what causes alopecia areata
1 This could be due to pregnancy, childbirth or the onset of menopause. Hormone levels are also affected by the thyroid gland, so thyroid problems may cause hair loss.  Patchy hair loss. This type of nonscarring hair loss is called alopecia areata (al-o-PEE-she-uh ar-e-A-tuh). It occurs when the body's immune system attacks hair follicles â causing sudden hair loss that leaves smooth, roundish bald patches on the skin.