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RO These two words describe every hair on the body, and they are defined against each other. Terminal hair is thick, pigmented and long — scalp, beard, eyebrow. Vellus hair is the fine, short, near-colourless down that covers most of the rest of the skin. Both are present on every healthy scalp; what changes in hair loss is the ratio between them.
| Terminal hair | Vellus hair | |
|---|---|---|
| Shaft | Thick and pigmented | Fine, pale, around 0.03 mm or less |
| Length | Grows for years | Stops after a short run |
| Medulla | Usually present | Absent |
| Coverage | Blocks light, hides scalp | Effectively invisible |
Pattern loss is a conversion, not a disappearance. Follicles do not vanish in early androgenetic alopecia; terminal hairs are progressively replaced by finer ones until the area reads as bald while still carrying hundreds of follicles. Vellus hairs are found in the majority of patients examined under magnification for pattern loss (Kuczara et al., Journal of Clinical Medicine, 2024).
Only terminal hair is worth transplanting. A graft is judged by the hair it will produce, so vellus and near-vellus units are of no value in the recipient area — and a donor zone containing many of them is a donor zone that is already changing.
Related terms
For how a full scalp is graded once loss is visible, see the Norwood scale. For why thinning shows first on a wet scalp, see seeing your scalp when hair is wet.
