Vasculitis happens when the immune system mistakenly attacks blood vessel walls, causing inflammation that can narrow, weaken, or scar them. The triggers behind this immune malfunction vary widely, from infections and medications to autoimmune diseases, genetic predisposition, and environmental exposures. In many cases, the exact cause is never identified, but understanding the known triggers helps explain why the condition develops and who faces the greatest risk.
How the Immune System Damages Blood Vessels
Regardless of the specific trigger, vasculitis follows a common pattern: the immune system treats blood vessel walls as a threat and launches an inflammatory attack against them. The details of that attack differ depending on which size of vessel is involved.
In large vessels like the aorta and its major branches, immune cells called dendritic cells appear to recognize an unknown substance in the vessel wall and activate a chain of inflammation that spreads from the outer layer of the vessel inward. This is what happens in giant cell arteritis and Takayasu arteritis. In medium-sized vessels, the damage often stems from immune complexes, clumps of antibodies bound to foreign particles (like pieces of the hepatitis B virus) that get stuck in vessel walls and trigger an inflammatory response. Inflammatory signaling molecules then drive further injury to the vessel lining.
Small vessel vasculitis works differently. In ANCA-associated vasculitis, the most common form affecting small vessels, the body produces antibodies that target proteins on the surface of neutrophils, a type of white blood cell. These antibodies “prime” neutrophils, essentially switching them on at the wrong time and place. The activated neutrophils latch onto blood vessel walls and release destructive enzymes and reactive oxygen species that eat into the vessel lining. The process is self-reinforcing: as neutrophils die, they release web-like structures that expose more of the proteins the antibodies target, producing even more of those harmful antibodies.
Infections That Trigger Vasculitis
Certain infections are well-established vasculitis triggers. Hepatitis B is perhaps the best known. The virus sheds particles into the bloodstream that combine with the body’s antibodies to form immune complexes. These complexes lodge in medium-sized blood vessel walls and provoke inflammation, leading to a condition called polyarteritis nodosa. Hepatitis B can also trigger cryoglobulinemic vasculitis, where abnormal antibodies clump together in cold temperatures and damage small vessels.
Hepatitis C is strongly linked to cryoglobulinemic vasculitis through a similar immune complex mechanism. Other infections, both bacterial and viral, can produce a form of small vessel inflammation called leukocytoclastic vasculitis, where the skin develops purplish spots from damaged capillaries. The infection doesn’t need to be in the blood vessels themselves. The immune response it provokes elsewhere in the body can spill over into vascular tissue.
Medications as a Cause
Drug-induced vasculitis is uncommon but well documented. The medications with the strongest evidence include hydralazine (a blood pressure drug), certain antibiotics like minocycline and nitrofurantoin, sulfasalazine (used for inflammatory bowel disease and rheumatoid arthritis), and d-penicillamine. Propylthiouracil, used to treat overactive thyroid, is another established culprit. These drugs can stimulate the body to produce ANCA, the same neutrophil-targeting antibodies found in primary vasculitis, essentially mimicking an autoimmune disease.
Biologic medications designed to suppress inflammation, particularly TNF-alpha inhibitors like adalimumab, infliximab, and etanercept, have also been linked to vasculitis in rare cases. This is paradoxical since these drugs treat inflammatory conditions, yet they can occasionally shift immune activity in a way that provokes vessel inflammation. Other less common triggers include the seizure medication phenytoin, the gout drug allopurinol, and certain antibiotics including vancomycin and ciprofloxacin. Drug-induced vasculitis typically improves after the medication is stopped, though some cases require additional treatment.
Autoimmune Diseases and Vasculitis
Vasculitis frequently develops as a complication of existing autoimmune conditions. Lupus is the most prominent example. Roughly 50% of people with systemic lupus erythematosus develop some form of vasculitis during their disease course, most commonly affecting small vessels. In lupus, the body produces antibodies against its own DNA and cell components. These antibodies combine with their targets to form immune complexes that deposit in vessel walls. The complement system, a set of proteins that amplifies immune responses, then activates and attracts white blood cells that infiltrate and destroy the vessel tissue with collagenase and elastase enzymes.
