What Causes Ankylosing Spondylitis?

Experts are still investigating its origins

Ankylosing spondylitis (AS) is a chronic, debilitating, painful type of inflammatory arthritis that affects the spine. Researchers are still working to understand what causes AS. However, it is thought that a variety of factors increase one’s risk of the disease, including certain genetic and environmental factors. Men and young to middle-aged adults may also be more likely to get the disease.


What Is Ankylosing Spondylitis?

Environmental Causes

Researchers speculate that there may be environmental contributors that increase one’s risk of AS. However, these are currently not well understood. Some of the environmental causes of AS may include:

  • exposure to certain infections
  • exposure to certain toxins
  • mechanical stress/injury to the affected joints
  • changes in the microbiome (the population of bacteria that inhabit your colon)
  • inflammation of the bowel

Genetic Causes

People with variations of certain genes are more likely to get AS. One such gene variant is known as HLA-B27. The HLA gene is used to make an important protein for the immune system. Ninety percent of people diagnosed with AS test positive for the HLA-B27 variant.

It's important to note, however, that not everyone with the HLA-B27 gene variation gets the disease, which means that factors other than genetics must play a role.

Other genes are also thought to play a role in increasing one’s risk of AS, including a gene known as ERAP-1. Other genes involved with the immune system may also play important roles.

Senior man got up from couch felt low back pain
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Physiological Causes

Researchers are still working to untangle the possible physiological contributors to AS. It is thought to at least partly arise from alterations in a person’s immune system. For example, researchers currently believe that an immune signaling molecule known as IL-17 may play an important role in the disease.

Other Risk Factors

For reasons that researchers don’t fully understand, AS is also more likely to occur in certain groups of people than in others. It is important to note that many people who do not have these risk factors get the disease as well.

You may be more likely to get diagnosed with AS if you are a male, Caucasian, and/or between the ages of 17 and 45.

While it used to be thought that AS predominantly affected men, in recent years it has become clearer that this may not be the case. It may be that almost as many women are affected by the condition as men.

Some researchers claim that AS is currently underdiagnosed in women, partly because women often display somewhat different symptoms than men.

It is possible that sex itself plays some sort of causal role in the disease. For example, a study in Arthritis and Rheumatism found some different patterns of immune responses in women with AS compared to men. This may point to some underlying physiological differences in how the disease appears in women.

Lifestyle Risk Factors

It's not known if smoking increases the risk of AS, though there is some evidence to suggest it may. However, it does seem to worsen existing disease symptoms.

Lack of exercise may be a risk for more severe disease. A daily exercise regimen can help keep you limber and strong, and decrease the disease's impact on your life. Strengthening certain muscles will allow you to maintain better posture, which can decrease your chance of the abnormal curving of the spine known as kyphosis.

Your healthcare provider or a physical therapist can suggest an appropriate exercise plan for you.

As you manage your AS, one of the most important things you can do is to seek regular treatment and follow your healthcare provider's advice. This will minimize your chances of getting severe complications from AS.

Ankylosing Spondylitis Healthcare Provider Discussion Guide

Get our printable guide for your next healthcare provider's appointment to help you ask the right questions.

Doctor Discussion Guide Man


AS is a disease of multi-factorial causes which researchers are still trying to fully understand. It’s likely that various environmental and genetic factors come together to trigger the disease in any single person. Unfortunately, at this time, not much is known about how one might decrease one’s risk of getting AS.

Frequently Asked Questions

  • How common is ankylosing spondylitis?

    Worldwide, 0.1% to 1.4% of people are affected by AS. Men tend to be affected more severely and more often—at almost twice the rate—of women, while women frequently take longer to be diagnosed.

  • How many people with ankylosing spondylitis have the HLA-B27 gene?

    Of people who have AS, 90% to 95% have the HLA-B27 gene, which is connected to inflammatory conditions of the joints.

  • Is there a way to prevent ankylosing spondylitis?

    At present, there is no known way to prevent the development of AS. A combination of environmental factors and genetic predisposition may combine to cause this condition. However, eating an anti-inflammatory diet, exercising, and otherwise taking care of your health are always wise. If you do develop AS, being in good physical health can help you better cope with it.

9 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Simone D, Al mossawi MH, Bowness P. Progress in our understanding of the pathogenesis of ankylosing spondylitis. Rheumatology (Oxford). 2018;57(suppl_6):vi4-vi9. doi:10.1093/rheumatology/key001

  2. Akassou A, Bakri Y. Does HLA-B27 Status Influence Ankylosing Spondylitis Phenotype? Clin Med Insights Arthritis Musculoskelet Disord. 2018;11:1179544117751627. doi:10.1177/1179544117751627

  3. Spondylitis. Cleveland Clinic.

  4. Haroon NN, Paterson JM, Li P, Haroon N. Increasing proportion of female patients with ankylosing spondylitis: a population-based study of trends in the incidence and prevalence of AS. BMJ Open. 2014;4(12):e006634. doi:10.1136/bmjopen-2014-006634

  5. Kaut IK, Abourazzak FE, Jamila E, Sènami FA, Diketa D, Taoufik H. Axial Spondyloarthritis and Cigarette Smoking. Open Rheumatol J. 2017;11:53-61. doi:10.2174/1874312901711010053

  6. Ankylosing Spondylitis: An Overview. Hospital for Special Surgery.

  7. Dean LE, Jones GT, MacDonald AG, Downham C, Sturrock RD, Macfarlane GJ. Global prevalence of ankylosing spondylitis. Rheumatology (Oxford). 2014 Apr;53(4):650-7. doi:10.1093/rheumatology/ket387

  8. Rusman T, van Vollenhoven RF, van der Horst-Bruinsma IE. Gender differences in axial spondyloarthritis: Women are not so lucky. Curr Rheumatol Rep. 2018;20(6):35. doi:10.1007/s11926-018-0744-2

  9. Andersson G, McNeill T. Lumbar Spine Syndromes, Evaluation and Treatment. New York: Springer Verlag Wien; 1989:180-181.

Additional Reading
  • Gracey E, Yao Y, Green B, et al. Sexual dimorphism in the Th17 signature of ankylosing spondylitis. Arthritis Rheumatol. 2016;68(3):679-89. DOI: 10.1002/art.39464

  • Haroon NN, Paterson JM, Li P, et al. Increasing proportion of female patients with ankylosing spondylitis: a population-based study of trends in the incidence and prevalence of AS. BMJ Open. 2014;4(12):e006634. DOI: 10.1136/bmjopen-2014-006634

  • Kaut IK, Abourazzak FE, Jamila E, et al. Axial spondyloarthritis and cigarette smoking. Open Rheumatol J. 2017;11:53-61. DOI: 10.2174/1874312901711010053

  • Reveille JD. Epidemiology of spondyloarthritis in North America. Am J Med Sci. 2011;341(4):284-6. DOI: 10.1097/MAJ.0b013e31820f8c99

  • Simone D, Al Mossawi MH, Bowness P. Progress in our understanding of the pathogenesis of ankylosing spondylitis. Rheumatology (Oxford). 2018;57(suppl_6):vi4-vi9. DOI: 10.1093/rheumatology/key001

By Anne Asher, CPT
Anne Asher, ACE-certified personal trainer, health coach, and orthopedic exercise specialist, is a back and neck pain expert.