First of all "alopecia" really just means hair loss, and obviously, that refers to anyone who experiences it. For most people, it can be attributed to another cause (severe obesity, chemotherapy, genetic traits), but it appears to be more common in black women who don't otherwise have the usual physiological factors. The causes of it are not fully known yet, but it's a well known fact in the African American community that women run a heightened risk of losing their hair for no discernible reason.