These lyrics from the popular Broadway musical Hair are humorous, but they do raise a very serious question: what exactly is hair? Simply put, the answer is that hair is protein. This simple answer, however, does not even begin to explain the complexity and sophistication of the hair fiber.
Science is like that sometimes; it starts with a simplistic model that evolves to explain more subtle and complex details. For example, consider how the conception of the atom has evolved over time. The ancient Greeks originally described atoms as simple, tiny, indivisible particles. This notion was expanded on by Bohr’s theory that atoms were more like miniature solar systems with electron “planets” revolving around a “solar” nucleus. Other theories have evolved to the point where atomic structure now is viewed as an electron density cloud swirling around a diverse collection of subatomic particles.
The concept of hair biology has gone through a similar evolution. The simplistic view that “hair is made of protein” has been replaced by a more detailed picture of the three structural components of hair: the cuticle, the cortex and the medulla. This three-component model has evolved even further to include a variety of substructures. This article will begin with a review of the basic components of hair and then describe the current understanding of its more complex physical and chemical substructure.
By gaining a greater understanding of the complex structure of hair, cosmetic chemists should be able to identify new targets for improving current products and maybe even create whole new product categories.