Psoriasis 101

By Kira Mayo

What is psoriasis?

Psoriasis is a chronic inflammatory condition. It appears most commonly as well-circumscribed (meaning that the borders are distinct), red patches covered with silvery scales. The exact cause is unknown, but common triggers include trauma, infection, and certain drugs (such as oral lithium and beta-blockers). Symptoms are usually minimal with occasional itching, but the psychological implications may be major—patients are embarrassed about the appearance of their skin. Some people develop severe disease with painful arthritis. Diagnosis is based on appearance and distribution of the skin findings. Treatment is with topical medications, phototherapy or systemic (oral or injectable) medications.

Who gets psoriasis and how does it form?

Psoriasis affects about 1-5% of the population worldwide. About one third of all cases of psoriasis are inherited, suggesting that there is a genetic component to this condition. Researchers are currently studying affected families to identify genetic factors that can cause the disease.

So why does psoriasis occur? Psoriasis occurs when cells in the outer layer of the skin reproduce faster than normal. This causes the cells to pile up on the skin’s surface, producing thick, red patches that usually itch and may burn.

How can I recognize psoriasis?

Psoriatic patches either itch or are not bothersome at all. They are mainly found on the scalp, elbows and knees. Psoriasis can also affect the fingernails, toenails, and mucous lining of the mouth and genitalia. Lesions of psoriasis differ in appearance depending on the type:

1- Plaque psoriasis is the most common form of psoriasis; the patches are discrete and red and are covered by silvery scales. They appear gradually and remit and recur either on their own or with appearance and resolution of triggers.

2- Guttate psoriasis is characterized by small lesions on the abdomen, chest, back, limbs and scalp; it is sometimes triggered by bacterial infections.

3- Pustular psoriasis is characterized by blisters filled with noninfectious pus. This type of psoriasis can be triggered by medication, infection, emotional stress, or exposure to certain chemicals.

4- Inverse psoriasis is characterized by large, dry, smooth, red plaques in the folds of the skin near the genitals, under the breasts or in the armpits; it is related to increased sensitivity to friction and sweating.

5- Erythrodermic psoriasis is characterized by an extensive red, scaly lesion that is itchy or painful. This type of psoriasis can be triggered by a severe sunburn or certain medications.

How is psoriasis diagnosed?

Doctors usually diagnose psoriasis after a careful examination of the skin. The disease is graded as mild, moderate or severe based on the lesions’ effect on the patient’s ability to manage the disease.

How is psoriasis treated?

Treatment depends on how severe the psoriasis is, how much of the body is affected, the type of psoriasis and how well the skin responds to the initial treatment. A topical treatment, applied directly to the skin, is usually tried first. Phototherapy, treatment with light, is then used if topical therapy doesn’t cut it. The last resort is systemic treatment; patients who have severe psoriasis have to take oral or injectable medications. For more information on treating psoriasis, see Psoriasis Management.


Psoriasis is considered to be a life-long inflammatory condition. Though it can flare up at times, treatment options are available to control it. Several treatments may need to be tried before finding one that works. As we learn more about this condition, more treatment options are becoming available, allowing patients with psoriasis to lead normal, symptom-free lives!

Reference: Psoriasis: Psoriasis and Scaling Diseases. The Merck Manual for Healthcare Professionals, Nov. 2005. Web.

Originally written for


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