Around the papilla is the hair matrix, a collection of epithelial cells often mixed with the pigment-producing (color) cells, known as melanocytes. Cell division in the hair matrix is responsible for the cells that will form the major structures of the hair fiber and the inner root sheath. The hair matrix epithelium is one of the fastest-growing cell areas in the human body, which is why some forms of chemotherapy which kill dividing cells or radiotherapy may lead to temporary hair loss. The papilla is usually oval or pear-shaped, with the matrix wrapped almost totally around it, except for a short stalk-like connection to the surrounding connective tissue that provides access for the capillary.