What to Know About Hair Structure and Composition
Hair comes in such a gorgeous variety of shapes, sizes, colors and textures — straight to kinky, blond to black, thick to fine. Why does hair vary so much from person to person?
No matter what your mane looks like, the same basic biology applies when it comes to how your body produces hair. Before you groan at the thought of a science lesson, this is actually pretty important stuff to know when it comes to growing your healthiest possible hair and learning how to best care for it, too.
Read on to get all the foundational follicular knowledge you need to live your best hair life.
Your Scalp Is Like a Hair Farm
“The first basic fact to get on the table: The hair and the scalp are two different things,” said Dr. Erum Ilyas, a board-certified dermatologist and founder of Amber Noon. Even so, she acknowledged that the two are connected in a complex ecosystem that works harmoniously to produce your visible locks. “Think of your scalp like a farm. The scalp is the soil that grows a crop called hair,” Dr. Erum added.
What makes for a healthy scalp? Like soil, there are lots of factors at play to support scalp health. If the skin on your scalp is dry, flaky or irritated, then chances are your hair’s development will be impacted.
“If the scalp is not healthy, then the hair that grows from it cannot be either," said Dr. Iyas. "If there’s inflammation, itching or irritation, think of these issues as complications that can impact the way that your hair grows. It can make your hair grow out fine and wispy, or it can grow out damaged and easily breakable.”
How does the state of your scalp affect your hair, exactly? Here's more about the hair incubators that live on your scalp (and all over your body): follicles.
Discover: Why a Healthy Scalp Is Important for Healthy Hair
Follicles Are A Hair’s Best Friend
Follicles are where the hair magic happens. They are complex structures that live within the skin to produce the visible hair strands, or ‘shafts,’ on your head and body.
Hair follicles start developing in utero just weeks after conception. And once you’re born, you will have all the hair follicles you will ever have: Your body won’t produce more follicles as you grow. You have about 90,000-150,000 follicles on your head, and that number typically decreases with age. In fact, less than half of women go through life with a full head of hair.
How Hair Follicles Do Their Thing
Follicles are womb-shaped structures that live in the dermis, a layer of your skin. And just like any mammal’s womb, there is a lot going on inside your follicles to produce body hair and the hair you end up seeing on your head. The main structures of a hair follicle are:
- The hair bulb
- The hair root
- The hair shaft
The Hair Bulb
The hair bulb is, not surprisingly, a bulb-shaped structure at the base of the hair follicle. Dipping into the bottom of this bulb is the dermal papilla, which is a collection of nerve endings and blood vessels that deliver essential nutrients and oxygen to the hair matrix. The hair matrix is a system that produces the cells used to build the hair shaft. Melanocytes are the cells that determine hair color, and these cells are found in the hair matrix, too.
The Hair Root
The hair root is a larger structure that houses and oversees the continuing development of the hair shaft before it emerges from the skin. Here in the root, the cells produced in the hair matrix continue to divide, harden and eventually die in a process called keratinization. The dead cells pile on top of one another and fuse together, becoming organized into strong filaments, called keratin filaments. These filaments then become the various layers of the hair shaft (more on that later).
External to the hair follicle, there are two more important structures in hair anatomy:
- Arrector Pili Muscle: A small muscle that is attached to the hair follicle and responds to emotional distress or cold temperatures. By pulling on the hair follicle, it makes the hair stand up, producing goosebumps.
- Sebaceous Gland: A gland attached to each hair follicle that secretes sebum, an oily substance that conditions the hair and surrounding surface of the skin.
Given what you now know about follicles, it should make sense that products designed to support healthy hair growth, like our GRO Hair Foam or hair serums, will focus on nourishing the hair follicle (either topically or internally) since that is where hair creation takes place. It’s in the hair follicle that changes to your hair’s development, and growth cycles can be made. In other words, healthy follicles make for healthy hair shafts.
The Anatomy of the Hair Shaft
Hair shafts, or individual strands of hair, are made from keratin, which is a very durable and strong protein also found in your nails and in the claws, hoofs and feathers of animals.
Each hair, or shaft, is made up of several concentric layers, making its structure tube-like. These keratinized cells become organized into three layers to form the shaft:
- The medulla
- The cortex
- The cuticle
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The medulla is a soft and springy inner core that’s typically only found in the thickest of hair strands. It’s made up of transparent cells and pockets of air.
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The cortex is the bulk of each hair shaft. It’s made up of several layers of compressed cells that have been given color, or pigment, from the melanocytes located in the bulb. The properties of the cortex will determine the strength and texture of your hair, too. But the cortex isn’t infallible.
“A damaged cortex leads to split ends,” explained Dr. Sharleen St. Surin-Lord, board-certified dermatologist of Visage Dermatology. Not only that, but anytime you chemically treat your hair, the changes occur by manipulating the cortex. “It is the disulfide bonds of the cortex that are altered with chemical relaxers, bleaching, dyeing and perms,” she explained.
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The cuticle is the outermost layer of the hair shaft. It’s a thin layer of transparent keratinized cells, and “it also contains fatty acids, ceramides and cholesterol,” according to Dr. St. Surin-Lord.
