Psoriatic arthritis (PsA) is a type of inflammatory arthritis. It affects about one-third of people with psoriasis. PsA is different from rheumatoid arthritis, but like that condition, PsA also causes joint pain and inflammation throughout the body. While researchers don’t fully understand what causes PsA, they have found both genetic and environmental risk factors.

What Causes Psoriatic Arthritis?

PsA is an autoimmune disease. This means the body’s immune system mistakenly attacks healthy cells and tissues, as if they were harmful viruses or bacteria. In PsA, the immune system targets the ligaments and joints, causing inflammation and damage.

The exact cause of psoriatic arthritis is not understood. However, rheumatologists (doctors who specialize in bones, muscles, internal organs, and joints) and researchers believe that PsA is triggered by a combination of biological and environmental factors.

Genetic Causes

Certain genetic factors have been linked with the development of psoriatic arthritis. Some people are born with certain mutations (changes) in their immune system genes — including HLA-B27, HLA-B8, or HLA-B38 — that make them more likely to develop PsA. These gene types are more common in people with PsA than in people with only psoriasis.

Another gene, HLA-C06, is more closely linked to psoriasis. People with this gene who go on to develop PsA often get it later in life.

Immune System Involvement

An abnormal immune response plays a key role in all types of inflammatory arthritis. This can happen when the body makes too many inflammatory mediators — substances that promote inflammation.

T cells, a type of immune cell, play a major role in PsA. These cells release proteins called cytokines, which act like messengers in the body. Some cytokines cause inflammation, while others help control it.

In people who are genetically prone to PsA, T cells release more cytokines that trigger inflammation. This inflammation leads to joint pain, swelling, and damage. Studies show that higher levels or more active T cells and cytokines often have more severe PsA symptoms.

Environmental Causes

Research shows that certain environmental factors may help trigger psoriatic arthritis. Below are some key factors that may contribute to PsA.

Infections

Studies have found that certain infections may contribute to PsA. For example, infection with the bacteria Streptococcus pyogenes, which causes strep throat, has been connected to a higher PsA risk. Other infections believed to trigger PsA include:

• Chlamydia, a sexually transmitted infection
• Bacteria that cause infectious diarrhea, including species of Campylobacter and Yersinia

Some viruses may also be linked to PsA, including HIV and hepatitis C. Other viruses believed to cause rheumatoid arthritis may also cause PsA, including:

• Parvovirus B19
• Cytomegalovirus
• Epstein-Barr virus

Changes in the gut and skin microbiomes — the natural bacteria and other tiny organisms that live on the skin and help keep it healthy — may also be important. People with PsA often have fewer helpful gut bacteria, which may increase inflammation in the joints. It’s still unclear if these changes cause PsA or are a result of it.

Physical Trauma, Injuries, and Work-Related Activities

Physical trauma, or injuries, to the skin or joints, can sometimes trigger PsA. This is called the Koebner phenomenon (also called Koebnerization). In people with psoriasis, this phenomenon causes new skin lesions to appear at the site of skin injuries like scratches, cuts, or burns. In people with PsA, even minor injuries can trigger a mild immune response, which could cause new lesions to appear.

The Koebner phenomenon may also affect tendons and other tissues, not just the skin. This might explain why people in certain jobs that involve repetitive movements or physical stress are more likely to develop PsA.

What Are the Risk Factors for Psoriatic Arthritis?

There are many risk factors associated with PsA. Although more research is needed to fully understand these risk factors, the following have been known to play a role in developing PsA.

Psoriasis

Psoriasis is a skin condition that causes scaly, discolored patches called plaques. Having psoriasis is the most significant risk factor for PsA. However, people without skin psoriasis can also develop PsA.

According to the National Psoriasis Foundation, PsA develops in about 30 percent of people with psoriasis, often around 10 years after skin symptoms first appear. In 15 percent to 20 percent of cases, PsA symptoms begin before the skin condition develops.

Having psoriasis is the most significant risk factor for PsA. However, people without skin psoriasis can also develop PsA.

People with more severe psoriasis are more likely to get PsA. Certain patterns of psoriasis — such as lesions on the scalp, genitals, or nails — are also associated with a higher risk. Nail changes, including pitting (small dents in the nail surface), may be especially linked to the development of PsA.

Family History

PsA runs in families. About 40 percent of people with PsA have a family member with psoriatic arthritis. This, along with the known links between PsA and certain inherited genes, shows that genetics plays a strong role in who develops PsA. PsA can affect anyone, regardless of sex.

About 40 percent of people with PsA have a family member with psoriatic arthritis.

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Race and Ethnicity

PsA is significantly more common in white people, according to the Arthritis Foundation. However, studies have shown that Asian and Hispanic people tend to have more extensive and severe PsA.

Age

PsA can begin at any age, but it most often develops between ages 30 and 50. Children with psoriasis are also at risk of developing PsA. Most people who are diagnosed with skin psoriasis develop PsA within 10 to 20 years.

Other Environmental Factors

Certain environmental risk factors among people with psoriasis include infections that require antibiotics and jobs or activities that involve performing repetitive movements or lifting heavy loads.

What Triggers Psoriatic Arthritis Flares?

A flare, or flare-up, is when PsA symptoms suddenly get worse. Common triggers for PsA flares include:

• Getting an infection
• Experiencing a physical injury (including sunburn)
• Skipping or stopping PsA medications
• Feeling high levels of stress
• Eating foods that may trigger inflammation, such as those high in sugar, saturated fat, or processed ingredients — or for some people, nightshades, dairy, or gluten

Identifying what triggers your PsA flares — along with consulting a rheumatology provider for treatment — can help you manage your condition better and reduce flare-ups.

Talk With Others Who Understand

MyPsoriasisTeam is the social network for people with psoriasis and psoriatic arthritis and their loved ones. Members come together to ask questions, give advice, and share their stories with others who understand life with psoriasis and psoriatic arthritis.

Do you have psoriatic arthritis? What factors have contributed to your symptoms? Share your experience in the comments below, or start a conversation by posting on MyPsoriasisTeam.