Alopecia areata, which is known to common man as spot baldness, is an autoimmune disease in which hair is lost from some or all areas of the body. The science involved simply put is the inability of the white blood cells to properly recognize host cells and disease cells and attack the host cells and in the process it thinks the hair follicles are foreign particles and it wrongly recognizes them as a threat and attacks them leading to their loss.
This is the exact condition which affected Raftaar. The rapper was bold enough to put out a photo of the successful surgery and went on to put out the following message :