The advice to brush hair 100 strokes daily as a hair health practice traces to Victorian-era beauty manuals and has persisted in popular wellness content despite minimal scientific support. The proposed mechanism involves improved scalp circulation and distribution of natural sebum along the hair shaft. The reality is somewhat more nuanced and considerably less dramatic than the folklore suggests.

Scalp circulation does respond to mechanical stimulation, this is documented in laser Doppler studies. But the effect duration is brief (minutes), the magnitude is modest, and there's no evidence that transient circulation increases translate to meaningful hair growth outcomes. The mechanotransduction studies that support scalp massage involve more substantial pressure than passive brushing produces. Excessive brushing, particularly of wet or fragile hair, causes hair shaft damage and breakage that outweighs any circulation benefit.

Practical guidance: gentle brushing serves cosmetic purposes (detangling, sebum distribution along the shaft) but isn't a hair loss treatment. Avoid aggressive brushing of wet hair, which is particularly fragile. Boar bristle brushes distribute sebum more effectively than synthetic brushes. The 100-stroke recommendation has no specific evidence base, brush as needed for styling without excess. Don't invest in expensive boar bristle brushes expecting hair regrowth; invest the same money in evidence-based treatments if that's the goal.