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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:


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:

Guttate Psoriasis:

Scalp Psoriasis:

Inverse Psoriasis:

Pustular Psoriasis:

Erythrodermic Psoriasis:

Psoriatic Arthritis:

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.

Light Therapy


Ultraviolet B (UVB) Phototherapy:

Narrowband UVB Therapy:

Goeckerman Therapy:

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

Excimer Laser:

Systemic Treatment

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




Biologic response modifiers (biologics):


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.


Additional Resources

Home Health Testing Guides

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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.