Every follicle runs its own clock: years growing a hair, then three months resting before the next growth phase pushes it out. Normally that release is staggered, so a healthy scalp sheds fifty to a hundred hairs a day ¹. A shock drives a large fraction into rest together, and three months later they let go on the same schedule, so the shed arrives in a clump ². The hair coming out is finished and on time. The shedding is the past arriving on a delay, not the present accelerating.

The trigger is almost always in the 90 days before it began. The postpartum drop is the cleanest case: two in five women shed visibly three to six months after delivery ³. COVID produced a textbook wave, onset around eight weeks after symptoms ⁴. Crash dieting, a new drug (or stopping the pill), and severe stress all qualify ⁵. Two causes are worth a blood test: an off thyroid, which drives diffuse shedding in both directions ⁶, and clearly low iron — though the biggest case-control study found no ferritin difference between chronic shedders and controls, so treat real deficiency but doubt the "push it over seventy for hair" target ⁷.

The timeline back, once the trigger has cleared:

• Weeks one to four: no change, still shedding.
• Months two to four: the count drops below its peak. You stop dreading the shower. Nobody else notices.
• Months four to six: short, dark, fine new hairs stand up along the hairline; the part stops widening ².
• Months nine to twelve: the brush comes out near empty, and the hair is the hair you had before ⁹.

If the shed lasts past six months, or is unmasking a pattern loss underneath, topical minoxidil 5% twice a day is the backstop; the extra shed it causes in the first weeks is it starting to work ¹⁰.