Hair density, hair diameter and the prevalence of female pattern hair loss

Background Female pattern hair loss is common but Estimates of its prevalen ce have varied widely. The relationships between the clinical diagnosis of female pattern hair loss and objective measurements of hair density and hai r diameter have not previously been evaluated. Objectives To determine the prevalence of female pattern hair loss and to r elate the clinical findings to hair density and hair diameter. Methods We examined 377 women, aged 18-99 years, who presented to a general dermatology clinic with complaints unrelated to hair growth (the unselecte d sample). A second group of 47 women referred with typical female pattern hair loss was included in analyses of the relationships between hair densit y, hair diameter and the clinical diagnosis. Hair density was measured usin g a photographic method, In each subject the major and minor axis diameters were measured in a random sample of 50 hairs. Results Six per cent of women aged under 50 gears were diagnosed as having female pattern hair loss, increasing to 38% in subjects aged 70 years and o ver, The mean +/- SEM hair density was 293 +/- 61.3 hairs cm(-2) at age 35 years, falling to 211 +/- 55.1 hairs cm(-2) at age 70 years, Hair density s howed a normal distribution in the unselected sample. Most women classified as having female pattern hair loss had hair densities within the lower hal f of the normal distribution. The perception of hair loss was determined ma inly by low hair density (ANOVA P < 0.001), but there was overlap in hair d ensity between women classified as having Ludwig I hair loss and the no hai r loss group, which was partly accounted for by differences in mean hair di ameter (ANOVA P < 0.001). Low hair density was associated with fewer hairs of all diameters. Conclusions Hair density in women is distributed as a normal variable, indi cating that it is determined as a multifactorial trait. Women with female p attern hair loss have a hair density which falls below the mean but lies wi thin the spectrum of the normal distribution, although other factors, inclu ding hair diameter, may affect the subjective impression of hair loss. The hair diameter data suggest that low hair density is not due to progressive diminution in hair follicle size and that follicular miniaturization may oc cur within the space of a single hair cycle.