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Hair follicle miniaturization is a result of asymmetric cell division that occurs during the aging process; it can also be caused by certain genetic factors, psychogenic stress factors, and nutritional imbalances. Miniaturized hair follicles are then incapable of regenerating, leading to hair loss. Follicles are tiny organs that constantly facilitate growth of new hair via hair follicle stem cells (HFSCs). HFSCs undergo both symmetric and asymmetric cell division periodically. Symmetrical division produces two identical cells, each with the same fate. Asymmetric division produces one differentiated cell and one self-renewing stem cell that ensures the constant growth and survival of stem cell populations. How the previously mentioned factors contribute to the age-related loss of HFSC function is not fully understood. To maintain normal epidermal physiology, symmetrical and asymmetrical cell divisions should remain balanced, and proper hair follicle function is impacted if the stem cells preferentially go through one of these processes over the other. Age-associated repetition of hair cycles can cause sustained DNA damage responses in HFSCs, resulting in hemi-desmosomal instability, and causing repetition of atypical stem cell divisions that induce epidermal differentiation in HFSCs, eventually detaching these cells from the base membrane. HSFCs can become exhausted over time, leading to hair thinning and hair loss.
REFERENCES : Nature Aging. 2021 Feb; 1, 190–204. doi: 10.1038/s43587-021-00033-7
