The lack of significant changes in scalp hair follicle density with advancing age

Age-related reduction in hair is seen in the axillary and pubic regions as well as the scalp; however, it has not been investigated qualitatively on the scalp. Horizontally sectioned scalp biopsy is an ideal tool to investigate the impact of advancing age on scalp hair follicle density and morphology.

To examine the effect of age and follicle miniaturization on total hair count in 1666 horizontally sectioned mid-scalp biopsies from 928 women aged between 13 and 84 years with hair loss.

Specialist hair loss referral clinic in a teaching hospital.

Analysis of data set. Methods: All scalp biopsies were 4 mm in diameter and taken from the crown. Miniaturization was assessed by calculating the ratio of terminal to vellus-like hairs (T/V) at the mid-isthmus level and considered significant if the ratio was < or = 4 : 1. Fibrosis was documented when present. Linear regression was used to examine the association between total hair count, age and miniaturization.

The average number of hair follicles per biopsy was 39.6 (SD +/- 10.8). A highly significant negative association (P < 0.0001) was found between age and total follicle number, although the predictive value of age in total hair count was found to be small [root error mean square (R2) < 2%]. Controlling for T/V < or = 4 : 1, the association was weakened, but remained significant. The relationship unconfounded by T/V < or = 4 : 1 shows that for every additional year of ageing, 0.077 total hair follicles (0.22%) are lost per biopsy.

Age and follicular miniaturization were found to be extremely weak predictors of total hair count in women with hair loss.