What Is the Study of Hair Called?

The scientific study of hair and its disorders is called trichology, a term derived from the Greek word “thrix” meaning hair. The field traces back to 1860, when what began as a quasi-scientific interest in hair loss and hair care in a London barbershop eventually grew into a recognized discipline, complete with the founding of the Institute of Trichologists.¹ But trichology today extends well beyond hair loss remedies. It overlaps with dermatology, immunology, forensic science, and even microbiology, making it far broader than most people expect.

How Trichology Became a Discipline

Trichology’s roots are unusual for a medical field. Most scientific specialties emerged from universities or hospitals. Trichology started among barbers. In Victorian-era London, concerns about baldness and scalp ailments drove the first organized effort to study hair in a structured way. The founding of the Institute of Trichologists in 1860 gave the field an institutional home, but it took decades for trichology to earn credibility alongside mainstream medicine.¹ Today, debate continues over whether hair-related medical practice falls under the umbrella of trichology, dermatotrichology, or should be rebranded entirely. The practical reality is that dermatologists handle the clinical side, while trichologists in many countries fill a complementary role that focuses more on non-surgical hair and scalp care.

What the Hair Follicle Actually Does

To study hair, you have to study the follicle, and the follicle is a surprisingly complex organ. Hair is produced from follicles that are controlled by a cluster of specialized cells at the base called the dermal papilla. These cells first signal hair follicle formation during embryonic development by interacting with the overlying skin cells, and they continue to regulate growth, thickness, color, and hair type throughout life.² Think of the dermal papilla as a tiny command center: it secretes a range of chemical signals that tell the follicle when to grow, when to rest, and what kind of hair to produce.

The hair fiber itself is remarkably strong for its size, with a tensile strength roughly comparable to steel wire of the same diameter. Under tension, the internal protein structure of hair can actually unwind and reorganize, which is what gives it that surprising stretchiness before it snaps.³ That strength comes from keratin, a tightly packed protein rich in sulfur-containing bonds that hold the fiber together. These bonds are also the weak point that chemical treatments exploit, as we’ll see later.

The Hair Growth Cycle

Hair does not grow continuously. Each follicle cycles through four phases: anagen (active growth), catagen (a brief transition), telogen (rest), and exogen (shedding). Anagen is when the follicle is rapidly producing a hair shaft, a phase that can last several years on the scalp. Catagen is a short wind-down period, and telogen is the resting state, where the follicle sits idle while still holding onto the old hair. At any given moment, roughly 9% of your scalp follicles are in telogen.⁴

What pushes follicles from growth into rest? Inflammation, hormonal shifts, stress, poor sleep, nutritional gaps, and certain medications can all trigger an early shift from anagen to telogen. On the flip side, increased blood flow to the scalp, direct stimulation of follicles, and growth factors encourage resting follicles to start growing again.⁴ This is why stress-related hair shedding, known as telogen effluvium, tends to appear a few months after a stressful event: the follicles were pushed into telogen prematurely, and the hair falls out only when they eventually cycle through to exogen.

Telogen itself is more dynamic than it sounds. Rather than simply sitting dormant, resting follicles can be divided into an early “refractory” phase, where they resist signals to regrow, and a later “competent” phase, where they are primed and ready to launch a new cycle. Telogen follicles also respond to circadian rhythms, essentially timing their re-entry into growth based on the body’s internal clock.⁵ The upshot is that “resting” hair is not truly dormant; it is actively preparing for its next round of growth.

Why Hair Goes Gray

Graying is one of the most visible signs of aging, and the mechanism is more interesting than simple wear and tear. For years, the dominant theory was that melanocytes, the pigment-producing cells in the follicle, gradually self-destructed because making melanin is chemically harsh. That turns out to be incomplete. Research using both mouse models and aging human hair follicles demonstrated that graying is primarily caused by the failure of melanocyte stem cells to maintain themselves in their niche at the base of the follicle.⁶ Instead of staying put and renewing themselves properly, these stem cells drift out of position and differentiate prematurely, producing pigment in the wrong place at the wrong time. Over successive hair cycles, the pool of melanocyte stem cells shrinks until there are none left to supply color.⁷

Oxidative damage still plays a role, just not the starring one. It appears to disrupt melanocyte survival and the chemical machinery of pigment production, accelerating the process. Once the melanocyte stem cell reservoir in the bulge region of the follicle is depleted, graying becomes largely irreversible.⁸ This is why no supplement or topical product has been shown to reliably reverse established gray hair. The cells needed to make pigment are simply gone.

The Follicle’s Hidden Immune Shield

One of trichology’s more surprising discoveries is that hair follicles maintain a form of immune privilege. During the active growth phase, the lower portion of the follicle, from the bulge down to the bulb, actively suppresses the body’s immune surveillance. The follicle uses both passive barriers and active signaling to keep immune cells from attacking structures it needs to grow hair.⁹ This is similar to the immune privilege seen in the eyes and testes, where overzealous immune responses would cause serious damage.

