Variation in hair thickness across the scalp, often used as a trichoscopic clue to pattern hair loss.
Hair shaft diameter diversity means neighbouring hairs have noticeably different thicknesses. In androgenetic alopecia, terminal hairs progressively miniaturise, so a mixture of thick, intermediate and fine hairs appears in affected areas. This is different from pure telogen effluvium, where hair diameter is usually more uniform. Trichoscopy uses this pattern, alongside distribution, vellus hairs and follicular unit changes, to support the diagnosis and monitor progression or response to treatment.
DermNet trichoscopy of generalised non-cicatricial hair loss: https://dermnetnz.org/topics/trichoscopy-of-generalised-noncicatricial-hair-loss ; Starace et al., Am J Clin Dermatol 2020: https://doi.org/10.1007/s40257-019-00479-x