Introduction
Relapsing polychondritis is caused by an abnormal immune response that directs inflammation against the body’s own cartilage and certain other connective tissues. In practical terms, the condition develops when the immune system loses tolerance to structural proteins in cartilage, especially in the ears, nose, airways, and joints, and begins to damage them repeatedly over time. The exact trigger is often not identifiable, but the disease appears to arise from a combination of autoimmune mechanisms, genetic susceptibility, and environmental or infectious factors that disturb immune regulation.
The causes are best understood in categories: the core biological mechanism is autoimmune cartilage injury, while the factors that shape that process include inherited risk, immune system activation by external exposures, overlap with other autoimmune disorders, and in some cases a preceding infection or inflammatory event. No single cause explains every case, which is why relapsing polychondritis is considered a multifactorial immune-mediated disease.
Biological Mechanisms Behind the Condition
The central biological problem in relapsing polychondritis is immune-mediated inflammation directed at cartilage. Cartilage is a specialized connective tissue that normally has very few cells and little blood supply. Because it is relatively isolated from the immune system, it is usually protected from immune attack. In relapsing polychondritis, that protection appears to fail. Immune cells recognize components of cartilage as if they were foreign, leading to repeated cycles of inflammation and tissue injury.
One of the most important suspected targets is type II collagen, a major structural protein in cartilage. Other cartilage-related proteins, including matrilin-1 and cartilage oligomeric matrix protein, may also become immune targets. When immune tolerance to these proteins breaks down, T lymphocytes and antibodies can contribute to inflammation. Cytokines such as tumor necrosis factor alpha, interleukin-1, and interleukin-6 help amplify the inflammatory response, recruiting more immune cells into the tissue and increasing destruction of the cartilage matrix.
This process explains the relapsing pattern. Inflammation does not remain continuously constant; instead, it flares when immune activity intensifies and partially quiets when the inflammatory response subsides. However, each flare may leave behind structural damage. Over time, repeated injury can weaken cartilage, alter tissue shape, and impair the function of structures that depend on it, such as the ear, nose, and trachea. The same immune activity may also affect proteoglycan-rich tissues outside cartilage, which helps explain why the disease can involve the eyes, heart valves, blood vessels, and inner ear in some people.
A key feature of the disease is that cartilage damage is not purely mechanical or degenerative. It is driven by immunologic inflammation. Chondrocytes, the cells that maintain cartilage, are injured both directly by immune attack and indirectly by the inflammatory environment. As cartilage matrix breaks down, new fragments may be exposed to the immune system, which can further intensify the response and perpetuate the cycle.
Primary Causes of Relapsing polychondritis
The most important cause is autoimmunity. In autoimmune disease, the immune system mistakes normal self-tissues for threats. In relapsing polychondritis, the primary autoimmune target appears to be cartilage. This loss of immune tolerance may occur because immune regulatory pathways fail to suppress autoreactive T cells and B cells. Once that tolerance breaks, inflammatory mediators damage cartilage and surrounding tissues. Autoimmunity is the main mechanism because it explains both the tissue specificity and the recurrent nature of the disease.
A second major cause is immune dysregulation, which refers to broader abnormalities in how the immune system is controlled. Some people may not have a single clear autoimmune trigger, but they may have an immune system that responds excessively to normal tissue antigens or resolves inflammation poorly. Abnormal antigen presentation, altered T-cell regulation, and heightened cytokine signaling can all contribute to persistent inflammation. In this setting, cartilage becomes a vulnerable target because it contains proteins that can provoke immune recognition once tolerance is lost.
A third important factor is cross-reactive immune activation after infection or tissue injury. In some cases, the immune system may respond to a microbial protein that resembles a cartilage protein, a phenomenon known as molecular mimicry. If immune cells are activated against that microbial target, they may also react with cartilage components. Tissue injury may also expose hidden cartilage antigens that are normally inaccessible, giving the immune system an opportunity to become sensitized. These mechanisms do not cause every case, but they are biologically plausible pathways by which relapsing polychondritis can begin.
A fourth cause is association with other autoimmune disease. Relapsing polychondritis often appears in the context of broader autoimmune reactivity rather than as a completely isolated phenomenon. When a person already has immune-mediated disease, their immune system may be more prone to losing self-tolerance in additional tissues. This does not mean one disease directly transforms into another, but it suggests that the same biological tendency toward autoimmunity can manifest in multiple organ systems, including cartilage.
Contributing Risk Factors
Genetic influences can increase susceptibility, although no single gene is known to cause relapsing polychondritis on its own. Certain immune-related genetic backgrounds, including variations in human leukocyte antigen, or HLA, genes, may shape how antigens are presented to T cells. If cartilage-derived peptides are presented in a way that promotes autoimmunity, the risk of disease may rise. Genetic factors are therefore best understood as a predisposition to abnormal immune recognition rather than a direct cause.
Environmental exposures may contribute by provoking immune activation in a person who is already susceptible. Respiratory infections, repeated inflammation of mucosal surfaces, pollutants, or other immune-stimulating exposures may all provide the inflammatory context in which self-tolerance is disrupted. Environmental triggers are not proven to cause the disease in a universal way, but they may help initiate or intensify immune responses that target cartilage.
