Why hair is slower than almost anything else
Each hair spends years in a growing phase, then rests for roughly three months before it falls and a new one starts. Because of that delay, the hair you are losing today often reflects something that happened to your body two or three months ago: a fever or infection, childbirth, surgery, a crash diet or a period of intense stress.
The same delay works in the other direction. Whatever changes now — treatment, nutrition, a hormone level coming back into range — takes months to show on your head. Losing somewhere around 50 to 100 hairs a day is considered normal, so the question is always whether shedding is clearly above your own usual.