When internal organs are involved, the condition is called systemic lupus erythematosus. The disease can affect all ages, but most commonly begins from age 20 to 45 years. It is more frequent in African-Americans and people of Chinese and Japanese descent. Factors which activate autoimmune disturbances that cause lupus are not known. Genetics, viruses, ultraviolet light, and drugs may all play some role.
Genetic factors increase the tendency of developing autoimmune diseases.
Autoimmune diseases such as lupus, rheumatoid arthritis, and thyroid disorders are more common among relatives of patients with lupus than the general population. Some scientists postulate that the immune system in lupus patients is more easily activated 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. It is also known that women patients with systemic lupus not infrequently experience worsening of symptoms prior to their menstrual periods. This phenomenon, together with the female predominance of those with the disease, suggest that female hormones play an integral role in the expression of systemic lupus.