Lupus is caused by a combination of genetic susceptibility, hormonal factors, and environmental triggers that together push the immune system into attacking the body’s own tissues. No single cause has been identified. Instead, most researchers describe it as a “perfect storm” where someone with the right genetic makeup encounters specific triggers that flip the immune system from protective to destructive.
An estimated 204,000 people in the United States have systemic lupus erythematosus (SLE), the most common form. Nine out of ten are women, and women of childbearing age (15 to 44) carry the highest risk. Black and American Indian/Alaska Native women are two to three times more likely to develop lupus than white women.
How the Immune System Goes Wrong
In a healthy immune system, white blood cells learn to distinguish the body’s own cells from foreign invaders. In lupus, this distinction breaks down at multiple levels. The two main types of immune cells involved, T cells and B cells, both malfunction in specific ways.
T cells in people with lupus are abnormally activated and produce too little of a key signaling molecule called IL-2 that normally helps regulate immune responses. At the same time, they overproduce inflammatory signals that amplify the attack on healthy tissue. A subset of T cells called regulatory T cells, which act as brakes on the immune system, are reduced in number or don’t work properly. Without these brakes, the immune response spirals.
B cells, which produce antibodies, become hyperactive. People with active lupus show increased numbers of self-reactive B cells, meaning cells that have been programmed to attack the body’s own proteins instead of bacteria or viruses. This represents a failure in one of the immune system’s earliest safety checks: the process that normally weeds out self-attacking B cells before they mature. The result is a flood of autoantibodies, proteins that target the body’s own DNA, joints, kidneys, skin, and other organs.
Genetics Set the Stage
Lupus runs in families, though inheriting the relevant genes doesn’t guarantee you’ll develop the disease. The strongest genetic links involve specific variations in a group of immune system genes called HLA (human leukocyte antigen), which help the immune system identify what belongs in the body and what doesn’t.
Two specific HLA variants, known as DR2 and DR3, appear in nearly two-thirds of lupus cases. People who carry both variants together, or two copies of DR3, have the highest risk. These gene variants also influence which types of autoantibodies a person produces, which in turn shapes how the disease behaves. For instance, the DR3 variant is linked to antibodies that target proteins called Ro and La, while DR2 is associated with antibodies against a protein called Sm. People carrying both DR2 and DR3 are especially likely to develop multiple types of autoantibodies.
These genes don’t cause lupus on their own. They create a predisposition, a loaded gun that still requires an environmental or hormonal trigger to fire.
Why Lupus Overwhelmingly Affects Women
The 10-to-1 female-to-male ratio in lupus points directly to estrogen, the primary female sex hormone. Estrogen shapes immune function in several important ways, and in people genetically predisposed to lupus, these effects tip the balance toward autoimmunity.
Estrogen normally helps regulate immune tolerance, the process by which the body learns not to attack itself. It does this partly through a gene called AIRE, which plays a central role in training immune cells to recognize the body’s own tissues as safe. Estrogen suppresses this gene’s activity, potentially weakening the immune system’s ability to distinguish self from non-self.
In healthy women, estrogen also promotes the development of regulatory T cells that keep immune responses in check. But in lupus patients, both female and male, this protective response is blunted. The regulatory T cell population fails to expand properly in response to estrogen, removing a critical safety mechanism. Estrogen also increases levels of a small RNA molecule in T cells that dials down a protein involved in immune regulation, potentially pushing the immune system toward hyperactivity. This helps explain why lupus most commonly appears during the reproductive years, when estrogen levels are highest, and why pregnancy and oral contraceptives can trigger flares.
Environmental Triggers
For someone with genetic susceptibility, specific environmental exposures can set the disease in motion or worsen it.
Ultraviolet Light
Photosensitivity is one of the hallmark features of lupus, and UV exposure is one of the best-documented triggers. When UV light hits skin cells, it causes them to die through a process called apoptosis. In most people, the immune system quietly clears away these dead cells. In lupus, the clearance system is defective. Dead skin cells accumulate and spill their internal contents, including DNA and proteins, into the surrounding tissue. The immune system treats this cellular debris as foreign, producing autoantibodies against it. UV exposure also attracts inflammatory immune cells to the skin, generating chemical signals that recruit even more immune activity, creating a self-reinforcing cycle of inflammation.
UV light, particularly in the UVB range, also causes epigenetic changes. It reduces levels of an enzyme responsible for a chemical tag called DNA methylation, which normally keeps certain genes switched off. When this tagging system fails in T cells, genes that should stay silent become active, and the T cells begin reacting against the body’s own tissues.
