Psoriasis begins when certain areas of skin produce new skin cells much more rapidly than normal, causing a thickening and scaling of the skin.

The scaly, red patches of skin caused by psoriasis affect men and women of all ages. They can erupt anywhere on the body, clear up for months at a time, and then reappear.Photograph of psoriasis

Although the exact causes of psoriasis are not known, the immune system is involved and heredity may play a role; at least 1 of 3 people with psoriasis has an immediate relative with the disease.

Psoriasis can be triggered by a strep throat infection, heavy alcohol consumption, stress, some medicines (such as beta blockers and lithium), injury to the skin, and infection with the human immunodeficiency virus (HIV).

Symptoms of psoriasis

Psoriasis appears as reddish patches of skin covered with silvery scales; they may or may not cause discomfort.

There are several types of psoriasis:

  • plaque psoriasis. This is the most common type. Patches appear on the trunk and limbs, especially on the elbows and knees, and on the scalp. Fingernails and toenails may become thick, pitted, and separated from their nail beds.
  • inverse psoriasis. This is a plaque type of psoriasis that tends to affect skin creases. Creases in the underarm, groin, buttocks, genital areas or under the breast are particularly affected. The red patches may be moist rather than scaling.
  • pustular psoriasis. This type is characterized by small pustules spread over the body.
  • guttate psoriasis. This type causes many teardrop-sized patches that are more prominent on the body than on the face. It often develops after a strep throat infection or an upper respiratory tract infection.

Among people with psoriasis, 1 in 7 develop psoriatic arthritis, an autoimmune disease that causes inflammation of the joints.

Diagnosing psoriasis

The typical skin and nail changes of this disorder are often all that are needed to make a diagnosis. When skin symptoms aren't typical, your doctor may recommend that you have a skin biopsy, in which a small sample of skin is removed and examined in a laboratory. The biopsy can confirm the diagnosis and rule out other possible skin disorders.

Treating psoriasis

Psoriasis is a chronic condition for which there is no cure. However, there are many treatments available to help keep it from getting worse, or flaring up. Treatment depends on the type, its location, and how widespread it is.

Topical treatments

These are treatments applied directly to the skin. They include:

  • daily skin care with lubricants such as petroleum jelly or unscented moisturizers
  • corticosteroid creams, lotions, and ointments rubbed onto plaques on the hands, feet, arms, legs and trunk, face, and elsewhere. Low-strength versions are available over the counter. Stronger versions are by prescription only.
  • calcipotriol (Dovonex) slows production of skin scales
  • tazarotene (Tazorac) is a synthetic vitamin A derivative
  • coal tar
  • salicylic acid can be used to remove scales


Extensive or widespread psoriasis may be treated with light (phototherapy). A treatment called PUVA combines ultraviolet A light treatment with an oral medication that improves the effectiveness of the light treatment.

Laser treatment also can be used. It allows treatment to be more focused so higher amounts of UV light can be used.

Vitamin A derivatives

These are used to treat moderate to severe psoriasis involving large areas of the body. These treatments are very powerful. Some have the potential to cause severe side effects, so it is essential to understand the risks and be monitored closely.


These drugs work by suppressing the immune system. They are used to treat moderate to severe psoriasis involving large areas of the body.

Antineoplastic agents

Anticancer drugs like methotrexate are sometimes used to treat severe psoriasis.

Biologic therapies

Biologic drugs, or biologics, target specific parts of the immune system. They block the action of a specific type of immune cell called a T cell, or block proteins in the immune system, such as tumor necrosis factor-alpha (TNF-alpha) or inflammatory proteins known as interleukin-12 and interleukin-23. These cells and proteins all play a major role in developing psoriasis and psoriatic arthritis.

Biologics are given by injection or intravenous infusion. They include

  • etanercept (Enbrel), adalimumab (Humira), infliximab (Remicade), and golimumab (Simponi), all of which block TNF-alpha.
  • ustekinumab (Stelara) targets interleukin-12 and interleukin-23, both of which are associated with psoriasis-related inflammation


As a service to our readers, Harvard Health Publishing provides access to our library of archived content. Please note the date of last review or update on all articles.

No content on this site, regardless of date, should ever be used as a substitute for direct medical advice from your doctor or other qualified clinician.

Free Healthbeat Signup

Get the latest in health news delivered to your inbox!

Sign Up
Harvard Health Publishing Logo

Thanks for visiting. Don't miss your FREE gift.

The Best Diets for Cognitive Fitness, is yours absolutely FREE when you sign up to receive Health Alerts from Harvard Medical School

Sign up to get tips for living a healthy lifestyle, with ways to fight inflammation and improve cognitive health, plus the latest advances in preventative medicine, diet and exercise, pain relief, blood pressure and cholesterol management, and more.

Harvard Health Publishing Logo

Health Alerts from Harvard Medical School

Get helpful tips and guidance for everything from fighting inflammation to finding the best diets for weight loss...from exercises to build a stronger core to advice on treating cataracts. PLUS, the latest news on medical advances and breakthroughs from Harvard Medical School experts.

BONUS! Sign up now and
get a FREE copy of the
Best Diets for Cognitive Fitness

Harvard Health Publishing Logo

Stay on top of latest health news from Harvard Medical School.

Plus, get a FREE copy of the Best Diets for Cognitive Fitness.