Glossary of Hair Restoration Terms

5-alpha reductase is the enzyme that converts testosterone into DHT (dihydrotestosterone). It's the biological trigger behind pattern hair loss in people who are genetically sensitive. Drugs like finasteride and dutasteride work by blocking this enzyme, which is why they're called 5-alpha reductase inhibitors. There are two main types (Type I and Type II), and different medications target them differently.

Androgenetic alopecia is the clinical name for pattern hair loss, the most common type of hair loss in both men and women. It's driven by a combination of genetics and androgens (hormones like DHT). In men, it typically shows up as a receding hairline and crown thinning. In women, it usually presents as diffuse thinning across the top of the scalp. It isn't caused by hats, shampooing too often, or poor circulation.

The anagen phase is the active growth stage of the hair cycle. During this phase, cells in the follicle's root divide rapidly to build the hair shaft. Anagen typically lasts 2-7 years, and the length of your anagen phase determines how long your hair can grow. In people with androgenetic alopecia, the anagen phase progressively shortens, which is why affected hairs get thinner and shorter over time.

ATP is the primary energy molecule that powers virtually every process in your cells, including hair growth. When LLLT (red light therapy) hits the mitochondria in follicle cells, it boosts ATP production, giving those cells more energy to build and maintain hair. Think of ATP as the fuel your follicles burn to do their job. Low cellular energy means sluggish growth; higher ATP means more active follicles.

A biofilm is a thin layer of microorganisms (bacteria, fungi, or yeast) that adheres to the scalp surface and can clog follicles. It's like plaque on your teeth but on your scalp. Research suggests that biofilm buildup may contribute to inflammation around the follicle, worsening conditions like seborrheic dermatitis and potentially accelerating hair loss. Regular exfoliation and targeted scalp treatments can help keep biofilm in check.

The catagen phase is the short transitional period between active growth (anagen) and rest (telogen). It lasts about 2-3 weeks. During catagen, the hair follicle shrinks and detaches from the blood supply. The hair stops growing but doesn't fall out yet. It's a normal and necessary part of the hair cycle, and you can't really speed it up or slow it down with treatments.

Clascoterone (brand name Winlevi) is a topical androgen receptor inhibitor that blocks DHT at the follicle level without the systemic side effects associated with oral finasteride. The FDA approved it for acne in 2020, and clinical trials for androgenetic alopecia are ongoing as of 2026. It's considered promising because it stays local, meaning it doesn't significantly affect hormone levels elsewhere in the body.

Diffuse alopecia refers to hair loss that's spread uniformly across the entire scalp rather than following a pattern like receding temples or a thinning crown. It can be caused by Diffuse Unpatterned Alopecia (DUPA), which is a genetic variant of androgenetic alopecia, Chronic Telogen Effluvium (CTE), nutritional deficiencies, thyroid disorders, or medication side effects. Because it often affects the donor area (sides and back of the head), people with diffuse alopecia may not be ideal candidates for hair transplant surgery.

DHT is the androgen hormone most directly responsible for pattern hair loss. It's created when the enzyme 5-alpha reductase converts testosterone into DHT. In people with a genetic sensitivity, DHT binds to androgen receptors in the hair follicle and triggers miniaturization, gradually shrinking the follicle until it can only produce thin, short, barely visible hair. Blocking DHT (via finasteride, dutasteride, or topical anti-androgens) is one of the most evidence-backed strategies for slowing hair loss.

Exosomes are tiny vesicles (30-150 nanometers) released by cells that carry signaling molecules like growth factors, RNA, and proteins. In hair restoration, exosome therapy involves injecting these vesicles into the scalp to promote follicle regeneration. They're often derived from mesenchymal stem cells. Early clinical data looks promising, but as of 2026, exosome therapy isn't FDA-approved for hair loss and is considered an emerging treatment.

Finasteride is an FDA-approved oral medication that blocks the Type II 5-alpha reductase enzyme, reducing DHT levels by roughly 70%. It's one of the two gold-standard treatments for androgenetic alopecia (the other being minoxidil). Typical dosing is 1mg daily for hair loss. Side effects can include sexual dysfunction in a small percentage of users, which is why topical formulations have gained popularity. It won't regrow a bald scalp, but it's highly effective at stopping further loss and thickening existing hair.

