1. Medulla: This is the innermost core of the hair shaft. It is not always present, especially in fine or blonde hair.
2. Cortex: This is the middle layer and the thickest. It contains the pigment (melanin) that gives hair its color and is responsible for the hair's strength, elasticity, and texture.
3. Cuticle: This is the outermost layer, composed of overlapping scales that protect the cortex.
So, the layers of the hair shaft begin with the medulla.