic arthritis
- PUVA therapy
- familial disease
- On the Web:
- National Center for Biotechnology Information - Psoriasis (Oct. 25, 2026)
psoriasis
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What is psoriasis?
Psoriasis is a chronic, recurring, inflammatory skin condition characterized by raised, scaly plaques, often on the elbows, knees, scalp, chest, and buttocks. It is an autoimmune disorder where T cells attack healthy skin cells, causing cells to reproduce faster than normal and shortening their life span to 3 to 5 days.
Psoriasis affects about 2–3% of the U.S. population and is more common in northern climates. Its onset can be gradual or sudden, triggered by skin injuries, infections, or psychological stress. Sunlight may reduce the severity of lesions. Though there is no cure, treatments like topical creams, phototherapy, and oral medications can help relieve symptoms.
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What are the main symptoms of psoriasis?
Psoriasis, a chronic inflammatory skin disorder, has several characteristic symptoms. The most common type, plaque psoriasis, is marked by reddish, slightly raised patches or papules covered with silvery-white scales. These lesions often appear symmetrically on the elbows, knees, scalp, chest, and buttocks.
Other symptoms and signs include:
* Thickened, brittle, and irregularly laminated nails
* Possible itching
* Psoriatic arthritis in some individuals, affecting joints and the spine
* Small areas of neutrophil leukocytes in the epidermis4 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
How does psoriasis affect the skin?
Psoriasis is a chronic, recurring inflammatory skin condition where the immune system mistakenly attacks healthy skin cells, causing the skin cell life cycle to shorten from about 20 to 28 days to just 3 to 5 days. This rapid reproduction of skin cells leads to raised, scaly plaques, especially on the knees, elbows, buttocks, and knuckles. These lesions can be small or merge into larger geometrical patterns, and nails may thicken and become brittle. The accelerated proliferation of keratinocytes, the predominant cell type in the epidermis, is a key feature of psoriasis. Although psoriasis isn't contagious, it can be disfiguring.
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How does the immune system play a role in psoriasis?
Psoriasis is an immune-mediated disorder where T cells attack healthy skin cells, causing the skin cells' life span to shorten to 3 to 5 days, which normally live for 20 to 28 days. This immune response results in the rapid reproduction of skin cells, leading to raised, scaly plaques, especially on the knees, elbows, buttocks, and knuckles.
Neutrophil leukocytes accumulate in the epidermis, forming microabscesses. Leukotrienes and complement fragments may mediate this process. The skin's blood vessels also exhibit increased twisting.
Treatments include topical applications, phototherapy, and oral medications that suppress the immune system or modulate it by attacking improperly working immune cells.
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What are some possible complications or long-term effects of psoriasis on the body?
Psoriasis is a chronic inflammatory skin disorder that can lead to several complications and long-term effects on the body. About 10% to 30% of individuals with psoriasis may develop psoriatic arthritis, a specific type of arthritis that can affect the joints in the fingers and spine. In severe cases of psoriatic arthritis, a rare pattern known as arthritis mutilans can occur, leading to bone destruction and telescoping of the fingers or toes.
In addition, long-term phototherapy treatments, which involve exposing the skin to ultraviolet light, can increase the risk of skin cancer. Severe complications of psoriasis also include extensive sloughing of the outer layer of the skin, resulting in inflammation.
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psoriasis, a chronic, recurrent inflammatory skin disorder. The most common type, called plaque psoriasis (psoriasis vulgaris), is characterized by slightly elevated reddish patches or papules (solid elevations) covered with silvery white scales. In most cases, the lesions tend to be symmetrically distributed on the elbows and knees, scalp, chest, and buttocks. The lesions may remain small and solitary or coalesce into large plaques that often form geometrical patterns with a central area of normal skin. In many cases the nails become thickened, irregularly laminated, and brittle. In addition to plaque psoriasis, there are four other types of psoriasis, including guttate, pustular, inverse (or flexular), and erythrodermic.
Psoriasis is an immune-mediated (or autoimmune) disorder that occurs when immune cells known as T lymphocytes, or T cells, attack healthy skin cells in both the nonvascular horny outer layer of the skin and its deeper vascular layer. This attack causes the life span of the skin cells to shorten to about 3 to 5 days (skin cells normally live about 20 to 28 days) and forces the cells to reproduce more rapidly than normal. Psoriasis occurs in both sexes with equal frequency, being most prevalent between the ages of 10 and 30. It is most often seen in northern climates. An estimated 2 to 3 percent of the U.S. population is affected by psoriasis. In contrast, between 0.05 and 0.3 percent of Asians experience the condition. In European countries the incidence of psoriasis is highly variable, affecting anywhere from less than 1 percent to more than 6 percent of populations.
The onset of psoriasis is usually gradual but occasionally explosive. Precipitating factors may include injury to the skin, acute infection, and psychological upsets. Ordinarily, the lesions become less severe and sometimes disappear during the summer, possibly owing to the effect of sunlight. The severe complications of psoriasis are extensive sloughing of the outer layer of the skin, with resulting inflammation, and psoriatic arthritis. Generally, however, individuals with psoriasis are in relatively good health. The variability in the progression and severity of the disorder has led researchers to suspect that the underlying causes of psoriasis are the result of complex interactions between genetic and environmental factors.
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There is no permanent cure for psoriasis, but there are a variety of treatments aimed at relieving the associated skin symptoms. Topical treatments for psoriasis come in different forms (e.g., creams and gels) and generally provide relief from inflammation and scaling. Some, such as retinoids (derivatives of vitamin A) and synthetic forms of vitamin D, work by slowing skin cell reproduction, whereas others, such as corticosteroids, coal-tar ointment, and salicylic acid, work by reducing inflammation. Psoriasis can also be treated with phototherapy, in which the skin is exposed to ultraviolet light. While phototherapy can be highly effective, it does have side effects, including pain, irregular pigmentation, and scarring. In addition, long-term treatments are associated with an increased risk of skin cancer.
Oral medications are available to treat psoriasis but are often used as a last resort, because the drugs that are most effective in treating psoriasis suppress the immune system, making patients susceptible to a multitude of infections and illnesses that can be life-threatening. Oral drugs that are used to reduce inflammation include methotrexate, cyclosporine, and azathioprine. Oral drugs called biologics (because they are made from human or animal proteins) modulate the immune system by attacking immune cells that are working improperly. Several biologics have been approved for psoriasis, including infliximab (Remicade), etanercept (Enbrel), and guselkumab (Tremfya).