Follicle miniaturization is the hallmark process of androgenetic alopecia. Over successive hair cycles, DHT causes the hair follicle to physically shrink. Each time the follicle cycles, it produces a thinner, shorter, lighter hair than the one before. Eventually, the follicle miniaturizes to the point where it only produces vellus hair (peach fuzz) or stops producing visible hair altogether. Catching miniaturization early is crucial because treatments are far more effective on miniaturizing follicles than on fully dormant ones.

FUE is a hair transplant technique where individual follicular units (groups of 1-4 hairs) are extracted one by one from a donor area (usually the back and sides of the head) and transplanted to thinning areas. Unlike the older FUT (strip) method, FUE doesn't leave a linear scar, which makes it popular with people who wear their hair short. Modern FUE can be performed manually or with robotic assistance (like the ARTAS system). Recovery is typically faster than FUT, but it can take 12-18 months to see the full results.

GT20029 is an experimental topical treatment currently in clinical trials for androgenetic alopecia. It uses PROTAC (Proteolysis Targeting Chimera) technology to selectively degrade the androgen receptor in the scalp rather than just blocking it. Early-phase data from 2025-2026 trials suggests it may offer the anti-androgenic benefits of finasteride without systemic hormonal effects. It's one of the most closely watched pipeline treatments in hair restoration right now.

JAK (Janus Kinase) inhibitors are a class of drugs that suppress specific immune signaling pathways. They've shown dramatic results in alopecia areata, an autoimmune form of hair loss where the immune system attacks hair follicles. Drugs like baricitinib (Olumiant) and ritlecitinib (Litfulo) received FDA approval for alopecia areata. They're not currently approved for androgenetic alopecia, but researchers are exploring whether they could help in cases where inflammation plays a role.

LLLT, also known as photobiomodulation, uses red or near-infrared light (typically 650-670nm) to stimulate cellular activity in hair follicles. The light is absorbed by cytochrome c oxidase in the mitochondria, which triggers increased ATP production and improved blood flow. Multiple FDA-cleared devices are available as caps, helmets, and bands. LLLT won't reverse complete baldness, but clinical studies show it can improve hair density and thickness in people with active miniaturization.

The Ludwig Scale is the standard classification system for female pattern hair loss. It divides hair loss into three stages: Stage I (mild diffuse thinning on top), Stage II (noticeable widening of the part line with decreased volume), and Stage III (extensive thinning across the crown with visible scalp). Unlike the Norwood Scale used for men, the Ludwig Scale doesn't track hairline recession because women typically don't lose their frontal hairline.

Mesenchymal stem cells (MSCs) are multipotent cells that can differentiate into various tissue types. In hair restoration, they're interesting because they secrete growth factors and exosomes that can potentially reactivate dormant follicles. MSC-derived treatments (injections or topicals) are being studied in multiple clinical trials as of 2026. They're part of the broader regenerative medicine approach to hair loss, but they're not yet available as an FDA-approved treatment.

Minoxidil is an FDA-approved topical (and now oral) treatment for hair loss. Originally developed as a blood pressure medication, it was found to stimulate hair growth as a side effect. It works primarily by prolonging the anagen (growth) phase and increasing blood flow to the follicle. Available over the counter in 2% and 5% topical solutions and foams. Extended-release oral formulations are gaining traction in 2026 for patients who don't respond well to topicals. It's effective for both men and women.

The Norwood Scale (also called the Hamilton-Norwood Scale) is the standard classification system for male pattern hair loss. It ranges from Stage 1 (no significant loss) to Stage 7 (extensive loss with only a horseshoe-shaped band of hair remaining). Doctors use it to assess the severity of hair loss and guide treatment recommendations. Knowing your Norwood stage helps you set realistic expectations for what treatments can and can't do.