Infections are among the most discussed potential contributors. Bacterial or viral infections can activate immune cells, increase cytokine production, and expose the body to antigens that resemble self-proteins. After an infection, the immune system may remain in an activated state long enough to misdirect its response toward cartilage. Infection may also damage tissue and reveal antigens that were previously hidden from immune surveillance. This makes infection a plausible trigger rather than a sole explanation.
Hormonal influences may also play a role, particularly because many autoimmune diseases vary in frequency according to sex and immune status. Sex hormones can alter immune responsiveness by affecting T-cell activity, antibody production, and cytokine patterns. While the exact relationship in relapsing polychondritis is not fully defined, hormonal differences may influence who develops the disease and how aggressively the immune system behaves once it is activated.
Lifestyle factors are less clearly established as direct causes, but they can influence immune function. Chronic stress, sleep disruption, smoking, and poor overall health can alter inflammatory signaling and immune regulation. Smoking, for example, can affect airway tissues and promote chronic inflammation, which may be relevant in a disease that often involves the respiratory tract. These factors are best viewed as modifiers of immune balance rather than primary causes.
How Multiple Factors May Interact
Relapsing polychondritis is rarely the result of one isolated event. More often, it appears when several biological conditions align. A person may inherit a tendency toward immune dysregulation, then encounter an infection or environmental exposure that activates the immune system. If the activation is strong enough, cartilage antigens may be presented to immune cells in a way that promotes loss of tolerance. Once autoreactive cells are established, ongoing cytokine signaling and local tissue injury can maintain the inflammatory cycle.
This interaction is important because the immune system does not operate in separate compartments. Innate immune activation can influence adaptive immunity, adaptive immune responses can reinforce tissue inflammation, and damaged cartilage can itself become a source of further antigen exposure. In other words, initial triggers may fade, but the disease can continue because the immune response has become self-sustaining. That is one reason the condition may remain chronic and relapsing even when the original trigger is no longer evident.
Variations in Causes Between Individuals
The causes of relapsing polychondritis differ from one person to another because the immune system is shaped by many personal factors. Genetics determine part of the baseline susceptibility, especially in how antigens are presented and how immune tolerance is regulated. Some individuals may have a stronger autoimmune predisposition, while others may need a larger external trigger before disease appears.
Age can also influence cause and expression. Although the disease can develop at almost any age, immune regulation changes over the life course. Younger immune systems may respond differently to infections or environmental stimuli than older ones, and age-related changes in immune balance may alter disease risk or severity.
Health status matters because chronic inflammatory conditions, other autoimmune diseases, and immune-modifying medications can all affect immune behavior. A person with existing immune activation may be more vulnerable to developing cartilage-directed autoimmunity. By contrast, someone with fewer immune stressors may require a different trigger or may never develop the disease even if they carry some genetic risk.
Environmental exposure patterns also differ widely. Some people encounter recurrent respiratory infections, occupational irritants, or smoking exposure, while others do not. These differences may help explain why relapsing polychondritis appears in some people and not others, even when the underlying autoimmune mechanism is similar.
Conditions or Disorders That Can Lead to Relapsing polychondritis
Relapsing polychondritis can occur alongside or after other immune-mediated disorders, and these conditions may help create the immunologic setting in which cartilage inflammation develops. Autoimmune diseases such as rheumatoid arthritis, systemic lupus erythematosus, vasculitis, and Sjogren syndrome are among the conditions most often reported in association with relapsing polychondritis. These disorders share a common theme of dysregulated immune tolerance, so their presence suggests a broader autoimmune tendency rather than a separate unrelated process.
Some hematologic disorders, including myelodysplastic syndromes and other bone marrow abnormalities, have also been linked to relapsing polychondritis. In these settings, abnormal immune signaling or altered blood cell development may contribute to inappropriate immune activation. The exact direction of causality is not always clear. In some patients, the marrow disorder may help trigger immune dysfunction; in others, both conditions may arise from a shared underlying immune abnormality.
Infections can also precede the condition or act as triggers in susceptible individuals. The relationship is usually indirect: infection activates the immune system, raises inflammatory signals, and may create cross-reactive antibodies or T cells. Once the immune response is established, it may continue to attack cartilage even after the infection resolves. This means that an infection may be the event that reveals the disease rather than the sole cause of it.
Conclusion
Relapsing polychondritis develops because the immune system targets cartilage and related connective tissues, most likely through autoimmune mechanisms that break normal tolerance to cartilage proteins. The most important biological cause is immune-mediated inflammation, supported by cytokine-driven tissue injury and recurrent immune activation. Genetic predisposition, infections, environmental exposures, and associated autoimmune or hematologic disorders can all contribute by making immune misdirection more likely or by triggering the first inflammatory episode.
The condition does not arise from a single pathway in every patient. Instead, it reflects an interaction between immune susceptibility, external triggers, and tissue-specific vulnerability. Understanding these mechanisms explains why the disease can be unpredictable, why it may recur over time, and why it often appears in the setting of broader immune dysfunction rather than in complete isolation.