Alopecia is, simply put, hair loss. If you have alopecia, you might see extra hair on pillows or in shower drains, or you might notice bald patches on your scalp. Over time hair loss can grow back or fall out permanently, depending on the cause. Alopecia is not curable, but it's treatable and not life-threatening.
Alopecia areata describes hair loss to a particular area. It has different levels of severity, so there might be just a coin-sized area of hair loss on the scalp, or it could affect large areas. It can occur anyplace on the body.
Or, it might result in complete hair loss on the scalp, alopecia totalis. Some people lose eyebrows or see a thinning of their eyelashes.
People can even have alopecia universalis, which is a loss of hair on the entire body.
Alopecia areata is considered an “immune-mediated” type of hair loss. The immune system is attacking the hair follicles. It has to do with T cells, the important white blood cells in the immune system.