Normal Head-Hair Length Is Correlated With Its Diameter

In 2004, a study involving 25 young women found a correlation between the length and diameter of head hair, challenging previous assumptions about hair growth and miniaturization in conditions like androgenetic alopecia (AGA). The study revealed that hair diameter increases rapidly to a maximum at about 25% of the hair's total potential length and then decreases, with the rate of diameter increase being statistically significant. It introduced a new class of normal hair (EA) with both exogen clubs and anagen tips, suggesting that hair length variability is normal and that the concept of hair miniaturization in AGA should be revised. The study also indicated that hair diameter could be a useful biological indicator of disease and physiological function, but that current estimates of its variability may be significantly overestimated.