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Last Updated: Mar 1, 2019


Psoriasis is a chronic inflammatory disorder of the skin, in which the skin produces new skin cells too quickly. Normally, in a process called turnover, the lowest level of the epidermis produces new skin cells that rise to the outermost layer of the skin in a period of one month. In psoriasis, rapid turnover occurs in only a few days. In the most common forms of psoriasis, excess skin cells accumulate on the skin surface, resulting in thick patches (plaques) of reddened, inflamed skin covered with silvery white scales.

This disease usually develops in individuals between the ages of 15 to 30 years. Psoriasis is a life-long condition, erupting at unpredictable intervals, alternating with periods of remission.

Causes and Risk Factors

patient with psoriasis on back and arms

The underlying cause of psoriasis is unknown. However, research has established that psoriasis is the result of a malfunction of the immune system, in which certain white blood cells (termed T cells) mistakenly attack the skin, triggering inflammation and rapid skin cell turnover.

Risk factors for the development of psoriasis include the following:

  • Genetics (psoriasis often runs in families)
  • Streptococcal throat infection
  • Skin injury
  • Stress
  • Certain medications
  • Smoking
  • Obesity.


Individuals with psoriasis usually develop raised red plaques with silvery white scales, associated with itching and pain. Reddened skin beneath the plaques easily bleeds when the scales are removed. Plaques can range from tiny spots to extensive eruptions across large areas.

Typically, psoriasis erupts symmetrically, but unilateral symptoms can occur. Affected areas usually include the extensor surface of the elbows, knees, scalp, lower back, buttocks and genital area. Commonly, nails appear thickened, pitted and deformed.

Symptoms are characterized by cycles of worsening (flares) for weeks or months followed by periods of improvement or even complete remission. Additionally, individuals with psoriasis frequently feel self-conscious about the appearance of their skin, which can result in social isolation and depression.

Characteristics of the Major Types of Psoriasis

Chronic Plaque Psoriasis:

  • Most common form of psoriasis
  • Raised, red plaques with silvery, scaly surface.

Guttate Psoriasis:

  • Typically small sores on the trunk, extremities and scalp
  • Frequently precipitated by a streptococcal bacteria throat infection
  • Often self-limiting, resolving without treatment in 6-12 weeks.

Scalp Psoriasis:

  • Red, scaly patches on the scalp
  • Commonly spreads past the hairline.

Inverse Psoriasis:

  • Well-demarcated areas of redness, but scaliness is absent
  • Affects skin folds such as under the breasts, axilla, genital area and neck
  • Obesity is a major risk factor.

Pustular Psoriasis:

  • Pustules (blisters filled with pus) on the trunk and extremities
  • Fever
  • Dehydration
  • Often life-threatening
  • Difficult to control and requires aggressive treatment.

Erythrodermic Psoriasis:

  • Least common form of psoriasis
  • Red rash with scales, burning and itching across the entire body
  • Often severe and difficult to control.

Psoriatic Arthritis:

  • Red, inflamed, scaly skin
  • Nail pitting
  • Swollen joints.
psoriasis plaques

Diagnosis and Treatment

Most cases of psoriasis are diagnosed by the patient’s symptoms and physical examination. Rarely, a skin biopsy is necessary to rule out other conditions that may resemble psoriasis.

There is no cure for psoriasis; therefore, the main goal of treatment is to slow the rapid turnover of skin cells and relieve symptoms.

Topical Treatment

In treating psoriasis, medications are applied directly to the surface of the skin.

  • Topical corticosteroids decrease inflammation; suppress the immune system; slow skin turnover; and decrease itching.
  • Vitamin D analogs, synthetic compounds based on naturally occurring vitamin D, help decrease skin cell growth.
  • Retinoids, synthetic compounds derived from vitamin A, normalize skin cell activity and decrease inflammation.
  • Coal tar decreases scaling and inflammation.
  • Anthralin decreases inflammation and skin cell turnover; diminishes scaliness; and smoothes the skin.
  • Salicylic acid peels the skin and reduces scaliness.

Light Therapy


  • A natural form of ultraviolet light.
  • Brief exposure reduces T cell activity and decreases scaliness.
  • Prolonged exposure causes skin damage.

Ultraviolet B (UVB) Phototherapy:

  • A short wave ultraviolet light provided by an artificial light source.
  • Useful for mild to moderate cases of psoriasis.
  • Risks include burning the epidermis.

Narrowband UVB Therapy:

  • A newer and more effective form of UVB therapy.
  • Carries a higher risk of burns.

Goeckerman Therapy:

  • A combination of coal tar and UVB treatment.
  • Coal tar makes UVB treatment more effective.

Psoralen and Ultraviolet A (UVA) Phototherapy (PUVA):

  • A combination of a drug called psoralen and UVA light therapy.
  • UVA is a long wave ultraviolet light that penetrates deep into the dermis.
  • Psoralen makes skin more sensitive to UVA rays.
  • Only used for severe cases of psoriasis.
  • Increases risk for sunburns, premature aging and skin cancer.

Excimer Laser:

  • A form of UVB light therapy.
  • Directed only at the affected skin so normal skin is not harmed.

Systemic Treatment

In the case of these treatment methods, medications are administered orally or by injection for severe cases of psoriasis.


  • Suppresses the immune system and decreases the growth of skin cells.
  • Increases the risk for liver damage and impairs the body’s ability to fight infection.


  • Reduce the production of skin cells.
  • Increase the risk of birth defects and are not to be used during pregnancy.


  • Suppresses the immune system to decrease skin cell turnover.
  • Increases the risk of infection and cancer.

Biologic response modifiers (biologics):

  • Proteins derived from natural sources that suppress the immune system.
  • Increase the risk of infection and cancer.


There are no known preventative measures for psoriasis and genetics is a major risk factor for this disease. However, individuals may decrease their risk by avoiding other factors such as smoking, stress and obesity.


  • Gudjonsson JE, Elder JT. Chapter 18. Psoriasis. In: Goldsmith LA, Katz SI, Gilchrest BA, Paller AS, Leffell DJ, Wolff K. eds. Fitzpatrick’s Dermatology in General Medicine, 8e. New York, NY: McGraw-Hill; 2012.
  • Questions and Answers about Psoriasis. National Institute of Arthritis and Musculoskeletal and Skin Diseases website. Accessed October 13, 2014.
  • Psoriasis. Mayo Clinic website. Accessed October 13, 2014.

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Tina Shahian, PhD

Tina is a writer for Innerbody Research, where she has written a large body of informative guides about health conditions.


A communication specialist in life science and biotech subjects, Tina’s successful career is rooted in her ability to convey complex scientific topics to diverse audiences. Tina earned her PhD in Biochemistry from the University of California, San Francisco and her BS degree in Cell Biology from U.C. Davis. Tina Shahian’s Linkedin profile.


In her spare time, Tina enjoys drawing science-related cartoons.