The rounded base of a hair follicle, where new hair cells are produced by rapidly dividing matrix cells.
Structure
The hair bulb surrounds a connective tissue projection called the dermal papilla, which supplies blood vessels and signals that drive matrix cells to divide.
Function
Matrix cells divide rapidly to push older cells upward, where they keratinize and form the visible hair shaft. Melanocytes near the dermal papilla add pigment to each new hair.
Clinical note
Damage to the dermal papilla in the hair bulb during chemotherapy or radiation interrupts cell division and causes the rapid hair loss seen with these treatments.
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