Of the fifty million Americans affected by one or more autoimmune disease, 75% are women. In particular, they affect women of working age and during their childbearing years. No one knows why autoimmune diseases target females. Hormones are a plausible explanation, but the link between estrogen and disease is not clear.

Some autoimmune diseases occur more frequently in certain minority populations. For example, lupus is more common in African-American women than in Caucasian women of European ancestry. Rheumatoid arthritis and scleroderma affect a higher percentage of residents in some Native American communities than in the general U.S. population. These diseases are characterized by their elusive and unpredictable nature, and many are difficult to diagnose and treat.

While the outward appearance and functioning of the patient may be "normal", their quality of life is actually affected considerably. Certain diseases such as psoriasis can develop in different related individuals, and family members may even develop different autoimmune diseases caused by the same inherited and shared set of abnormal genes. For example, one first cousin may have lupus, another may have dermatomyositis, and one of their mothers may have rheumatoid arthritis. Many of the diseases that fall under this definition are not familiar to the average person. For example, Sjogren's Syndrome, a curious ailment that deprives the body of vital moisture, is one of the most prevalent autoimmune disorders, striking as many as 4 million Americans, nine out of ten of them being female.