What is the innermost layer of the hair structure called?

The innermost layer of the hair structure is known as the medulla. This layer plays a crucial role in the overall makeup of the hair strand. The medulla is a soft, flexible core that may or may not be present in all types of hair, being more prominent in thicker or coarser hair types. Its presence can affect the hair's texture and quality, contributing to the overall characteristics of the hair. Understanding the structure of hair is essential in esthetics, especially when considering different hair types and their specific care requirements, as well as how products might interact with each layer of the hair. Other layers, such as the cuticle and cortex, have their own important functions, but they are not considered the innermost layer.