Hair Growth Cycle
The hair growth cycle consists of anagen, catagen, and telogen phases that regulate how hair grows, rests, and sheds. Understanding this cycle explains normal shedding, delayed regrowth after hair transplant surgery, and why visible results develop gradually over time.
Every follicle runs its own clock. Hairs do not cycle together, which is why humans shed continuously instead of moulting. At any moment a scalp holds hairs in three different states, and roughly 10 to 15 per cent of them are resting rather than growing (Hoover, Alhajj & Flores, Physiology, Hair, StatPearls).
| Phase | What happens | What it determines |
|---|---|---|
| Anagen | Active growth, lasting years on the scalp | Maximum length the hair can reach |
| Catagen | Brief transition; the follicle regresses | End of that growth run |
| Telogen | Rest, then the hair is released | Normal daily shedding |
Anagen length is the reason hair on different parts of the body stops at different lengths. Scalp anagen runs for years; on the body it is far shorter, so those hairs reach a few centimetres and let go. The follicle is not weaker — its growth run is simply shorter, and that limit travels with it if it is moved.
Surgery pushes grafts into the cycle deliberately. The trauma of being moved sends a transplanted follicle into rest, so the visible hair is shed within the first weeks. That shedding is the cycle working, not a failure. New growth appears when the follicle re-enters anagen, which is why nothing about a result can be judged in the first months.
Related terms
For the month-by-month course after surgery, see hair transplant growth stages. For how pattern loss is staged, see the Norwood scale.
