What causes lupus?

The precise reason for the abnormal autoimmunity that causes lupus is not known. Inherited genes, viruses, ultraviolet light, and drugs may all play some role. Genetic factors increase the tendency of developing autoimmune diseases, and autoimmune diseases such as lupus, rheumatoid arthritis , and immune thyroid disorders are more common among relatives of patients with lupus than the general population. Some scientists believe that the immune system in lupus is more easily stimulated by external factors like viruses or ultraviolet light. Sometimes, symptoms of lupus can be precipitated or aggravated by only a brief period of sun exposure.

Dozens of medications have been reported to trigger SLE; however, more than 90% of this "drug-induced lupus" occurs as a side effect of one of the following six drugs: hydralazine (used for high blood pressure), quinidine and procainamide (used for abnormal heart rhythm), phenytoin (used forepilepsy), isoniazide (used fortuberculosis), d- penicillamine (used for rheumatoid arthritis). These drugs are known to stimulate the immune system and cause SLE. Fortunately, drug-induced SLE is infrequent (accounting for less than 5% of SLE among all patients with SLE) and usually resolves when the medications are discontinued.

It also is known that some women with SLE can experience worsening of their symptoms prior to their menstrual periods. This phenomenon, together with the female predominance of SLE, suggest that female hormones play an important role in the expression of SLE. This hormonal relationship is an active area of ongoing study by scientists.