Hair growth is determined by which process in the hair follicle?

• A. Melanin production in melanocytes
• B. Desquamation of keratinocytes
• C. Protein synthesis in the dermis
• D. Cell division in the follicle

Answer: (D)

Hair growth is driven by cell division in the hair follicle’s matrix. The matrix cells divide rapidly and then keratinize to form the hair shaft, pushing it upward and lengthening the strand. The rate and duration of this mitotic activity—the anagen phase—determine how quickly hair grows. Melanin production in melanocytes affects hair color but not the growth rate. Desquamation of keratinocytes relates to shedding, not the main buildup of the hair shaft. Protein synthesis in the dermis supports surrounding tissues but does not directly drive hair shaft formation. Signals from the dermal papilla stimulate matrix cell division, making follicular cell proliferation the key process.