The cuticle plays an important role in the shaft’s overall architecture. First off, the cuticle protects the cortex. It also regulates the movement of moisture in and out of the cortex, which is important for maintaining your hair’s hydration and flexibility.
The structure of the cuticle is similar to a shingled roof. In a healthy cuticle, the cells, or shingles, will lie smooth and flat. Chemical treatments, heat styling and even general wear and tear can damage the cuticle, lifting the cells up and exposing the cortex below. “When the cuticle layer is damaged, it causes frizz, dullness and breakage,” added Dr. St. Surin-Lord.
Also: What Is Hair Made Of?
Why Hair Has Different Textures, Types and Colors
The differences in hair type, hair texture and hair color result in all the glorious diversity we see sitting atop human heads. As you may have already guessed, the hair follicle has a role to play here.
When it comes to hair type (straight, wavy, curly and kinky), it’s actually the shape of the follicle that is the determining factor. Round follicles will produce straight hair, while oval follicles produce wavy hair and elliptical follicles produce curly and kinky hair.
Hair texture (fine, medium, coarse), on the other hand, has to do with the overall size of the follicle. Small follicles will produce a fine hair shaft, while large follicles produce a coarse (or thick) hair shaft. Follicles that fall in the middle produce hair shafts of medium thickness.
What about hair color? Melanocytes in the hair matrix produce melanin, which provides hair with its pigment or color. Genes determine the variety and amount of melanin each person produces, and melanin colors both your hair and your skin. There are two types of melanin: eumelanin and pheomelanin.
Eumelanin is what creates the black to blonde spectrum of pigment in hair. When follicles make a high concentration of eumelanin, hair color will be black. When there is a moderate amount, hair color will be brown. And when it is produced in small quantities, hair color will be blond.
Pheomelanin is what produces red pigment. A person's natural hair color is the result of different ratios of eumelanin and pheomelanin coming together to produce a unique hue. As you get older, your follicles gradually lose the ability to make melanin, which is why hair turns gray then eventually white.
Discover: How to Get Thicker Hair
Hair’s Growth Cycles
Now that you have a solid understanding of how hair is made, one final useful piece in the larger hair picture is in understanding the different cycles of hair growth the follicle goes through when producing hair.
At any given time, most of the follicles (about 90%) on your head will be in an active state of growth. This is called the anagen phase, and it can last anywhere from two to seven years, with hair on your head growing, on average, 6 inches per year.
Once the follicle starts to cycle down activity, it moves into the catagen phase, when the hair stops growing and detaches from the dermal papilla. This is a natural process that happens to all hair before it is shed. About 1% of your follicles are in this stage at any given time, and it can last anywhere from 10 days to four months.
The hair follicle then moves into the telogen phase when it’s ready to take a little break. Also known as the “resting phase,” about 10% of the follicles on your head are in this stage at any given time, and it can last upward of four months. During this phase, the follicle rests, and the hair just chills on your head before it is finally shed.
The exogen phase finally sees the hair come off the head. It’s completely normal to lose around 50 to 100 hairs per day, which probably sounds like a lot — but not if you recall that you have around 100,000 follicles on your head. The old hair shaft is pushed out as the new hair begins to grow, so the exogen and a new anagen phase overlap.
Check Out: The Ultimate Guide to Hair Growth Cycles
How To Grow Your Healthiest Hair Ever
Remember Dr. Ilyas’ comparison of the scalp to a bed of soil? Healthy soil is essential to growing healthy plants, just like a healthy scalp is essential to growing healthy hair. And a healthy scalp starts with a healthy body.
“In order to keep hair healthy, it must come out of a healthy scalp. This means that your body must be healthy,” explained Dr. Purvisha Patel of Advanced Dermatology & Skin Cancer Associates in Memphis, Tennessee.
In other words, a holistic approach to your overall health is essential to growing healthy hair. This means having lots of tools in your healthy living toolkit, including:
- Eating a well-balanced diet with plenty of protein, which provides the amino acids essential to hair growth.
- Making sure you’re getting hair-friendly vitamins and nutrients like vitamin B-7 (biotin), B-complex, zinc, iron and vitamins C, E and A.
- Choosing a revitalizing shampoo and give your scalp a light massage to promote circulation. Make sure to use the pads of your fingers (not your nails!) or a gentle scalp massager.
- Not pulling, twisting or overbrushing your hair.
- Managing stress as best you can because it really impacts hair growth.
- Applying a daily hair serum or foam to encourage thicker, fuller-looking hair.
“We need six glasses of water and eight hours of sleep every day. Take a multivitamin and a probiotic every day, too, to support hair growth. Being gentle with your scalp is important for the health of our hair shafts, so avoid irritating chemicals, excessive heat and physical trauma to the scalp,” added Dr. Patel.
Up Next: 6 Signs You Need a Scalp Detox (And How to Do It Right)
Hair: One of Your Body's Most Beautiful Assets
Now that you know the very complex process the human body goes through to produce hair strands, you should appreciate the end result even more and strive to protect and nourish it. You can promote your hair's wellness through a holistic approach that includes proper nutrition and targeted hair care that addresses your specific hair needs.
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