Hair Loss Glossary

An enzyme that converts testosterone into dihydrotestosterone (DHT). There are two types: Type I (found in the skin and liver) and Type II (concentrated in the scalp and prostate). Blocking this enzyme is the primary mechanism of finasteride and dutasteride.

The general medical term for hair loss. It encompasses many distinct conditions, from genetic pattern baldness to autoimmune and stress-related forms. Not a single diagnosis — always qualified by type (e.g., alopecia areata, androgenetic alopecia).

An autoimmune condition in which the immune system mistakenly attacks hair follicles, causing patchy, unpredictable hair loss on the scalp or body. It can progress to alopecia totalis (full scalp) or alopecia universalis (full body). Treatment targets immune modulation.

A complete loss of all hair on the scalp. Considered a more advanced form of alopecia areata. Distinct from androgenetic alopecia.

Complete loss of hair across the entire body, including eyebrows, eyelashes, and body hair. The most severe form of alopecia areata.

The active growth phase of the hair cycle, during which the hair shaft is actively produced. Scalp hairs typically remain in anagen for 2–7 years. The proportion of hairs in anagen at any one time (anagen rate) is a key measure of scalp health — treatments like minoxidil and melatonin work partly by extending this phase.

The most common form of hair loss, affecting up to 95% of men and a significant proportion of women. Caused by genetic sensitivity of hair follicles to dihydrotestosterone (DHT), leading to progressive follicle miniaturization. Presents as a receding hairline and crown thinning in men, and diffuse thinning along the part line in women.

A B-vitamin (B7) often marketed for hair and nail health. Biotin deficiency can cause hair loss, but true deficiency is uncommon. Supplementation is unlikely to benefit those who are not deficient. Despite widespread use, clinical evidence for biotin improving hair growth in non-deficient individuals is limited.

A well-supported topical ingredient for hair retention. Research shows it penetrates the follicle and counteracts DHT's suppressive effects on hair shaft elongation. It also stimulates keratinocyte proliferation, extending the anagen phase. Topical application avoids the systemic effects of ingested caffeine.

A patented ingredient combining a biomimetic peptide (acetyl tetrapeptide-3) and red clover extract. It strengthens the anchoring of hair in the follicle and reduces scalp inflammation — two independent pathways linked to hair shedding. Often combined with Redensyl™ and Procapil™ in premium OTC formulations.

A short transitional phase of the hair cycle lasting approximately 2–3 weeks, during which the hair follicle regresses and detaches from its blood supply. Roughly 3% of hairs are in catagen at any given time.

A group of rare conditions in which inflammation permanently destroys hair follicles and replaces them with scar tissue. Unlike non-scarring forms of hair loss, follicle damage is irreversible. Early diagnosis and treatment are critical to halt progression.

A medication prepared by a licensed compounding pharmacy, custom-made for an individual patient. In hair loss, this often means combining ingredients like finasteride, minoxidil, and tretinoin into a single topical formulation at tailored concentrations — not possible with commercially manufactured products.

Hair loss at the top (vertex) of the scalp, typically associated with male and female pattern hair loss. Often one of the first visible signs of androgenetic alopecia in men, alongside a receding hairline.

A cluster of specialized cells at the base of each hair follicle that regulate hair growth signaling. The dermal papilla communicates with stem cells in the follicle to control the hair growth cycle. It is a key target for many regenerative hair loss therapies.

A potent androgen derived from testosterone via the 5-alpha reductase enzyme. In genetically predisposed individuals, DHT binds to receptors in scalp follicles and progressively shrinks (miniaturizes) them, shortening the growth cycle until the follicle can no longer produce visible hair. Reducing DHT is the core mechanism of finasteride and dutasteride.

A pattern of hair loss distributed evenly across the scalp rather than in a defined zone. More common in women than men. Causes include female pattern hair loss, telogen effluvium, iron deficiency, and thyroid disorders.

A prescription 5-alpha reductase inhibitor that blocks both Type I and Type II enzymes, achieving greater DHT suppression (~90–95%) than finasteride (~70%). Used off-label for androgenetic alopecia and often considered for cases where finasteride has produced insufficient results. Available in oral and topical forms from specialist providers.

The female equivalent of androgenetic alopecia. Presents as diffuse thinning along the central part line and crown rather than a receding hairline. Hormonal sensitivity to androgens is a key driver, though the mechanism differs from the male variant. Classified using the Ludwig scale.

