Lupus isn’t caused by a single thing. It develops when a combination of genetic susceptibility, hormonal factors, and environmental triggers pushes the immune system into attacking the body’s own tissues. No one “catches” lupus the way you catch a cold, and there’s rarely one clear moment that causes it. Instead, multiple factors layer on top of each other until the immune system tips out of balance.
Genetics Set the Stage
Lupus runs in families, but it’s not as simple as inheriting a single gene. Dozens of genes contribute to lupus risk, each one nudging the immune system toward overreactivity. One of the most important is a gene called HLA-DRB1, which helps immune cells distinguish the body’s own proteins from foreign invaders. Certain variants of this gene are strongly linked to lupus, though the specific variants differ by ethnic background. In white populations, one variant (HLA-DR3) carries the most risk, while in East Asian populations, a different variant (HLA-DR15) is more strongly associated.
Other genes involved in lupus affect how immune signals are transmitted and how the body responds to viruses. But having these gene variants doesn’t guarantee you’ll develop lupus. Most people with a genetic predisposition never do. What genetics create is a lower threshold, meaning it takes less of an environmental push to trigger the disease.
Hormones Explain the Gender Gap
Nine out of every ten people with lupus are women, and estrogen is a major reason why. Estrogen doesn’t cause lupus on its own, but it amplifies the immune responses that drive the disease. In people who already have lupus-related antibodies circulating in their blood, estrogen activates immune cells called monocytes through a receptor on their surface. This ramps up the production of inflammatory molecules that contribute to tissue damage, particularly in the skin.
This hormonal influence explains why lupus most commonly appears during the reproductive years, roughly between ages 15 and 44, when estrogen levels are highest. Flares can also worsen during pregnancy or with estrogen-containing medications.
Environmental Triggers That Push the Immune System Over
For someone with the right genetic and hormonal backdrop, certain environmental exposures can be the final push that sets lupus in motion or triggers a flare.
Ultraviolet Light
Sunlight is one of the best-documented triggers. When UV-B rays hit the skin, they cause skin cells to die in a specific way that exposes proteins normally hidden inside the cell. In someone predisposed to lupus, the immune system recognizes these exposed proteins as threats and produces antibodies against them. Those antibodies then attack healthy skin cells displaying the same proteins, creating a cycle of inflammation and tissue damage. This is why sun exposure can trigger both skin rashes and broader disease flares.
Infections
The Epstein-Barr virus (the virus that causes mono) has long been linked to lupus. The theory is that the virus’s proteins resemble the body’s own proteins closely enough to confuse the immune system, a process called molecular mimicry. Research from the CDC suggests that repeated or reactivated Epstein-Barr infections, not just the initial exposure, are associated with lupus development. Nearly all lupus patients show evidence of past Epstein-Barr infection, at higher rates than the general population.
Chemical Exposures and Smoking
Occupational exposure to crystalline silica, a fine dust generated by farming, mining, and construction work, significantly increases lupus risk. People with medium-level silica exposure had roughly double the risk of developing lupus, while those with high exposure had more than four times the risk. Smoking alone wasn’t strongly linked to lupus in one large CDC-funded study, but the combination of smoking and silica exposure was particularly dangerous, raising the risk more than sixfold.
Epigenetic Changes in Immune Cells
One of the more revealing findings in lupus research involves epigenetics, changes in how genes are read without altering the DNA itself. In lupus patients, immune cells show widespread reductions in a chemical tag called DNA methylation, which normally keeps certain genes switched off. When methylation drops, genes involved in the interferon response (a key inflammation pathway) become overactive. This makes the immune system hypersensitive to signals that trigger inflammation.
This pattern appears in T-cells, B-cells, and monocytes from lupus patients, and it shows up even in immature immune cells, suggesting the change is established early in immune cell development. Notably, certain medications that reduce DNA methylation can actually induce lupus-like symptoms in mice, which connects directly to the phenomenon of drug-induced lupus.
Medications That Can Trigger Lupus
Some people develop a lupus-like condition as a side effect of medication. Drug-induced lupus is distinct from the spontaneous form: it typically resolves after the medication is stopped. The most common culprits are hydralazine (a blood pressure drug), procainamide (a heart rhythm medication), isoniazid (a tuberculosis treatment), and TNF-alpha inhibitors used for autoimmune conditions like rheumatoid arthritis. The antibiotic minocycline and certain anti-seizure medications can also cause it. More recently, cancer immunotherapy drugs have been added to the list.
Drug-induced lupus tends to cause joint pain and general inflammation but rarely involves the kidneys or brain, which separates it from the more severe forms of systemic lupus.
Who Is Most at Risk
Lupus affects people across all demographics, but certain groups face substantially higher risk. Black and American Indian/Alaska Native women are two to three times more likely than white women to develop lupus. Hispanic and Asian populations are also affected at higher rates than white populations. These differences reflect both genetic factors (different HLA variants are more common in different ethnic groups) and likely socioeconomic and environmental exposures that vary across communities.
Family history matters too. If you have a first-degree relative with lupus, your own risk is meaningfully elevated, though still far from certain. Identical twins share lupus only about 25 to 50 percent of the time, reinforcing that genes alone aren’t enough.
The Gut Microbiome Connection
Lupus patients consistently show an altered balance of gut bacteria compared to healthy individuals. They tend to have lower levels of Firmicutes bacteria and a higher proportion of Bacteroidetes, along with increases in certain Streptococcus species normally found in the mouth. This imbalance, known as dysbiosis, may contribute to immune dysfunction by promoting inflammatory immune cell types and weakening the intestinal barrier.
Animal studies have shown that specific probiotic strains, particularly certain lactobacilli, can repair intestinal permeability and shift the immune environment toward less inflammation. Whether correcting gut dysbiosis could prevent or manage lupus in humans is still being worked out, but the connection between gut health and immune regulation is increasingly clear.