Anti-endothelial cell antibodies are found in more than 80% of lupus patients and directly damage the cells lining blood vessels. Antiphospholipid antibodies, present in many lupus patients, compound this damage by binding to already-injured vessel surfaces and worsening endothelial destruction. Rheumatoid arthritis, Sjögren syndrome, and inflammatory bowel disease can also produce secondary vasculitis through related immune complex mechanisms, though less frequently than lupus.
Genetic Predisposition
Vasculitis is not inherited in a simple pattern, but specific genetic variants significantly raise the risk. The strongest associations involve HLA genes, which help the immune system distinguish the body’s own cells from foreign invaders. A variant in the HLA-DPB1 gene increases the risk of ANCA-associated vasculitis nearly fourfold. Another variant, HLA-DRB1*09:01, raises the risk by about 70% for certain subtypes of small vessel vasculitis.
These genetic links help explain why some forms of vasculitis cluster in particular populations. Giant cell arteritis is most common in people of Northern European descent. Kawasaki disease is far more prevalent in East Asian populations, particularly Japan, where roughly 1 in 64 boys and 1 in 80 girls develop it before age 10. Behçet syndrome concentrates along the ancient Silk Road regions of the Middle East and East Asia. Genetics don’t cause vasculitis on their own, but they create a landscape of susceptibility that other triggers exploit.
Environmental and Occupational Exposures
Silica dust is the best-studied environmental trigger. People with sustained occupational exposure to silica, common in mining, drilling, textile manufacturing, and painting, face a 3.4 to 7-fold increased risk of developing the ANCA antibodies that drive small vessel vasculitis. A meta-analysis of six case-control studies confirmed silica exposure is positively associated with ANCA-associated vasculitis incidence. Farming also raises risk, with regular exposure to livestock and agricultural environments linked to higher rates of several vasculitis subtypes.
Heavy metals including cadmium, lead, and mercury have been associated with increased risk of granulomatosis with polyangiitis, one of the ANCA-associated types. Industrial solvents like trichloroethylene and vinyl chloride show similar associations. Carbon monoxide exposure, as an air pollutant, has also been positively correlated with vasculitis incidence in population-level data, though other common air pollutants like particulate matter and nitrogen dioxide have not shown the same link. The relationship between smoking and vasculitis remains unclear, with studies producing conflicting results. Some suggest smoking raises risk, particularly for certain antibody subtypes, while others suggest a possible protective effect.
Cancer as an Underlying Cause
Vasculitis occasionally develops as a paraneoplastic syndrome, meaning the cancer itself provokes the immune response that damages blood vessels. About 77% of cancer-associated vasculitis cases involve blood cancers like lymphoma and leukemia. Among solid tumors, lung cancer and colon cancer are the most frequently linked, followed by kidney, bladder, prostate, and breast cancers. Paraneoplastic vasculitis is rare, but it makes identifying the underlying cause important, especially when vasculitis appears in someone without other obvious risk factors.
Who Is Most at Risk
Different types of vasculitis strike different demographic groups, which offers clues about their causes. Giant cell arteritis occurs exclusively in people over 50 and is two to three times more common in women. Takayasu arteritis, which affects the same large vessels, skews the opposite direction, mainly appearing in women under 40. Polyarteritis nodosa peaks between ages 40 and 60 and favors men at a ratio of about 1.5 to 1.
ANCA-associated vasculitis, the most common primary form in adults, peaks in people aged 65 to 74 and is slightly more common in men. Kawasaki disease is almost entirely a childhood condition, affecting children under 5. Behçet syndrome typically appears in the 20s and 30s and affects men and women at similar rates, though men tend to experience more severe disease. These demographic patterns reflect the interplay of genetics, hormonal influences, accumulated environmental exposures, and age-related changes in immune function that together shape who develops vasculitis and when.