How Your Hair Actually Works (And Why It Matters for How You Care for It)

Most hair blogs start with the same line: "Your hair is your crowning glory." Then they tell you what a follicle is, label some diagrams, and list the three phases of the growth cycle.

You leave knowing more words. You don't leave making better decisions.

This blog is different. We're going to walk through your hair's architecture, from follicle to tip, and at every stop, connect the biology to something practical: why your hair changed, why certain products work and others don't, why the strand on your head can't be "healed," and what "hair health" actually means when you strip away the marketing.

If you've been reading our skin blogs, you already know the approach. Understand the architecture. Then every decision gets simpler.

Your Hair Has Two Parts (And Only One Is Alive)

This is the most important distinction in all of hair biology, and it's the one the industry works hardest to blur.

The root lives inside your skin, anchored in a structure called the follicle. The root is alive. It receives blood supply, nutrients, and oxygen through a tiny structure at its base called the papilla. New cells form here, harden into keratin, and get pushed upward as more cells form beneath them. This is where hair is made.

The shaft is everything above the skin surface. It's the hair you see, touch, and style. And it's dead.

Not metaphorically dead. Biologically dead. The cells that make up the shaft hardened and lost their nuclei before they ever left the follicle. They cannot repair themselves. They cannot absorb nutrients from your bloodstream. They cannot be "nourished" by what you eat or drink. They cannot be hydrated from within.

Every strand of hair on your head is a finished product. The factory (the follicle) made it, and once it left the factory, it was done.

This is why we keep saying: you're not feeding your hair, you're feeding the factory that makes it. And you're protecting the finished product from the outside, because the finished product can't protect itself.

The Three Layers of a Hair Strand (And the Only One That Matters for Your Routine)

Each strand has three concentric layers, like rings in a tree trunk:

The medulla. The innermost core. It's present in thick, coarse hair and often absent in fine hair. For practical purposes, the medulla has no relevance to your haircare routine. It exists. You can't interact with it. Moving on.

The cortex. The thick middle layer. This is where the structural proteins (keratin) live, where the bonds that determine your hair's strength and elasticity are formed, and where melanin (pigment) is deposited. The cortex is what gives your hair its color, its texture, and its tensile strength. When hair is "damaged at the structural level" (from chemical processing, extreme heat, or severe mechanical stress), it's the cortex that's been compromised.

You can't directly access the cortex with a topical product under normal circumstances. It's protected by the outermost layer. Which brings us to the one that matters most:

The cuticle. The outermost layer. Overlapping cells arranged like shingles on a roof. This is the layer that determines how your hair looks, feels, and performs on a daily basis.

When the cuticle cells lie flat: the strand is smooth, shiny (light reflects evenly off the flat surface), flexible, resistant to moisture loss, and protected from environmental damage.

When the cuticle cells are lifted, roughened, or stripped away: the strand is dull (light scatters off the uneven surface), rough to the touch, prone to tangling, loses internal moisture rapidly, and is vulnerable to breakage.

Every haircare product you use interacts primarily with this layer. Shampoo can lift cuticle cells (especially harsh surfactants). Conditioner smooths them back down. Heat tools blast them open. Cold water helps seal them. Styling products coat them. Chemical treatments (color, perms, relaxers) penetrate through them to alter the cortex beneath.

The cuticle-first framework we use for haircare decisions is built on this anatomy: every step either preserves the shingles or damages them.

Why Straight Hair Shines and Curly Hair Looks Dryer

This is one of the most common questions we get, and the answer is structural.

The cross-sectional shape of your hair determines its curl pattern. Round cross-sections grow straight. Oval cross-sections curl. The more oval, the tighter the curl.

Shine is determined by how evenly light reflects off the strand's surface. Straight hair has a uniform surface that reflects light like a mirror. Curly hair has bends, twists, and varying angles that scatter light in multiple directions. Same cuticle condition, different optical result.

But there's a second factor: sebum distribution. Your scalp produces sebum (oil) that naturally coats and lubricates the hair shaft. On straight hair, sebum travels easily from root to tip, providing a natural conditioning layer along the entire length. On curly hair, the bends and coils prevent sebum from migrating down the shaft. The roots may be adequately oiled while the ends are completely dry.

This is why curly hair tends to need more external conditioning and less frequent washing than straight hair. It's not more "damaged." It's architecturally less able to self-lubricate.

The Growth Cycle (And Why It Matters After 50)

Your hair doesn't grow continuously. Each follicle cycles independently through three phases:

Anagen (growth). The active phase. New cells form in the bulb, harden, and push the strand upward at roughly 1cm per month. On your head, this phase can last 2 to 7 years, which is why head hair can grow so long. For eyebrows and eyelashes, anagen lasts only 100 to 150 days, which is why they stay short. At any given time, about 90% of your head hair is in anagen.