The primary protein used by the body to store iron. Low ferritin — even before full iron-deficiency anemia develops — can impair the hair growth cycle and is one of the most commonly overlooked causes of diffuse hair loss in women. A ferritin blood test is often the first step in evaluating hair loss in women.

The most widely prescribed oral medication for androgenetic alopecia. A Type II 5-alpha reductase inhibitor that reduces scalp DHT by approximately 70%. Requires a prescription and ongoing medical monitoring. Also available in topical form, which may reduce systemic exposure and associated side effects.

A topical corticosteroid sometimes added to hair loss formulations to reduce scalp inflammation. While it can be beneficial in inflammatory hair loss conditions, long-term use carries risks including skin thinning. Its inclusion in standard androgenetic alopecia treatments is considered by some clinicians to be unnecessary.

The progressive shrinking of hair follicles in response to DHT or aging. As follicles miniaturize, they produce thinner, shorter, and lighter hairs over successive growth cycles — eventually producing only vellus (fine, colorless) hairs, and ultimately no hair at all. This is the core pathological process in androgenetic alopecia.

A hair transplant technique in which individual follicular units are harvested one by one from the donor area (typically the back of the scalp) and transplanted to thinning areas. Leaves minimal scarring compared to FUT. Results are permanent for transplanted follicles, but does not stop ongoing hair loss in non-transplanted areas.

A hair transplant technique in which a strip of scalp is removed from the donor area and follicular units are dissected from it before transplantation. Allows a larger number of grafts in a single session but leaves a linear scar.

The recurring sequence of phases through which each hair follicle passes: anagen (growth), catagen (transition), and telogen (resting/shedding). The length and quality of each phase determines hair density and length. Disruptions to this cycle — by hormones, stress, or nutritional deficiencies — underlie most forms of hair loss.

A nutritional deficiency that can disrupt the hair growth cycle and contribute to diffuse hair shedding, particularly in women. Iron is essential for DNA synthesis in rapidly dividing hair follicle cells. Low ferritin can impact hair growth even without full-blown anemia.

The primary cell type in the outer layer of the skin and the hair shaft. In the follicle, keratinocytes proliferate to build the hair shaft. Ingredients like topical caffeine stimulate keratinocyte proliferation, extending the anagen phase and supporting hair density.

An antifungal agent used in shampoos that may also have mild anti-androgenic effects at the scalp level. Often used as a complementary approach alongside prescription treatments. Evidence suggests it can improve hair density, though it is not a primary standalone treatment.

A prostaglandin analog originally used to treat glaucoma that has shown some evidence of stimulating hair growth when applied topically. Its long-term safety data for scalp use is limited, and some clinicians caution against its routine inclusion in compounded hair loss formulations.

A non-invasive treatment that uses red or near-infrared light to stimulate follicle activity. Available as in-office devices or FDA-cleared home-use caps and combs. Some clinical studies support modest benefit in androgenetic alopecia. Generally used as a complementary therapy rather than a primary treatment.

The standard classification system for female pattern hair loss, divided into three grades based on the degree of diffuse thinning along the central part. Analogous to the Norwood Scale for men.

Best known as a sleep hormone, melatonin is also a potent antioxidant. Hair follicles contain melatonin receptors, and topical application has been shown in randomized controlled trials to increase anagen hair rate and reduce telogen shedding. It protects follicles from oxidative stress — a key driver of follicle dysfunction and premature aging.

One of the most widely used and well-studied hair loss treatments. Originally a blood pressure medication, it was found to stimulate hair growth as a side effect. It works by prolonging the anagen phase and improving blood flow to follicles. Available over the counter in topical 2% and 5% formulations, and by prescription in oral form (low-dose). Effective for both men and women.

The standard classification system for male pattern hair loss, ranging from Type I (no significant loss) to Type VII (only a band of hair remaining at the sides and back of the scalp). Used by clinicians to assess severity and guide treatment decisions.

An imbalance between the production of reactive oxygen species (free radicals) and the body's ability to neutralize them with antioxidants. Oxidative stress is a documented driver of hair follicle damage and premature aging of the follicle. Antioxidant ingredients like topical melatonin and vitamin E help counter this.

A procedure in which a patient's own blood is drawn, spun in a centrifuge to concentrate the platelets, and injected into the scalp. Platelets release growth factors that may stimulate follicle activity. Evidence is promising but not yet conclusive. Typically requires repeat sessions and is usually used alongside other treatments.