A nutraceutical is a supplement that delivers bioactive compounds intended to provide health benefits beyond basic nutrition. In the hair loss world, popular nutraceuticals include Nutrafol, Viviscal PRO, and various marine collagen formulations. They typically combine ingredients like saw palmetto, ashwagandha, biotin, and marine-derived peptides. They're not drugs, so they don't require a prescription, but the best ones are backed by clinical studies showing measurable improvements in hair density.

Peptides are short chains of amino acids that act as signaling molecules in the body. In hair care, peptides like copper peptides (GHK-Cu), thymosin beta-4, and various proprietary blends are used in topical serums to signal follicles to enter or stay in the growth phase. They don't work like drugs; instead, they mimic the body's natural growth signals. Peptide-based hair serums from brands like Omi and The Ordinary have become popular as part of multi-modal treatment protocols.

Photobiomodulation (PBM) is the scientific term for using specific wavelengths of light to trigger biological changes in tissue. When people say "red light therapy" or "LLLT" for hair, they're talking about photobiomodulation. The mechanism works through light absorption by chromophores in the mitochondria, which increases cellular energy output. PBM isn't limited to hair; it's used in wound healing, pain management, and dermatology. For hair, wavelengths in the 650-670nm range have the strongest evidence.

PRP therapy involves drawing a small amount of your blood, spinning it in a centrifuge to concentrate the platelets, and then injecting that concentrated plasma into the scalp. Platelets contain growth factors that can stimulate follicle activity and promote healing. It's typically done in-office every 3-6 months. PRP isn't FDA-approved specifically for hair loss, but it's one of the most widely used regenerative treatments. Results vary, and it tends to work best as part of a combination protocol rather than a standalone treatment.

The scalp microbiome is the community of bacteria, fungi, and other microorganisms that live on your scalp. A balanced microbiome supports a healthy scalp environment, while an imbalanced one can contribute to inflammation, dandruff, seborrheic dermatitis, and potentially accelerated hair loss. Research in 2025-2026 has increasingly linked microbiome health to hair follicle function. Harsh shampoos, over-washing, and antibiotics can disrupt the scalp microbiome, which is why gentle, pH-balanced scalp care matters.

Telogen effluvium is a temporary form of hair loss caused by a shock to the system, such as surgery, high fever, severe stress, crash dieting, or hormonal changes (like postpartum). It pushes a large number of follicles into the telogen (resting) phase at the same time, causing noticeable shedding 2-3 months after the triggering event. The good news is it's almost always reversible once the underlying cause is addressed. It's important not to confuse telogen effluvium with androgenetic alopecia, as the treatment approach is completely different.

The telogen phase is the resting stage of the hair cycle, lasting about 2-4 months. During telogen, the hair doesn't grow but stays anchored in the follicle. At the end of telogen, the old hair sheds as a new anagen hair pushes it out. At any given time, about 10-15% of your hairs are in telogen. When that percentage jumps significantly (due to stress, illness, or medication), you get telogen effluvium.

Traction alopecia is hair loss caused by repeated physical pulling or tension on the hair. It's commonly associated with tight hairstyles like ponytails, braids, buns, cornrows, or extensions worn over long periods. The constant tension damages the follicle over time. If caught early, it's fully reversible by changing hairstyles and reducing tension. If the pulling continues for years, the damage can become permanent as the follicles scar over. It's one of the few types of hair loss that's entirely preventable.

VCSEL stands for Vertical-Cavity Surface-Emitting Laser. Unlike traditional edge-emitting laser diodes that shoot a narrow beam, VCSELs emit light from the top surface of the chip in a wider, more uniform cone. In LLLT devices, this means better light distribution across the scalp with fewer hot spots and dead zones. The Xtrallux TurboPro is one of the first hair devices to use VCSEL technology. It's newer and more expensive, but the improved coverage pattern is a genuine technical advantage.

Vellus hairs are the fine, short, nearly colorless hairs that cover most of your body. They're sometimes called "peach fuzz." In the context of hair loss, vellus hairs are significant because follicle miniaturization gradually converts thick terminal hairs into thin vellus hairs. Seeing vellus hairs where you once had thick hair is a sign of active miniaturization. The goal of most treatments is to reverse this process and convert vellus hairs back into terminal hairs, which is possible if the follicle hasn't fully shut down.