Causes and Risk Factors of Psoriasis

Psoriasis was once thought to be a dermatological condition like eczema but is, in fact, an autoimmune disorder more closely related to rheumatoid arthritis and lupus. Per its name, an autoimmune disorder is one in which the body's immune system turns its defenses on itself, attacking cells and tissues it mistakenly thinks are harmful. With psoriasis, the primary target of the assault is cells in the outer layer of skin known as the epidermis, which leads to the formation of dry, red, scaly patches called plaques.

Researchers don't fully understand what causes the immune system to malfunction in this way but believe that genetics and environmental factors both play a part.

Inflammation

Psoriasis is characterized by inflammation. Inflammation is a factor in many conditions and, in general, starts when a type of white blood cell (T-cell) detects a disease-causing microorganism (pathogen) somewhere in the body. In response, the T-cell moves to the affected tissue and releases an inflammatory protein known as tumor necrosis factor (TNF).

With psoriasis, there is no pathogen. Instead, the T-cells suddenly and inexplicably migrate to the epidermis and secrete TNF as if the body is under attack. The ensuing inflammation is believed to stimulate the hyperproduction of skin cells, known as keratinocytes, which make up around 90% of the epidermis.

The accelerated production causes cells to literally push through the protective outer layer the epidermis, called the stratum corneum, leading to the formation of dry, scaly plaques. Other less common forms of the disease trigger the development of pus-filled blisters (pustular psoriasis) or moist lesions in folds of skin (inverse psoriasis).

Genetics

Genetics is believed to play a central role in the development of psoriasis. While the exact link has yet to be established, scientists have identified no less than 25 genetic mutations that increase a person's risk of the disease.

Among them, a mutation known as CARD14 is believed to be strongly linked to both plaque and pustular psoriasis, as well as a related disorder known as psoriatic arthritis.

The impact of genetics is further evidenced by twins studies in which psoriasis is three times more likely to affect both identical twins than both non-identical twins.

Risk Factors

Although genetics may predispose you to psoriasis, it is possible to have a mutation—even the CARD14 mutation—and never get psoriasis. In order for the disease to develop, scientists believe that an environmental trigger is needed to activate the disease.

This is evidenced, in part, by a variety of conditions that are known to trigger an acute episode (known as a flare). These include, among other things, infections, skin trauma, obesity, and medications.

Infections

Any type of infection can cause psoriasis to appear or flare. This is especially true with guttate psoriasis which almost always follows an infection, most especially a strep infection. Guttate psoriasis is the second most common type of psoriasis and one that strikes children more frequently than adults.

HIV is another infection commonly associated with psoriasis. While people with HIV don't have psoriasis any more often than people in the general population, the severity of the disease tends to be far worse. This isn't surprising given that HIV further suppresses an immune system that is already malfunctioning.

Skin Trauma

Any sort of trauma to the skin (including a cut, scrape, surgical wound, tattoo, burn, or sunburn) can potentially cause a flare. This is known as the Koebner phenomenon, a reaction that occurs along a line of a skin trauma.

Scientists don't totally understand why this occurs but suspect that inflammatory proteins (cytokines) overstimulate the skin and activate autoimmune antibodies (autoantibodies) that incite an inflammatory response.

If you have psoriasis, it is extra important to treat minor skin injuries right away. Clean the skin with soap and water, apply an antibiotic ointment, and cover the wound with a bandage. A compression bandage may be especially useful. Doing so may reduce the risk of an acute flare.

Obesity

A 2017 study from Poland suggests that obesity is a significant risk factor for psoriasis. It is known that the excessive accumulation of adipose (fat-storing) cells stimulations the production of cytokines. This response is closely linked to increases in a person's body mass index (BMI).

It is believed that, at some point, the inflammation induced by obesity can instigate the outbreak of psoriasis symptoms. This often presents in the form of inverse psoriasis, the type that develops in skin folds (including the armpits, under the breasts, between the buttocks, or in the creases of the groin or belly). These are not only the areas with the greatest accumulation of adipose cells but also where the skin is most likely to rub together, causing friction.

Medications

Certain medications can also trigger psoriasis symptoms. It is unclear why this occurs and why some people are affected and others aren't. Among some of the common culprits are:

• High blood pressure medications, including beta-blockers and ACE inhibitors
• Lithium, prescribed to treat bipolar disorders
• Certain disease-modifying antirheumatic drugs (DMARDs), like Plaquenil (hydroxychloroquine) and Aralen (chloroquine)
• Interferons, often used to treat hepatitis C 
• Nonsteroidal anti-inflammatory drugs (NSAIDs)
• Terbinafine, an antifungal drug
• Tetracycline antibiotics

Tumor necrosis factor-a (TNF-a) inhibitors used to treat autoimmune disorders—including Remicade (infliximab), Humira (adalimumab), and Enbrel (etanercept)—can also trigger psoriasis symptoms in the first couple of months of treatment as the body adapts to the medication.

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Lifestyle and Environment

How (and even where) you live can play a role in your risk of psoriasis and your ability to manage the disease.

Smoking

Given how harmful cigarettes are to your general health, it is no surprise that they can also increase your risk of psoriasis. In fact, research published in the journal Psoriasis suggests that the amount you smoke per day is directly linked to your risk for new or recurrent symptoms.

Smoking can also influence your response to treatment by promoting systemic inflammation, reducing the efficacy of anti-inflammatory drugs.

Stress

Stress has an enormous impact on your immune system and can play a significant role in the development of psoriasis. On the flip side, acute psoriatic flares can induce stress and make your condition worse. For some people, stress both triggers and perpetuates the disease.

Even though stress is not entirely avoidable, there are things you can do to control it, including regular exercise, yoga, meditation, and deep breathing.

Physical stress—from surgery or childbirth, for example—is also a common trigger for psoriasis outbreaks.

Cold Weather

People with psoriasis often experience flares during the winter months or when they visit a cold, dry climate.

Cold temperatures sap the air of moisture, leading to dry skin. Winter is also associated with less sunlight, which deprives the body of ultraviolet (UV) radiation beneficial to psoriatic skin. Phototherapy delivered in a dermatologist's office can help counter this effect.

With that being said, too much sun can cause inflammation and sunburn, triggering psoriasis symptoms. The same applies to the use of tanning beds or tanning lamps, both of which should be avoided.

Gluten

Research from the University of California, San Francisco reports that certain people with psoriasis have high levels of gluten antibodies associated with the autoimmune disorder celiac disease (CD). This suggests that gluten, a protein found in some grains, may trigger psoriasis in the same way that it triggers CD.

There is even evidence that a gluten-free diet may improve symptoms in people resistant to traditional psoriasis treatments. Many such individuals may have undiagnosed CD or non-celiac gluten sensitivity.

More research on this potential connection is needed, however.