Systemic lupus erythematosus (SLE), also known simply as lupus, is an autoimmune disease in which the body's immune system mistakenly attacks healthy tissue in many parts of the body. Symptoms vary between people and may be mild to severe. Common symptoms include painful and swollen joints, fever, chest pain, hair loss, mouth ulcers, swollen lymph nodes, feeling tired, and a red rash which is most commonly on the face. Often there are periods of illness, called flares, and periods of remission during which there are few symptoms.The cause of SLE is not clear. It is thought to involve genetics together with environmental factors. Among identical twins, if one is affected there is a 24% chance the other one will be as well. Female sex hormones, sunlight, smoking, vitamin D deficiency, and certain infections, are also believed to increase the risk. The mechanism involves an immune response by autoantibodies against a person's own tissues. These are most commonly anti-nuclear antibodies and they result in inflammation. Diagnosis can be difficult and is based on a combination of symptoms and laboratory tests. There are a number of other kinds of lupus erythematosus including discoid lupus erythematosus, neonatal lupus, and subacute cutaneous lupus erythematosus.There is no cure for SLE. Treatments may include NSAIDs, corticosteroids, immunosuppressants, hydroxychloroquine, and methotrexate. Alternative medicine has not been shown to affect the disease. Life expectancy is lower among people with SLE. SLE significantly increases the risk of cardiovascular disease with this being the most common cause of death. With modern treatment about 80% of those affected survive more than 15 years. Women with lupus have pregnancies that are higher risk but are mostly successful.Rate of SLE varies between countries from 20 to 70 per 100,000. Women of childbearing age are affected about nine times more often than men. While it most commonly begins between the ages of 15 and 45, a wide range of ages can be affected. Those of African, Caribbean, and Chinese descent are at higher risk than white people. Rates of disease in the developing world are unclear. Lupus is Latin for "wolf": the disease was so-named in the 13th century as the rash was thought to appear like a wolf's bite.