Basic Hair Anatomy Primer (or The Science-y Stuff … yawn)

Unless you’re a professional stylist or dermatologist, you probably don’t know much about hair. More to the point, you probably don’t know much about your hair and how to best take care of it in its natural state.

Most basic hair science is taught in cosmetology schools worldwide. So, I’ve dedicated this post to passing on common knowledge found in the Milady American Standard of Cosmetology and other science-y sources (best read while knocking back a shot  of expresso).

Knowledge is the foundation for good choices. That’s my philosophy. So, before you become a kitchen-bathroom chemist, let’s learn the fundamentals of hair so you understand what it needs.

Hair Anatomy 101

According to DermWeb, hair is roughly 65% to 95% keratin (a fibrous type of protein) plus lipids (fats) and trace environmental chemicals (from cosmetics, pollution, etc). The lipids – which increase during puberty and decrease with age — repel water.

Hair has two components – root and shaft. The root is where hair cells originate beneath the skin dermis. Once created, they grow, reproduce through cell mitosis and die. As new cells begin their life cycles, they divide then push dead cells through the skin surface in a tube-shaped casing called the follicle.

Hair Root

Each root is encased in the follicle below the skin’s surface.  At the very bottom of the root is a teeny-weeny canal called the dermal papilla which carries nutrients from the bloodstream to the hair bulb to nourish hair cells. Each root bulb is protected by three layers — the inner, fibrous and outer sheaths.

Hair Shaft

The hair shaft is the hair we see above the skin surface. It’s dead keratinized cells formed first in the inner root sheath and solidified in the hair follicle. It has three layers:

1.  Medulla. In simple terms, the medulla is the center layer of the shaft. It’s made of large, compressed cells. Fine hairs — like curly, kinky and coily hairs — typically don’t have a medulla.

2.  Cortex. As its name suggests, the cortex is the core of the hair that houses its pigment and keratin. It’s the life, shape, color and strength of the hair shaft. Curly and straight hair structures are distinctly different.

According to Schwartzkopt Professionals: Ask Education for Hairdressors, curly hair has two layers of cortex — the orthocortex and the paracortex.

The orthocortex lives on the outside of the curl. The paracortex lies inside the curl. It’s made of more compressed cells and is denser than the outer layer.

3.  Cuticle. Think of a shield. The cuticle is the hair shaft’s outermost protective layer. It’s a system of scales – like roof shingles or fish scales.

Microscopic image courtesy of M2Hair Blog,

Microscopic image courtesy of M2Hair Blog,

When the cuticle is compromised, the hair’s health is compromised.  Normally closed cuticles can protect the hair’s cortex and the hair’s integrity.

A raised cuticle weakens the hair shaft.



The hair follicle is a cylinder-shaped tube that plants the hair shaft into the skin. The follicle’s base — the root  bulb — is where hair cells grow and divide. Nearby blood vessels feed growing cells. As new cells emerge, the old, divided cells harden into hair through a process called keratinization. Then, they sprout like seedlings from the epidermis through the dermis.

Hair Growth Cycle

On average, hair grows a half-inch a month, according to WebMD. The normal hair life cycle has three phases:

Growth (Anagen) Phase. This is when the root bulb at the base of the follicle generates cells at a regular rate. Most visible hair is in this phase. The dying and hardening cells continually build the hair strand until the second phase.

Transitional (Catagen) Phase. Hair cell generation slows. Hair growth down-shifts and the gradually reduces in size.

Resting (Telogen) Phase. The hair stops growing and the follicle detaches resulting in normal hair shed. A new hair has begun forming within the follicle in its place. Hair normally sheds up to 100 hairs a day.

Dreadlocks form from the intentional  and controlled matting and interweaving of growing hair and accumulated shed hair.

Shape and curl pattern

Conventional hair wisdom asserts your hair type or texture is determined by what goes on in your follicle.

As explained by Schwarzkopf Professionals: Ask Education for Hairdressers, cell mitosis follows a circular pattern. If the cell division circulates in a uniform, even pattern and rate, it forms a hair shaft with a round diameter — similar to a cylinder — and the hair grows straight. If the cell mitosis circular pattern and rate is uneven — like an ellipse — then the hair formation kinks. Hair grows wavy,  curly, coily or kinky.

If you cut and magnify cross-sections of individual straight, wavy and curly hairs, you would see three distinct shapes: round, oval, elliptical and flat.

My cosmetology instructor explained it this way: think of a thin ribbon. When you run the blade of a scissor over its surface it curls into ringlets. It wouldn’t curl if the ribbon wasn’t flat.

Size and Density

American Standard Cosmetology has traditionally classified hair according to density. Hair texture is generally fine, medium (or normal) or coarse depending on the size of the follicle and the condition of the cuticle.

  • Fine Hair has a small circumference
  • Coarse Hair  has a large circumference
  • Medium (Normal) Hair falls between the range of fine and coarse hair.

Hello? Do I hear the faint sound of crickets? I admit this stuff can be boring, but don’t overlook it. Basic hair knowledge will keep you from a world of hurt. Many of us have suffered scalp burns from chemicals,  lost hair from years of wearing hair extensions and just plain ignorance. What you didn’t know about hair did hurt you.



“Skin Problems and Treatments: Picture of the Hair, Hair (Human Anatomy),” WebMD,


“Chapter 4: The Skin, Hair and Nails,” O’Rahilly, Muller, Carpenter and Swenson, Dartmouth University,

Hair Biology Index,,

 Schwarzkoft Professionals: Ask Education for Hairdressers,

Hair Loss Symptoms Overview, WebMD,

Davidson College, Biology,

Hair Growth Assessment Techniques, Ulrike Blume-Peytavi, Kathrin Hillmann, Marcella Guarrera

Hair Evaluation Methods,

Hair Dressing Training, UK,

Black Hair Science,