Differences in hair follicle dermal papilla volume are due to extracellular matrix volume and cell number: Implications for the control of hair follicle size and androgen responses

The size of a hair follicle is thought to be determined by the volume of it s dermal papilla, The volume of the dermal papilla depends on the number of cells it contains and on the volume of the extracellular matrix. To establ ish which of these two variables is related to differences in hair follicle size we performed a stereologic study on 235 hair follicles from different sites, including male facial skin (beard), female facial skin, and scalp. In facial follicles there was a strong correlation between the area of the hair cortex and the volume of the dermal papilla, The area of the hair cort ex also correlated with the number of cells in the dermal papilla and with the volume of dermal papilla per cell. In scalp hair follicles, where there was a smaller range of sizes, the correlations between these variables wer e weaker. In large male facial follicles the mean total dermal papilla volu me was almost 10-fold higher than in vellus follicles from female facial sk in. This difference was associated with a mean 17-fold greater number of ce lls in the dermal papilla and a 2.4-fold greater volume associated with eac h cell. Intermediate results were obtained in scalp follicles, In many regi ons of the skin hair follicles enlarge in response to androgens during adul t life hair. Our results imply that the increase in the volume of the derma l papilla in these follicles is due to an increase in the number of cells, either through proliferation or through the migration of cells from the fol licular dermal sheath, and to an increase in the amount of extracellular ma trix per cell. As androgens are thought to act primarily on the dermal papi lla, these changes may have a direct bearing on the mechanism of androgen-m ediated alterations in hair follicle size.