What causes psoriasis?

by Heather Brannon

Psoriasis is a chronic skin disorder that affects 1% to 3 % of the world's population. It is characterized by periodic flare-ups of well defined red patches covered by a silvery, flaky scale on the extensor surfaces and the scalp. There are several variations of psoriasis but the most common type is chronic plaque psoriasis. The exact cause of psoriasis is unknown, but it is believed that a combination of several factors contribute to the development of this disease.

Immune System Causes of Psoriasis

In a normally functioning immune system, white blood cells produce antibodies to foreign invaders such as bacteria and viruses. These white blood cells also produce chemicals that aid in healing and fighting infective agents. In psoriasis, however, some white blood cells cause the body to fight normal tissue in the skin and, sometimes, joints.

These white blood cells also produce an abnormally large amount of "healing" chemicals that actually cause more inflammation in the skin and joints.

Genetic Causes of Psoriasis

Researchers have now found 4 key genes that are involved with psoriasis. These genes regulate the human leukocyte antigen (HLA) system. The HLA molecules are designed to present foreign substances to the immune system so they can be destroyed, but this process is malfunctioning in psoriasis. Psoriasis patients with a specific HLA genetic factor called HLA-CW6 have a tendency to develop psoriasis at an earlier age. However, only 10% of people who harbor these genes develop psoriasis. Therefore, other factors are required to trigger the disease.

Weather Triggers of Psoriasis

Weather is a strong factor in psoriasis. Cold, dry weather commonly starts a psoriasis flare-up, and hot, damp, sunny weather makes psoriasis symptoms better.

Stress Triggers of Psoriasis

Stress, unexpressed anger, and emotional disorders such as depression and anxiety are strongly associated with psoriasis flare-ups. In one study, nearly 40% of patients remembered a stressful event that occurred within a month of a psoriasis flare. Another study showed that stress can trigger certain immune factors associated with psoriasis.

Infection Triggers of Psoriasis

Infections caused by bacteria or viruses can cause a psoriasis flare. The bacteria streptococcus that causes infections such as tonsillitis, sinusitis, and "strep throat" are a well known trigger of a type of psoriasis called guttate psoriasis. The human immunodeficiency virus (HIV) is also associated with psoriasis.

Skin Injury Triggers of Psoriasis

Sometimes even mild injuries to the skin such as abrasions can trigger a psoriasis flare. This is called the koebner phenomenon, and may be the reason that psoriasis tends to frequently affect the elbows and knees.

Drug Triggers of Psoriasis

The following drugs are known to either worsen psoriasis or induce a flare-up:

Chloroquine
ACE inhibitors such as monopril or captopril
Beta blockers such as lopressor or atenolol
Progesterone
Lithium
Indocin

Psoriasis is the growth of too many skin cells, a normal skin cell matures in 28-30 days but a psoriatic skin cell takes only 3-6 days. The exact cause of this is not known. The actual cause is thought to be genetic in nature and certain events seem to trigger psoriasis such as infections or stressful accidents.

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