Knot in hair

Photomacrograph of a knot in human hair. The hair shaft is made up of several layers of a tough protein called keratin. The outer layer (cuticle) is visible here and is made up of overlapping, tightly packed scales. Natural hair colour is determined by two types of melanin, pigments produced by melanocytes in the hair follicle. Eumelanin is black or brown in colour while phaeomelanin is red/yellow, and different proportions of these two pigments create the variety of shades of hair colour. Width of image is 3 cm.