Reference
Glossary
The vocabulary of hair biology and care, defined in plain language. Terms used throughout the site link here so you can check a definition without losing your place.
A
- Alopecia areata
- An autoimmune hair-loss condition that can produce smooth patches or more extensive loss.
- Anagengrowth phase, anagen phase
- The active phase in which a follicle produces a growing hair fiber. Read more
- Androgenetic alopeciamale pattern hair loss, male pattern baldness, AGA
- A common pattern of progressive follicle miniaturization influenced by genetic and androgen-related factors. Read more
B
- Basic or ingredient-focused hair supplement
- A simple supplement centered on one featured nutrient, protein ingredient, or a small vitamin blend.
- Bioactive
- A substance selected because it can interact with a biological pathway or outcome.
- Blinding
- Keeping participants, investigators, or outcome assessors unaware of assigned intervention when practical.
C
- Catagentransition phase
- A brief transition phase in which active hair production slows and the lower follicle regresses. Read more
- Clinically studied active
- An exact active ingredient evaluated in people for a defined dose, population, duration, and outcome.
- Comprehensive hair supplement
- A multi-active oral formula designed to combine several defined nutritional or biological support roles.
- Cortex
- The main structural region of the hair shaft that contributes to strength, shape, and pigment appearance.
- Cosmetic hair care
- Cleansing, conditioning, styling, and repair products used mainly for scalp-surface or emerged-shaft outcomes.
- Cuticle
- The outer protective layer of overlapping cells on a hair fiber.
D
- Delivery route
- The path by which an intervention enters or acts on the body, such as oral, topical, device-based, injected, or surgical.
- Dermal papilla
- A specialized connective-tissue structure at the base of an active follicle that participates in growth signaling.
- Dietary supplement
- A product regulated as a dietary supplement rather than as a drug for disease treatment.
- Dihydrotestosterone (DHT)dihydrotestosterone, DHT
- An androgen formed from testosterone by the enzyme 5-alpha-reductase. Read more
- Disease claim
- A claim that a product diagnoses, treats, mitigates, cures, or prevents a disease.
- Dose matching
- Comparing the amount used in a product with the daily amount evaluated in a relevant study.
E
- Endpoint
- A defined outcome measured in a study, such as hair count, density, shedding, caliber, or quality of life.
- Evidence object
- The exact intervention, product, dose, route, population, and outcome to which an evidence grade applies.
- Exogen
- The portion of the cycle in which an old hair fiber is released from the follicle.
F
- FDA approved
- A status indicating that FDA approved a specific drug or product for a defined labeled use.
- FDA cleared
- A device status commonly based on a defined regulatory pathway and intended use.
- Finasteride
- A prescription 5-alpha-reductase inhibitor with an approved 1 mg use for male pattern hair loss in men.
- Finished-product evidencefinished product trial
- Research that evaluates the complete product in the form and serving used by consumers. Read more
- Follicular unit extraction (FUE)
- A hair-transplant harvesting method that removes follicular units individually from the donor area.
H
- Hair breakage
- Fracture of the emerged hair shaft rather than release of the whole fiber from the follicle.
- Hair caliber
- The diameter or thickness of an individual hair fiber.
- Hair density
- The number of visible or measured hair fibers within a defined scalp area.
- Hair follicle
- The living skin mini-organ that repeatedly produces a hair fiber.
- Hair growth cycle
- The recurring sequence of active growth, transition, rest, and fiber release followed by each follicle.
- Hair shaft
- The nonliving fiber that emerges above the skin surface.
- Hair-loss red flags
- Features that make professional assessment more important than routine self-care alone.
- Heterogeneity
- Meaningful variation among studies in populations, interventions, methods, or results.
I
- Ingredient-level evidence
- Research that evaluates a specific ingredient or preparation rather than the complete commercial formula.
L
- Low-level light therapy (LLLT)
- Repeated exposure of the scalp to defined red or near-infrared light parameters using a device.
M
- Mechanistic evidence
- Evidence that an intervention affects a biological pathway, often in cells, tissue, animals, or laboratory measures.
- Medicated shampoo
- A shampoo containing an active intended for a defined scalp condition or drug use.
- Melanin
- Pigment produced by melanocytes and incorporated into a hair fiber while it forms.
- Microneedling
- Controlled skin needling performed with a defined device, depth, schedule, and aftercare plan.
- Miniaturization
- Progressive production of finer and often shorter fibers by susceptible follicles.
O
- Off-label use
- Use of an approved drug for a dose, route, population, or indication outside its approved labeling.
- Over the counter (OTC)
- Available without an individual prescription when sold and used within its applicable category and labeling.
- Oxidative stressfree radical damage
- An imbalance between reactive molecules and the systems that control or repair their effects. Read more
P
- Pattern hair loss
- Progressive thinning that follows a characteristic distribution and is commonly related to androgenetic alopecia.
- Placebo
- An inactive or comparison intervention designed to resemble the treatment being studied.
- Platelet-rich plasma (PRP)
- An autologous blood-derived preparation injected into the scalp using a clinician-selected protocol.
R
- Randomized controlled trial (RCT)
- A study that assigns participants to interventions by chance and compares outcomes between groups.
- Regulatory status
- The legal and regulatory category governing a drug, device, supplement, cosmetic, or procedure for a specific use.
S
- Scarring alopecia
- A group of conditions in which inflammation can damage follicles and replace them with scar tissue.
- Shedding
- Release of a hair fiber from a follicle, commonly during exogen.
- Standardized extract
- An ingredient produced to contain a defined amount or range of selected marker compounds.
- Standardized photography
- Repeat photography using consistent camera, distance, angles, lighting, hair condition, and styling.
- Stratum corneum
- The outermost layer of the epidermis and an important barrier to topical delivery.
- Structure/function claimstructure function claim
- A dietary-supplement claim about supporting normal body structure or function rather than diagnosing or treating disease. Read more
- Surrogate endpoint
- A laboratory or intermediate measure used in place of a direct clinical or consumer outcome.
- Systematic review
- A structured review that searches for, selects, evaluates, and synthesizes studies using predefined methods.
- Systemic exposure
- The amount of an active ingredient or drug present in the bloodstream and available to tissues beyond the application site.
T
- Telogenresting phase, telogen phase
- A relative resting phase of the follicle before or during release of the old fiber. Read more
- Telogen effluviumstress shedding, diffuse shedding
- Diffuse shedding associated with an increased number of follicles moving toward rest and release.
- Terminal hair
- A relatively thick, pigmented hair fiber compared with fine vellus-like hair.
- Topical vehicle
- The liquid, foam, gel, cream, or other formulation that carries an active ingredient onto or through the skin.
V
- Vellus hair
- A fine, short, lightly pigmented or nonpigmented hair fiber.