Epstein-Barr Virus
Epstein-Barr virus (EBV), the virus that causes mononucleosis, is one of the most studied infectious triggers. The connection works through several pathways. First, a protein on the virus’s surface closely resembles proteins found in human cells. The immune system produces antibodies against the viral protein, and those antibodies then cross-react with the body’s own tissues, a process called molecular mimicry.
Second, people with lupus appear to have a harder time keeping EBV in check. Normally, after initial infection, the virus goes dormant and the immune system keeps it suppressed. In lupus patients, the virus reactivates more frequently because their EBV-specific T cells don’t function properly. This leads to a higher viral load and more infected cells. As the immune system repeatedly tries to destroy these infected cells, it releases both viral and cellular debris, generating a constant supply of material that triggers autoantibody production.
Epigenetic Changes
Epigenetics refers to changes in how genes are read and expressed without altering the DNA sequence itself. Think of it as the difference between having a book and having certain pages bookmarked or highlighted. The words don’t change, but which ones get read does.
In lupus, CD4+ T cells show widespread loss of DNA methylation, the chemical tags that normally keep certain genes silenced. When these tags are stripped away, genes that promote immune activation and antibody production get switched on inappropriately. One well-studied example involves a gene that produces a surface protein called LFA-1. When the chemical tags keeping this gene quiet are removed, LFA-1 is overproduced on T cells, which in turn stimulates B cells to churn out antibodies. A similar process affects a gene encoding a protein called CD70, which directly drives B cells to overproduce the antibody IgG.
Small RNA molecules called microRNAs also play a role. Two specific microRNAs found at elevated levels in lupus T cells directly block the enzyme responsible for maintaining DNA methylation, creating a feedback loop that perpetuates the loss of gene silencing across the genome. Changes in how DNA is packaged around proteins called histones compound the problem. Lupus patients show reduced chemical modifications on histones in their T cells, altering which stretches of DNA are accessible and active.
What makes epigenetics particularly relevant is that these changes can be triggered by the same environmental factors already linked to lupus: UV light, infections, and certain medications.
Drug-Induced Lupus
Certain medications can trigger a lupus-like syndrome in people who would not otherwise develop the disease. The two drugs with the highest documented risk are hydralazine (used for high blood pressure) and procainamide (used for irregular heart rhythms). Both work by inhibiting DNA methylation in T cells, the same epigenetic disruption seen in spontaneous lupus.
Other well-established culprits include isoniazid (a tuberculosis drug), minocycline (an antibiotic), and quinidine (another heart rhythm medication). A class of drugs called TNF inhibitors, used to treat rheumatoid arthritis and other autoimmune conditions, has also been linked to lupus-like symptoms. In a large international pharmacovigilance database, more than half of drug-induced lupus cases were classified as serious.
Drug-induced lupus typically resolves within weeks to months after stopping the medication, which distinguishes it from the spontaneous form of the disease.
The Gut Microbiome Connection
People with lupus consistently show imbalances in their gut bacteria compared to healthy individuals, with reduced diversity and a shift in the ratio of major bacterial groups. One species in particular, Ruminococcus gnavus, appears to proliferate in lupus patients. Blood levels of antibodies against this bacterium correlate with disease activity scores and levels of anti-DNA autoantibodies.
The proposed mechanism centers on intestinal barrier integrity. In lupus, the gut lining becomes more permeable, a condition sometimes called “leaky gut.” Bacteria and their byproducts slip through the weakened barrier and enter the bloodstream. Some bacterial proteins structurally resemble human proteins, triggering the same molecular mimicry seen with EBV. Bacteria also form protective structures called biofilms that contain a protein associated with autoantibody production. These gut microbiome imbalances in lupus also appear to differ between men and women, suggesting that sex hormones influence both the composition of gut bacteria and their downstream effects on immune function.
Who Is Most at Risk
Lupus risk concentrates in specific populations. Women of childbearing age carry the greatest burden, particularly those of Black, Hispanic, Asian, or American Indian/Alaska Native descent. Black and American Indian/Alaska Native women face two to three times the risk of white women, a disparity driven by both genetic factors and social determinants of health including access to early diagnosis and treatment.
Having a first-degree relative with lupus significantly increases your risk, though most people with a family history never develop the disease. The interplay matters more than any single factor: a person might carry high-risk HLA gene variants, encounter EBV during adolescence, spend significant time in the sun, and experience hormonal changes during pregnancy, with each layer compounding the others until the immune system crosses a threshold it cannot return from on its own.