What is Alopecia Areata, a condition that Will’s wife Jada suffers from?

Actor Will Smith had slapped comedian Chris Rock after the latter joked about his wife's condition during the Oscars. Jada Pinkett Smith suffers from Alopecia Areata, where the immune system attacks hair follicles and causes hair loss. Individuals with the disorder might experience slow or rapid hair fall in small, round patches. There is no cure for Alopecia so far.