Spondyloarthritis — also called spondylitis — refers to a group of inflammatory conditions that primarily affect the spine and nearby joints. These conditions cause inflammation (swelling and irritation) where tendons and ligaments attach to bones, often leading to pain and stiffness in the back and hips.

Health experts don’t know exactly what causes spondyloarthritis, but research suggests that a mix of genetic, immune system, and environmental factors play a role. In some people, spondylitis occurs alongside other related conditions, such as psoriatic arthritis or inflammatory bowel disease. In others, it develops on its own. The cause may vary depending on the type of spondyloarthritis you have.

In this article, you’ll learn about the main causes and risk factors linked to spondylitis and when to talk with a healthcare provider about possible symptoms.

What Are the Main Causes and Risk Factors of Spondylitis?

Some people are more likely to get spondylitis than others. Having certain genes or environmental risk factors can increase your chances. The different types of spondylitis share many risk factors, but they may vary slightly with each type. Here are four factors that may increase the risk of developing spondylitis.

1. Age and Sex

The symptoms of spondylitis usually begin in early adulthood. It’s often diagnosed before the age of 45. The most common form of spondylitis is radiographic axial spondyloarthritis (r-axSpA) — also known as ankylosing spondylitis (AS). The condition causes inflammation mainly in the spine and the sacroiliac joints, which connect the spine to the pelvis.

About 80 percent of people who have ankylosing spondylitis develop symptoms before their 30th birthday. Most people start noticing symptoms during their 20s or 30s.

According to the Arthritis Foundation, past research suggested that men were three times more likely to develop ankylosing spondylitis than women. However, it’s now known that women with spondylitis are more often underdiagnosed or misdiagnosed. Current evidence suggests that axial spondyloarthritis affects people of all sexes at similar rates.

2. Autoimmune Conditions

Spondylitis is an autoimmune disease, meaning the immune system becomes overactive and mistakenly attacks the body’s own healthy tissues. In spondylitis, this reaction targets the joints between the bones of the spine (the vertebrae) and nearby connective tissues. The result is inflammation that can cause pain, stiffness, and long-term joint damage if not treated.

Having one autoimmune condition increases the chance of developing another. People who already have autoimmune diseases — or who have a family history of them — may have a higher risk of developing spondylitis.

Certain forms of spondylitis are linked to other autoimmune conditions. For example, psoriasis is an autoimmune skin disease that can also affect the joints, leading to psoriatic arthritis (PsA). In some people, spinal inflammation (spondylitis) develops as part of PsA.

There’s also a strong connection between inflammatory bowel diseases (IBDs) — such as Crohn’s disease and ulcerative colitis — and ankylosing spondylitis. Studies show that 3 percent to 4 percent of people newly diagnosed with AS also have IBD, and around 10 percent develop IBD within 20 years of their AS diagnosis.

Health experts believe inflammation in the digestive tract may influence inflammation in the spine, but the exact cause of this overlap isn’t yet fully understood. This connection is sometimes called the “gut-joint axis.”

3. Genetics

Like many health conditions, spondylitis seems to run in families. The genetic connection seems to be especially apparent in people with ankylosing spondylitis. Having a parent or a sibling with AS may increase your chances by 10 to 20 times. That may sound like a lot, but it’s far from a guarantee that you’ll develop AS.

For identical twins, if one has AS, the other has about a 50 percent chance of developing it. These patterns show that both genetic and environmental factors contribute to spondylitis — genes may increase your risk, but something else, such as an immune trigger or infection, is often needed to start the disease process.

One gene in particular, called HLA-B27, plays a major role. This gene helps the immune system tell the difference between the body’s own proteins and harmful invaders. Many people with spondyloarthritis test positive for HLA-B27, but not everyone.

The HLA-B27 gene is more common in some populations than others. Among people of northern European descent with AS, as many as 90 percent have the gene. The connection is weaker in Black Americans, Hispanics, and Chinese Americans, according to the Arthritis Foundation. In Japan, HLA-B27 is uncommon in the general population.

Testing positive for HLA-B27 doesn’t mean you’ll develop AS. Only about 5 percent to 10 percent of people with the HLA-B27 gene ever develop the disease. Doctors usually don’t test for HLA-B27 unless you have symptoms — such as persistent back pain and stiffness — that suggest spondyloarthritis. Diagnosing spondylitis requires more than a genetic test; it also involves blood work, imaging, and a physical exam.

4. Environmental Triggers

Genes alone don’t cause spondylitis. Most health experts believe that environmental and lifestyle factors can help trigger the disease in people who are already genetically predisposed.

For instance, bacterial infections — particularly in the gastrointestinal (GI) tract — may activate the immune system in ways that lead to inflammation in the spine. Researchers think that inflammation in the GI tract may influence inflammation in other parts of the body, such as the joints and spine.

There’s also growing research into the gut microbiome, which are the trillions of bacteria that live in the intestines and play an important role in immune function. An imbalance in these bacteria (called dysbiosis) may contribute to autoimmune diseases such as spondyloarthritis, though scientists are still working to understand exactly how.

Other factors, like smoking, stress, and higher body weight, have also been linked to more inflammation in spondylitis. These factors may contribute to increased disease activity by raising the body’s overall inflammation levels. Taking steps to support your physical and emotional health — such as staying active, managing stress, avoiding tobacco, and maintaining a balanced diet — can help reduce inflammation and support your immune system.

Talk to Your Healthcare Provider

Spondylitis can affect people of any age or sex, so it’s important to pay attention to possible symptoms and talk with your healthcare provider early. If you have ongoing back pain or stiffness — especially if it’s worse in the morning or improves with movement — or if you notice related symptoms such as uveitis (eye pain or redness) or digestive problems, it’s a good idea to get checked. Other signs can include neck pain, fatigue, or a feeling of tightness or restricted movement in the chest or ribcage.

On average, it takes about six to seven years for people with axial spondyloarthritis to receive a diagnosis. This delay often happens because chronic back pain is commonly attributed to mechanical causes — like muscle strain or posture — rather than inflammation. Raising awareness among healthcare professionals and the general population can help shorten this gap, leading to earlier treatment and a better quality of life.

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