In her new Billboard cover story, Selena Gomez revealed that prior to a stint in rehab, she was diagnosed with the autoimmune disease lupus and had been through chemotherapy.
But what is lupus? A complicated autoimmune disease affecting 1.5 million Americans, according to the Lupus Foundation of America, lupus is most prevalent among women of childbearing age (15-44) and disproportionately affects women of color. When something goes wrong, sufferers' immune systems often attack healthy tissues and cells.