Hair Fundamentals


Getting to the root of hair care 


Hair is an amazingly complex biological structure forming the outer covering of most mammals. Hair fibers serve not only a functional role by providing a barrier between mammal and environment but one that also reflects history, culture, and personal choice.
Science has spent decades developing an in depth understanding of the human hair fiber: how it grows, why it behaves the way it does and how it interacts with the environment around it. Studies have mostly focused on the hair’s color – how it is affected by heat, UV light and chemical processing. Much of this focus is aimed at understanding how cosmetic products can better treat the hair and how we can improve upon them in support of a global multi-billion dollar market (almost $81 billion as of 2016).
Hair is predominantly constructed of a protein called keratin. Making up the balance of the fibers are small amounts of protein-bound sulfur, lipids, sugars, and minerals. The structure of the human hair shaft consists of three basic yet complex parts: the follicle, the cuticle and the cortex.
Our hair growth begins in a very intricate structure called the follicle located just below the surface of the scalp. It is here where the hairs’ shape and color are defined as the fiber is biosynthesized. Upon emerging from the follicle, the fiber is, for all intents and purposes, dead.
The cuticle forms the outer layer of each fiber manifested as thin overlapping sheets much like the shingles on a roof. The average fiber contains anywhere from six to 10 layers of cuticle. As the outer surface the cuticle makes up a minor proportion of the overall fiber – approximately 25 percent, it is often considered the most important due to its direct interaction with cosmetic treatments.
The cortex consists of longitudinal cells forming the inner structure of the fiber making up almost 75 percent of the fiber mass. Cortical cells run parallel to the fiber axis and are protected by the cuticle. The cortex is very complex and provides the hair fiber with most of its mechanical strength. Embedded in the cortex are melanin granules which give rise to the color of the fiber. The natural color of all human hair is derived from two types of melanin: Eumelanin which is responsible for the black/brown colors and Pheomelanin which provides red coloration. Each particular color is the result of the amount and type of melanin distributed through the hair fiber.
The medulla, when present, makes up a very tiny portion of the innermost region of the fiber defined as a loosely packed porous region. The role of the medulla is not well understood. The presence of a medulla and its pattern can vary greatly person to person and amongst fibers on any individual’s head. One fiber may have a fragmented medulla while the next completely devoid of one.
As discussed, hair fibers are formed in the follicle where they grow in a three-phase cycle. Each individual hair fiber grows in an active phase called Anagen, then passing into a transitional or recession stage called Catagen, followed by a resting phase called Telogen. The typical length of the Anagen stage is 3-5 years. We also know that all human hair grows at a rate of 0.5 inches per month (or 6 inches per year). Simple math tells us that the average human is capable of growing hair about 30 inches in length. As a follicle transitions through these phases, it becomes a normal event to shed the fiber. We, as humans, typically shed about 100 hairs a day.
The preceding only scratches the surface of the topic of human hair. We continue to explore, learn, and understand this complex structure and its behavior.

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Meet Peter Rousso
Peter Rousso, Vice President of R&D
Peter has been a part of the Beauty industry for over 34 years. He has also worked for companies, such as Clairol, P&G, Conair and Avon.