Which part of the hair contains cells that are actively reproducing?

The papilla is a structure located at the base of the hair follicle that contains blood vessels supplying nutrients to the hair. While it plays a vital role in supporting hair growth, it does not contain actively reproducing cells; rather, it nourishes the matrix, which is responsible for cell division.

The follicle is the entire structure that houses the hair, including various parts such as the matrix, papilla, and outer layers. Although it encompasses areas where cell proliferation occurs, the follicle itself is not the specific site of active cell reproduction; that role is designated to the matrix.

The root of the hair refers to the portion of the hair that is embedded in the follicle. While the root includes the matrix and the papilla, it is not the active site of cell division. The term "root" is more general and does not specify the region where reproduction takes place.