Catagen (transition). Growth slows and the root separates from its blood supply. This phase lasts 2 to 3 weeks. About 3% of your hair is in catagen at any time.

Telogen (rest and release). The strand sits in the follicle, detached from the papilla, for several months. Eventually it falls out (this is normal daily shedding, typically 50 to 100 hairs per day). The follicle then begins producing a new hair, and the cycle restarts.

Why this matters after 50: The anagen phase shortens with age and hormonal changes. Follicles spend less time actively growing and more time resting. The strands produced during shorter anagen phases are thinner and may not reach the same length before entering catagen. This is why hair gradually becomes finer and less dense after menopause, even without pathological hair loss.

Estrogen decline affects the follicle the same way it affects the skin: reduced nutrient delivery, less collagen support for the follicle structure, and a shifted hormonal balance that can shorten anagen and increase telogen shedding.

The nutritional support your hair needs (iron, zinc, protein, vitamin D, omega-3s) matters specifically during anagen. That's the only phase where the follicle is actively producing. What you eat today affects the quality of the strand being built right now, not the strand that left the follicle months ago.

Hair Color, Graying, and What's Actually Happening

Hair color comes from melanin deposited in the cortex during production. Two types of melanin (eumelanin for brown/black, pheomelanin for red/blonde) combine in varying ratios to produce your specific shade.

Graying happens when melanocyte stem cells in the follicle decline. Fewer melanocytes means less melanin deposited in each new strand. The strand isn't "turning gray." It's growing in with less pigment. Eventually, with no melanin production at all, the strand grows in white.

This process is primarily genetic. It's not caused by stress (though severe physiological stress can trigger temporary graying in some cases). It's not reversed by any supplement, food, or topical product. It's a gradual depletion of the pigment-producing cells in each follicle.

What "Hair Health" Actually Means

The industry uses "hair health" to sell products, but the term is misleading because the visible part of your hair isn't alive.

Here's what it actually means when you separate the marketing from the biology:

Follicle health is about the living root and its environment. A well-nourished follicle with adequate blood supply, balanced hormones, and a healthy scalp produces stronger, thicker strands during a longer growth phase. This is influenced by nutrition, hormones, scalp care, and overall health.

Strand condition is about the dead shaft and its cuticle. A well-maintained cuticle retains moisture, resists breakage, reflects light evenly, and feels smooth. This is influenced by how you wash, condition, dry, and style the hair that's already there.

Two completely separate systems. One alive, one dead. One fed from within, one protected from without. Both matter. Neither replaces the other.

Understanding this distinction is the single most useful thing you can learn about your hair. It tells you where nutrition, supplements, and internal health matter (the follicle). It tells you where products, conditioners, and gentle handling matter (the strand). And it stops you from expecting either system to do the other's job.

Frequently Asked Questions

Is hair dead or alive? The shaft (everything above the scalp) is dead. The root (inside the follicle, beneath the skin) is alive. This is why topical products can protect the strand but can't "heal" it, and why nutrition matters for new growth but can't change existing hair.

Why does hair get thinner with age? The growth phase (anagen) shortens with age and hormonal changes, particularly after menopause. Follicles produce thinner strands during shorter growth periods, and more follicles spend time in the resting phase. Estrogen decline reduces nutrient delivery and structural support to the follicle.

What determines hair texture (straight vs. curly)? The cross-sectional shape of the hair strand. Round cross-sections produce straight hair. Oval cross-sections produce wavy or curly hair. The more oval the shape, the tighter the curl. This is genetically determined.

Why does curly hair look drier than straight hair? Two reasons: sebum (natural oil) can't travel down the bends and coils to lubricate the full length, and the curved surface scatters light rather than reflecting it evenly. Curly hair isn't inherently drier at the cuticle level, but it appears drier and needs more external conditioning.

What causes gray hair? Melanocyte stem cells in the hair follicle gradually decline with age, producing less melanin in each new strand. The hair isn't "turning" gray. New strands are growing in with reduced pigment. The process is primarily genetic and is not reversible through diet, supplements, or topical products.

How fast does hair grow? Approximately 1cm (about half an inch) per month on the scalp. Eyebrows, eyelashes, and body hair grow more slowly, with shorter growth phases that limit their maximum length.

Sources

Hoover, E., et al. "Physiology, Hair." StatPearls. National Library of Medicine. 2023. https://www.ncbi.nlm.nih.gov/books/NBK499948/

Buffoli, B., et al. "The human hair: from anatomy to physiology." International Journal of Dermatology. 2014. https://pubmed.ncbi.nlm.nih.gov/24372228/

Schneider, M.R., et al. "Advances in Understanding Hair Growth." American Journal of Clinical Dermatology. 2009. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4755418/

Thornton, M.J. "Estrogens and aging skin." Dermato-Endocrinology. 2013. https://pmc.ncbi.nlm.nih.gov/articles/PMC3772914/