Background: Few biological data on human eyelash follicles have been reported in the literature.
Objectives: To characterize eyelash follicle growth, cycle and morphology, and further investigate the biological mechanisms that determine eyelash length, curl and pigmentation, compared with scalp hair follicle.
Methods: Twenty-nine caucasian female volunteers aged between 26 and 60 years were enrolled in the study to provide eyelashes. Four of these volunteers were followed weekly for 9 months to characterize their eyelash cycle. Eyelash length and time of renewal were measured using a high-resolution camera and image analysis. Immunohistological study of the bulbs were performed on eyelid biopsies from 17 patients requiring block excision for ectropion repair.
Results: The calculated durations of anagen phase and complete cycle of the eyelashes were 34 + or - 9 and 90 + or - 5 days, respectively. Eyelash follicle growth rate was quite variable, with an average rate of 0.12 + or - 0.05 mm daily. Eyelash follicle morphology was very close to that of the scalp hair follicle, but some remarkable differences were noticed. For example, the K19-positive epithelial stem cell population was spread all along the follicle and not split into two reservoirs as seen in scalp hair follicles. Some asymmetry was detected in HSPG and CSPG, as well as K38 (formerly Ha8) and K82 (formerly Hb2) distribution, similar to that observed in curly hair. Finally, dopachrome tautomerase was found expressed in eyelash follicle melanocytes, while it was strikingly absent in scalp hair follicle melanocytes.
Conclusions: The eyelash is structurally very close to curly hair but some biological processes related to follicle cycle and pigmentation differ markedly.