What is psoriasis?

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Definition of psoriasis

What exactly is psoriasis? Let's start with what it's not. It is not contagious and it is not just a skin disease. Psoriasis is a chronic inflammatory disease of the immune system. The exact cause is unknown; however, researchers believe that heredity, environment, and the immune system may also play a role in psoriasis.

Normally, skin cells that are formed in the deepest layers of your skin make their way to the surface. They mature, are sloughed off the body's surface, and replaced with new skin cells from below. This cycle takes approximately a month.

In people with psoriasis, however, the immune system is mistakenly activated, resulting in an abnormally rapid skin cell cycle. This means the cells move from the deepest layers of your skin to the surface in about four days. Since they migrate so quickly, they don't have time to properly mature. In the most common type of psoriasis, plaque psoriasis, the cells accumulate on the surface, forming raised, red patches or "lesions."

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Types of psoriasis and where symptoms may occur

While plaque psoriasis is the most common type, psoriasis appears in a variety of forms that can occur on different parts of the body.

Types

• Plaque psoriasis (psoriasis vulgaris) appears as dry, scaly patches of skin and is the most common form of the disease
• Guttate psoriasis emerges as pink to red drop-like lesions which may form a scale
• Inverse psoriasis appears as smooth, red lesions and is found primarily in the armpits, groin, and skin folds
• Pustular psoriasis appears as white, pus-filled blisters
• Erythrodermic psoriasis develops over large areas of the body; skin is red with excess shedding of fine scales

Where symptoms may occur

Psoriasis may occur on any part of the body. Locations which may be overlooked or misunderstood include the hands, feet, scalp and nails.

• Palmo-Plantar is a localized type of psoriasis that appears on hands and feet
• Scalp may appear with red lesions that may form scales
• Nails may appear pitted, thickened, discolored, and loosened from the nail bed

Additionally, if you also experience joint pain, morning stiffness, or fatigue you may have psoriatic arthritis.

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Causes of psoriasis

Over time, our understanding of psoriasis has changed dramatically. Long considered just a skin disease, psoriasis is now recognized as an inflammatory disease of the immune system. Researchers believe that the disease occurs when your immune system (your natural protection against bacteria, viruses, and other foreign invaders) is accidentally activated, resulting in an acceleration of the normal skin cell cycle. This in turn causes an accumulation of skin cells on the surface of the skin.

While no one knows what triggers this response, heredity and environmental factors may also play a role.

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Who gets psoriasis?

If you have psoriasis, you're not alone. Research indicates that up to 7 million people in the United States have psoriasis. It affects men and women at equal rates, affects all age groups, and is most common in people of European ancestry.

Although there are many different types of psoriasis, about 80% of people with psoriasis have the more common type known as plaque psoriasis.