You are born with every hair follicle you will ever have.

The development of hair follicles is a complex embryonic process that begins around the ninth week of gestation. By the 22nd week, a fetus has approximately 5 million hair follicles across the entire body, with about 100,000 of those located on the scalp. This total number is fixed for life because the specialized stem cells required to create new follicles are only active during fetal development.According to the American Academy of Dermatology, humans do not generate any new hair follicles after birth. As an individual grows from an infant into an adult, the surface area of their skin increases significantly. Because the number of follicles remains constant, the density of hair per square inch naturally decreases over time.Research published in the Journal of Investigative Dermatology highlights that hair thinning is often a result of follicle miniaturization rather than the loss of the follicles themselves. However, if a follicle is destroyed by scarring or physical trauma, the body cannot replace it. This is why conditions like cicatricial alopecia lead to permanent hair loss, as the biological machinery to build a new follicle is no longer present.Modern regenerative medicine is currently investigating ways to 'wake up' dormant cells or use 3D bioprinting to create new follicles. However, as of now, natural human biology remains limited to the initial set provided at birth. This biological constraint is a primary reason why hair transplants involve moving existing follicles from one area to another rather than growing new ones from scratch.