Editor's Note: At MODERN SALON, we’re celebrating101 yearsof educating and inspiring beauty professionals. As part of this milestone, we’re embracing the concept of "101" courses--those introductory courses in the U.S., where the first level of any subject is often numbered 101 (e.g., "Biology 101" or "Marketing 101"). These courses cover the fundamentals, providing a foundation of essential knowledge before diving into more advanced topics. 

In that spirit, we’re sharing this refresher on the Anatomy of Hair written by Tej Belagodu because no matter how long you’ve been working at your craft, the fundamentals are always worth revisiting.

HAIR SCIENCE 101: THE ANATOMY OF HAIR

Whether you're a hairstylist, a salon owner, or in a corporate role; if you're a part of the beauty industry, you understand the importance of hair to an individual – the delight of a good hair day, the anxiety of thinning hair, and everything in between. Regardless of your specialty in the hair industry, here's a quick refresher on the anatomy and biological structure of hair.

Hair is primarily composed of a protein called keratin. Long, coiled chains of this protein are linked end-to-end and arranged in a spiral structure called a helix to form hair strands. The elements that make up this protein are carbon, oxygen, nitrogen, hydrogen, and sulfur, in that order. Interestingly, these are the same elements that make up skin and nails.

Broadly, a mature strand of hair is composed of two parts: the hair root, which is below the surface of the skin/scalp, and the hair shaft, which is above it. The follicle generates living cells which transform into protein as they mature and move upwards toward the surface of the skin. As they emerge and become a part of the hair shaft, they are completely keratinized, have lost their nucleus, and are no longer living cells.

Things get a little more interesting when you look at the cross-section of a strand of hair (Image 1). Each strand is composed of three distinct layers: the medulla (innermost), the cortex (middle), and the cuticle (outer). Their composition, thickness, and characteristics can vary greatly from person to person. The medulla typically does not participate in salon services and is often completely absent in fine hair. The bulk of the weight of hair strands comes from the cortex which can be accessed by lifting the cuticle layer using an alkaline solution. The cuticle has a scaly structure and typically bears most of the brunt of styling, coloring, products, and the elements. 

Image 1. Cross-section of a hair strand. 

Credit: Tej Belagodu

The cuticle arguably plays the biggest role in how your hair looks and feels, and consequently, it is the layer talked about the most. Damaged or unhealthy cuticles lead to a loss of shine, frizz, unmanageable hair, and can even lead to split ends. A variety of reasons can cause harm to cuticles, but the most common ones are harsh chemical treatments, frequent use of hot tools, and mechanical stress to hair (think vigorous brushing, tight ponytails, etc.). Damaged cuticles can be nursed back to good health, however. Moisturizing and conditioning, gentle sulfate-free hair care products, heat protection, scalp massages, and periodic hair masks can all help. Additionally, a vital tip that works wonders on the cuticle is to do a cold rinse at the end of a hair wash. The cold water makes cuticles lay down flat, giving hair shine as well as preventing moisture and dust from entering the shaft (Image 2).

Image 2. Electron microscope image of the author’s hair strand. The scaly surface is the cuticle.  

Credit: Tej Belagodu

As for the cortex and medulla, a balanced diet with healthy proteins and the right amounts of micronutrients like vitamins A, C, D, and E, amino acids, biotin, and omega-3 fatty acids go a long way. Good practices suggested here previously, like avoiding harsh chemicals, minimal heat styling, and scalp massages, help promote healthy cortex and medulla layers as well. Additionally, regular trims are highly recommended to keep hair pruned and growing healthily. Trims help prevent split ends, or at a minimum, prevent them from going deeper into the hair shaft and compromising the integrity of the inner layers.

So there! That's the biology of hair in a nutshell, along with simple tips to keep your hair healthy.

ABOUT THE AUTHOR: Tej Belagodu is a hair enthusiast and entrepreneur. During the Covid19 pandemic, he developed an online marketplace where clients could buy customized DIY hair color kits formulated by licensed stylists based on a video consultation. He is currently exploring a couple of new ideas in the hair industry and evaluating their viability. Occasionally, he writes articles on various topics related to hair. At his day job, he is an Engineering Manager in the manufacturing organization of a semiconductor technology company. He has a Master of Science degree in Electrical Engineering from Arizona State University. Tej can be reached at tej.belagodu@gmail.com.