During the hair growth cycle, sections of hair go through the same phase simultaneously thus, leading to bald patches.
MYTH. Each hair follicle goes through the three different stages of hair growth independently, at individual paces. One strand may be in the anagen or growing phase while another may be in the catagen or transitional stage. Normally, 85% to 90% of the hair follicles are in the anagen phase, 3% are in catagen, and about 10% to 15% are in the telogen or resting phase. When the scalp loses sections or patches of hair at the same time, consult a dermatologist or hair expert immediately.