Physiology of the vellus hair follicle: hair growth and sebum excretion.

The growth of vellus hair and the secretion of sebum from vellus hair follicles were measured on the forehead, cheek, chest, shoulder and back of healthy men and women aged 15-30 years. Hair growth was assessed by computerized image-analysis of photographs and sebum excretion by the use of Sebutape followed by image analysis. The density of vellus hairs and the percentage of growing hairs were higher on the face than on the thorax (439 hairs/cm2 with 49% growing hairs on the forehead compared with 85 hairs/cm2 with 31.5% growing hairs on the back). The rate of growth ranged from 0.03 mm/day on the forehead to 0.13 mm/day on the back. The maximum length of vellus hair significantly decreased with age; otherwise hair growth was not affected by age or sex. Some variations in hair growth and sebum secretion were observed over a period of 3 months, but no consistent rhythms were detected. There was no obvious link between vellus hair growth and sebum excretion.