Diffuse hair shedding that occurs in the months following childbirth, typically peaking around 3–4 months postpartum. Caused by a drop in estrogen levels triggering large numbers of follicles to shift from anagen to telogen simultaneously. Affects up to 50% of new mothers and is typically self-resolving within 6–12 months.

A patented ingredient combining vitamin B5, biotinyl-GHK (a peptide), and oleanolic acid. It improves blood circulation to the follicle and directly counters DHT-driven miniaturization. Frequently paired with Redensyl™ and Capixyl™ in OTC hair loss serums.

A common solvent used in topical formulations to enhance ingredient penetration. While generally regarded as safe, it can cause scalp irritation in sensitive individuals — including redness, itching, and flaking. Some premium compounding pharmacies formulate without it at the request of patients or prescribers.

The retreat of the hairline from the forehead, typically beginning at the temples. One of the earliest visible signs of androgenetic alopecia in men. The degree and pattern of recession is captured by the Norwood classification system.

A patented ingredient that targets stem cells in the hair follicle bulge, reactivating dormant follicles and pushing them from telogen back into anagen. Clinical studies report a significant reduction in hair loss and improvement in hair density. Frequently combined with Capixyl™ and Procapil™.

A natural DHT inhibitor derived from the berries of Serenoa repens. Works by blocking the 5-alpha reductase enzyme — the same pathway targeted by finasteride and dutasteride — reducing DHT at the follicle level. Clinical studies show it can reduce hair loss and improve hair density with a favorable side effect profile. Available in oral and topical forms.

A cosmetic tattooing technique in which pigment is deposited into the scalp to create the appearance of a closely cropped or shaved head. Does not regrow hair but can effectively camouflage thinning or baldness. Results are long-lasting but require touch-ups over time.

A common inflammatory skin condition that causes flaking, redness, and itching on the scalp. While not a direct cause of permanent hair loss, chronic scalp inflammation associated with seborrheic dermatitis may contribute to shedding. Often managed with antifungal shampoos such as ketoconazole.

A prescription anti-androgen medication used off-label for female pattern hair loss and other androgen-driven conditions. It works by blocking androgen receptors, reducing the effect of DHT on follicles. Not suitable for men due to hormonal side effects. Requires regular monitoring and is prescribed by a licensed clinician.

The delivery of healthcare services — including consultations, prescriptions, and follow-up care — through online platforms. In the context of hair loss, telehealth providers allow patients to consult with licensed clinicians, receive personalized treatment plans, and have prescription medications delivered directly to their door without in-person visits.

A form of diffuse, temporary hair shedding caused by a disruption to the hair growth cycle. Physical or emotional stress, illness, surgery, crash dieting, or hormonal changes push large numbers of follicles into the telogen (resting) phase simultaneously. Shedding typically begins 2–3 months after the trigger and is usually self-resolving. Can unmask or accelerate underlying androgenetic alopecia.

The resting and shedding phase of the hair cycle, lasting approximately 3 months. At the end of telogen, the old hair is shed and a new anagen cycle begins. Roughly 10–15% of scalp hairs are in telogen at any given time. A normal part of the cycle, but an excess of hairs entering telogen simultaneously causes telogen effluvium.

The primary male sex hormone (androgen), present in both men and women. Testosterone itself does not directly cause hair loss, but its conversion to DHT via the 5-alpha reductase enzyme is the key pathway in androgenetic alopecia.

Hair loss caused by repeated or prolonged tension on the hair follicles from tight hairstyles such as braids, weaves, cornrows, or high ponytails. Initially reversible, but can cause permanent follicle damage if the traction continues over time.

A retinoid (vitamin A derivative) that, when included in topical hair loss formulations, enhances scalp penetration of other active ingredients like minoxidil. Prescription-only. Thought to increase minoxidil absorption at the follicle level, potentially improving treatment efficacy. Also has anti-inflammatory effects in the scalp.

Fine, short, lightly pigmented or colorless hairs found across most of the body. In androgenetic alopecia, terminal hairs (thick, pigmented scalp hairs) progressively miniaturize into vellus hairs as follicles shrink in response to DHT. This process is what creates the visual appearance of thinning and eventual baldness.

An essential mineral involved in protein synthesis and cell division — both critical for hair follicle function. Zinc deficiency can contribute to hair shedding and slow regrowth. While supplementation may help in deficient individuals, evidence for benefit in those with normal zinc levels is limited.