What Causes Psoriasis?

Psoriasis is an autoimmune skin condition that occurs because the immune system malfunctions and starts attacking skin cells, causing them to multiply faster than normal.

Genetics and environmental factors, such as chronic stress, certain medicines, infections, smoking, and skin injuries, contribute to psoriasis. The same environmental factors can also trigger disease flare-ups—periods of high disease activity and increased skin symptoms. 

According to the National Psoriasis Foundation, psoriasis affects around 8 million Americans. It affects adults and children alike and occurs equally among people of any sex.

This article will cover the immune system's role in psoriasis, genetic risk, risk factors and triggers, and more. 

Psoriasis and the Immune System

Psoriasis is a type of psoriatic disease—one of two specific inflammatory conditions that affect the joints and skin throughout the body. The other type of psoriatic disease is psoriatic arthritis (PsA). 

Psoriasis primarily affects the skin, but it can sometimes lead to PsA. According to the National Psoriasis Foundation, up to 30% of people with psoriasis will eventually develop PsA. For most, PsA symptoms start about 10 years after psoriasis symptoms begin, but it is possible to develop PsA first or without ever having psoriasis. 

Both types of psoriatic disease are immune system–directed conditions characterized by systemic (whole-body) inflammation. In people with psoriatic disease, the immune system is triggered and starts behaving as if harmful substances have attacked it.

It fights back by causing inflammation, which is the body's natural defense against germs, bacteria, viruses, and other pathogens. But with psoriatic disease, the invaders do not actually exist.

Inflammation presents as skin and joint swelling. In psoriasis, inflammation leads to the overgrowth of skin cells at an accelerated rate that builds up as skin patches called plaques. 

The inflammatory response in psoriatic disease can also cause inflammation that cannot be seen. It will affect other organs and body systems, causing comorbidities (two or more diseases in one person).

Research shows that up to 73% of people with psoriasis have at least one comorbidity. Comorbidities linked to psoriatic disease include heart disease, high blood pressure, diabetes, metabolic syndrome (a combination of conditions that include high blood pressure, high cholesterol, and excess abdominal fat that can lead to stroke, heart disease, and diabetes), anxiety, and depression. 

Is Psoriasis Genetic?

Genetic factors play a key role in the development of psoriasis. But whether someone with genetic risk factors goes on to develop psoriasis depends on environmental triggers and genes working together.

Researchers have identified genes they believe are linked to the development of psoriasis. These include HLA-C, CCHCR1, CDSN, and CARD14.

The research on CARD14 shows this gene produces a large amount of CARD14 protein in skin tissue. CARD14 protein is typically responsible for activating other proteins, including ones that control the body's immune and inflammatory responses.

It's also possible to pass on genes related to the development of psoriasis to a child. But simply having genetic mutations related to the condition does not mean you will go on to develop psoriasis.

Risk Factors and Triggers

Various triggering events can cause psoriasis in people genetically predisposed to it. But the genetics of psoriasis is complex, and healthcare providers can't predict who might develop the condition even when they have a family history.

Triggering events cause a change in the immune system resulting in the condition. Such events include stress, medications, infections, and smoking. 

Stress

Mental stress is a well-established risk factor for psoriasis. It occurs when your life demands exceed your ability to cope.

According to a 2017 British Journal of Dermatology systematic review and meta-analysis of 39 studies, 46% of study participants believed their psoriasis was stress reactive, and 54% recalled stressful preceding events.

Mechanical stress might also trigger psoriasis. This type of stress occurs in the body tissues and is believed to be responsible for different musculoskeletal conditions. A 2019 Journal of Investigative Dermatology report finds that mechanical stress can amplify skin cell and inflammatory protein production.

Medications

Drug-related psoriasis is a recognized trigger for the onset of psoriasis and flare-ups (periods of worsening disease activity). Medication-induced psoriasis has been linked to different prescription drugs, including beta-blockers, lithium, antimalarial drugs, interferons, and tetracycline. 

Researchers do not have any real answers to why some people develop psoriasis from using certain medicines. However, they suspect some drugs might affect skin cell production and trigger inflammatory processes.

Infections

Strep throat and staph infections are commonly linked to the development of psoriasis. Some kinds of yeast infections might also be linked to psoriasis.

The connection between strep throat and psoriasis is well-established, especially guttate psoriasis, which appears as small, round spots. Strep infections can also lead to other types of psoriasis. 

A staph infection is caused by Staphylococcus bacteria that can either lead to a minor or life-threatening skin infection. Colonization of staph bacteria in psoriasis lesions has been found in up to 60% of people with the condition compared to 5% to 30% of normal healthy skin. Staph bacteria are also linked to more severe psoriatic disease.

Smoking

Smoking increases the risk of psoriasis in people genetically disposed to the condition. It might also worsen symptoms and reduce treatment response.

Quitting smoking reduces your risk for psoriasis and other inflammatory diseases. A healthcare provider can offer resources and advise you on the best ways to quit.

Alcohol

Like smoking, alcohol can put you at risk for psoriasis and other inflammatory diseases. Alcohol might trigger inflammation and worsen symptoms for some people with psoriasis. Alcohol also can reduce the effectiveness of certain medications or lead to severe drug side effects.

Obesity

Having obesity, defined as a body mass index (BMI) of over 30, is a risk factor for the development of psoriasis. Being overweight could also mean worsening symptoms, and psoriasis can lead to weight gain.

The reason for the increased risk is that fat tissues release adipokines—a type of inflammatory cytokine (chemical messenger that regulates the inflammatory response). The more body fat there is, the more adipokines that get released.

Weight loss in people with excess fat appears to improve psoriasis symptoms. Weight loss might also improve the response to oral systemic therapies (medications taken by mouth that work throughout the body), including biologics. 

Weather

It is unknown if weather increases psoriasis risk. But cold, dry weather might trigger a psoriasis flare for some people.

A study reported in 2015 in the Journal of the American Academy of Dermatology found that many people with psoriasis report clearer skin during the summer months. In contrast, most experienced moderate to severe symptoms in the winter months.

Skin Injury

Psoriasis can occur in areas where there is damage to the skin. A skin injury could be anything from an injection to a sunburn to a deep cut to a tattoo. This is called the Koebner phenomenon (skin lesions that appear due to trauma in previously health skin). It causes psoriasis lesions days or weeks after a skin injury.

Is Psoriasis Contagious?

Psoriasis is not a contagious condition. It is a problem with the immune system, in which it malfunctions and tries to fight harmful pathogens that do not exist.

Because psoriasis is an immune system problem, it cannot be acquired from skin-to-skin contact with someone with the condition. You cannot get it from hugging, kissing, having sex, or being near someone who has psoriasis lesions.

Summary 

Psoriasis is an autoimmune skin conditon that occurs when the immune system malfunctions and starts to attack healthy tissues. Those attacks lead to inflammation which causes skin cells to grow too quickly, forming skin patches. 

Genetics might be to blame for the development of psoriasis, and having a family history of the condition could increase your risk of developing it. But genetics and a family history alone are not enough to lead to its development. 

Psoriasis occurs due to genetics and environmental factors that trigger the immune system to attack healthy tissue. Such triggers include stress, skin injuries, infections, and medications. 

There is a misconception that psoriasis is contagious, which isn't true. Psoriasis is an autoimmune disease, which means you cannot acquire it by touching affected skin or being near someone with the condition.