The cause of lupus is unknown. Scientists have proven that lupus is autoimmune in origin – in other words, the damage in lupus is caused by the body’s immune system attacking its own tissues – but they have not yet solved the puzzle of why this process begins.
While researchers have established that both hereditary and environmental factors influence a person’s risk for developing lupus, no one has identified why some people get lupus and some people don’t. Most scientists believe lupus is most likely caused by a combination of inherited and environmental factors.
It is important to note that while science is good at finding correlations, or apparent relationships, between factors and disease, correlation does not prove that the factor causes the disease. Many risk factors for lupus have been identified and are being studied, but none have been pinpointed as the cause of lupus.
Lupus does not appear to be directly inherited from parents in any clear genetic pattern. However, people with a close family member who has lupus have a higher chance for developing the disease themselves. An average person’s risk for developing lupus is .004 percent, or 1 in 250. If a parent has lupus, their child has a risk of approximately 5 percent of developing lupus. In identical twins, if one twin is diagnosed with lupus, the other twin has about a 25 percent chance of developing the condition. Risk for lupus also increases if one or more family members have other autoimmune diseases such as rheumatoid arthritis, Crohn’s disease, ulcerative colitis, or multiple sclerosis. Scientists have singled out more than 50 genetic variants that are more prevalent in those with lupus, but more research is needed to understand hereditary predisposition for lupus.
Women are nine times more likely than men to develop lupus. In general, autoimmune diseases strike women at much higher proportions than men. In the U.S., 75 percent of those with an autoimmune disease are women. Women’s immune systems are believed to be more effective than men’s, giving women greater protection from infections, but making them more vulnerable to autoimmune disorders. Hormones such as estrogen, which women produce in much higher proportion than men, may also influence the risk for developing lupus. In many women, lupus tends to flare during menstruation and pregnancy, when hormone levels are highest.
Ethnicity also influences lupus predisposition. People of African, Asian, Native American, Latin American, and Pacific islander descent have a significantly higher risk of developing lupus than people of European descent. African-American women are more than three times more likely to be diagnosed with lupus than Caucasian women. Research also indicates that people of different races may experience symptoms differently.
Researchers have identified a wide array of environmental factors linked to the development of multiple sclerosis. Several studies have investigated specific viruses for links with lupus. Some scientists believe that one or more common viruses such as the Epstein-Barr virus (the cause of mononucleosis, or “mono”), herpes zoster (responsible for chickenpox and shingles), or cytomegalovirus may cause genetic changes in some people, paving the way for the development of lupus.
Exposure to ultraviolet light (sunlight, fluorescent lights, tanning beds) is known to trigger lupus flares in many people, and some scientists theorize that it is part of what causes lupus to develop. Certain antibiotics increase photosensitivity (sensitivity to light) and may help pave the way for lupus development as well.
Similarly, physical and emotional stress are well-known flare triggers that some believe encourage lupus to develop. Many people experience their first lupus symptoms after stressful events such as a traumatic injury, giving birth, the death of a loved one, divorce, or surgery.
Another theory is that exposure to unspecified toxins or silica dust – a compound found in quartz rock and a common byproduct of many industries – triggers the development of lupus.