Transplanted hairs shed between weeks two and eight in almost every patient, and some native hairs go with them. Here is what grows back, what does not, and when.
Nearly every transplanted hair falls out between the second and the eighth week, and the follicle underneath stays alive and regrows. The shaft is shed because the follicle enters a resting phase after being moved; the structure that produces hair is not lost. Separately, native hairs around the new channels can shed from the trauma of surgery. That second event is what people usually mean by shock loss, and it affects a minority of patients to a visible degree.
Shedding begins around week two, peaks between weeks four and six, and is finished by week ten. New growth starts at month three or four, is thin and fine at month six, and reaches full calibre between months twelve and eighteen. Month three is the low point: transplanted hairs gone, some native hairs shed, new growth not yet visible. Nothing has failed at month three, and no decision about revision should be taken anywhere near it.
Native hairs that shed are usually those already miniaturised by DHT and close to the end of their cycle. Most return within six months. A proportion that were already on their way out do not, and the surgery simply revealed a timetable that was already running. This is more common in the crown and in patients with diffuse thinning, and it is the main reason we prefer to start medical therapy before surgery rather than after, in men who are candidates for it.
Three things help and one does not. Placing channels between existing hairs rather than through them reduces native trauma. Medical therapy started before surgery stabilises the hairs most at risk. Avoiding heat, pressure and pulling for the first month protects what is left. What does not help is any lotion promising to stop the shedding, because the follicle is in a resting phase and nothing applied to the skin shortens that phase.
By the calendar. Shedding in the first two months with regrowth from month four is shock loss. A genuinely failed transplant leaves an area still bare at month twelve, with no fine hairs appearing at any point along the way.
In men with ongoing miniaturisation, starting about three months before surgery reduces native shedding and protects the hairs the transplant is built around. It is a decision to take with a doctor, not a default for everyone.