When this immune privilege collapses, the consequences are dramatic. Alopecia areata, the autoimmune condition that causes patchy or total hair loss, results from a breakdown of this immune shield. Inflammatory T cells swarm the hair bulb, attacking the follicle and forcing it into premature regression.¹⁰ Excitingly, researchers have recently shown that a specialized subset of regulatory immune cells can be used to restore follicular immune privilege and even promote hair regrowth in human models of alopecia areata, opening a potential avenue for cell-based therapies.¹¹

How Hair Problems Get Diagnosed

Trichoscopy is the main non-invasive tool used to evaluate hair and scalp disorders. It works by using a magnifying lens (the same type of device used in dermoscopy) to examine the scalp at magnifications up to 160 times normal vision.¹² Under trichoscopy, a trained eye can distinguish between different hair types, count the number of hairs emerging from each follicular opening, and identify abnormal patterns like empty follicles, tiny “exclamation mark” hairs typical of alopecia areata, or yellow and black dots that indicate specific kinds of follicle damage.

The practical value is that trichoscopy can often reach a diagnosis without a biopsy. For many common hair loss conditions, the scalp patterns visible under magnification are distinctive enough to tell them apart. When a biopsy is still warranted, trichoscopy helps identify exactly where to sample for the most useful result.¹³

The Scalp Microbiome

The scalp hosts a complex community of fungi and bacteria that plays a bigger role in hair health than most people realize. In healthy scalps, the main fungal residents belong to the genus Malassezia, and the dominant bacteria include Cutibacterium and Staphylococcus species. In people with seborrheic dermatitis or persistent dandruff, researchers consistently find a shift in the balance: the ratio of different Malassezia species changes, and Staphylococcus starts to dominate over Cutibacterium.¹⁴ This shift matters because Staphylococcus overgrowth is linked to damage in the skin barrier of the scalp, including higher water loss and altered pH, while Cutibacterium appears to help retain moisture.

Malassezia species have also been flagged as potential biomarkers for seborrheic dermatitis, along with Staphylococcus and other bacteria, meaning their presence in unusual proportions could eventually help diagnose scalp conditions before they become severe.¹⁵ This line of research is still young, but it suggests that managing your scalp’s microbial balance could matter as much for hair health as anything you do to the hair fiber itself.

What Chemical Treatments Do to Hair

Trichology has a lot to say about what happens when you bleach, dye, or chemically straighten your hair. At the molecular level, bleaching attacks melanin granules and oxidizes the sulfur-containing bonds that hold keratin proteins together, converting the strong disulfide bridges into a weaker form called cysteic acid. Even mild bleach treatments cause extensive melanin degradation, and the primary damage concentrates in the cortex, the structural core of the hair fiber.¹⁶

Chemical straightening products cause their own problems. Formaldehyde-based straighteners increase cuticle irregularity, and glyoxylic acid formulations cause even more damage to the hair surface, despite sometimes leaving hair looking shinier in the short term.¹⁷ The combination of chemical processing and UV exposure is particularly rough on hair. Bleaching and dyeing paired with sunlight exposure significantly increase the force needed to comb through hair, especially in tightly curled fibers, which also show measurable protein loss and cuticle erosion under scanning electron microscopy.¹⁸

Genetics of Hair Shape and Texture

Why some people have pin-straight hair while others have tight coils is a genetic question that trichology intersects with. Hair curliness varies tremendously across populations and geography, and researchers are zeroing in on the genes responsible. A genome-wide study comparing individuals with low and high curl identified strong links to variation in trichohyalin (a protein involved in forming the inner root sheath of the follicle), a copper transporter protein called CUTC, and keratin 74, another inner root sheath component.¹⁹ The shape of the follicle itself, and specifically how symmetrically the inner root sheath wraps around the growing fiber, appears to determine whether the hair emerges straight or curves. The genetics set the follicle geometry, and the geometry sets the curl.

Hair as a Forensic Record

Outside the clinic, hair has become an important tool in forensic science. Because hair grows slowly and incorporates substances from the bloodstream as it forms, a single strand can serve as a timeline of drug exposure. Forensic toxicologists use hair testing to assess both single-dose events and long-term exposure patterns, which makes it valuable in drug-facilitated crime investigations and cause-of-death determinations.²⁰ While blood and urine offer a snapshot of recent hours or days, hair can record months of chemical history, depending on its length. This window of detection has made hair analysis increasingly common in workplace drug testing and legal proceedings.

Trichotillomania and the Psychodermatology Connection

Trichology also borders on psychiatry through conditions like trichotillomania, the compulsive pulling of one’s own hair. This is classified as a psychiatric condition, and in people who seek treatment, it can be severe, chronic, and difficult to manage.²¹ The impact goes beyond the scalp. Research comparing people with trichotillomania to matched controls found that hair pulling causes wide-ranging impairments across daily functioning, including negative self-evaluations, disrupted social interactions, and reduced work productivity. The severity of pulling itself predicted some of these impairments independently of depression.²² Trichologists and dermatologists are often the first professionals to see the physical evidence of trichotillomania, even before a patient has been referred for psychological help, so awareness of the condition sits squarely within their scope.

Emerging Therapies in Hair Regeneration

The frontier of trichology is regenerative. Researchers are exploring ways to coax dormant follicles back to life or even grow entirely new ones. Therapies gaining attention include low-level laser therapy, microneedling, fractional radiofrequency, platelet-rich plasma injections, and stem cell therapy.²³ Each approach targets the follicle from a different angle. Low-level lasers and microneedling aim to stimulate blood flow and growth factor release. Platelet-rich plasma delivers a concentrated dose of the patient’s own growth factors directly to the scalp. Stem cell therapy is the most ambitious, aiming to replace or rejuvenate the dermal papilla cells that drive hair formation in the first place. None of these has fully replaced established treatments like minoxidil or hair transplantation, but the pace of research suggests the field is on the verge of real breakthroughs in the next decade.