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RO Depth is set against the graft, not against a number. There is no universal millimetre figure. The channel has to match the length of the follicular units being placed, and those differ between donors and between grafts in the same donor. Depth is calibrated on the first sites, with real grafts, and rechecked as the scalp changes thickness across the head.
| Channel | What follows |
|---|---|
| Too shallow | The graft sits proud, dries out, and lifts out of the site — popping |
| Correct | The graft sits flush, anchored, its bulb in contact with living tissue |
| Too deep | The graft is buried — pitting, trapped hair and cysts |
Both errors damage growth, by different routes. A shallow graft loses contact with the tissue that has to supply it before new vessels reach it. A buried graft is surrounded by skin that closes over it, so the hair grows into a depression or fails to surface at all. Neither shows on the day; both show at the end of the growth phase.
Depth is also where the recipient area is protected. Channels that go beyond what the graft needs reach the vascular layer that will keep every surrounding graft alive. Restraint here is not caution for its own sake — it is what stops one row of sites compromising the blood supply of the whole area.
Related terms
For raised or uneven healing over the sites, see cobblestoning after a hair transplant. For the implantation stage in context, see the DHI technique.
