The active growth phase of the hair follicle cycle — the period during which the hair shaft is actively being produced and lengthened. Anagen duration varies by follicle and individual, typically lasting 2–7 years on the scalp. The longer the anagen phase, the longer the hair can grow.

Red light therapy (LLLT) is believed to extend the anagen phase, keeping follicles in active growth for longer. See: Complete Guide to Red Light Therapy.

The most common form of hair loss in both men and women, driven by a genetic predisposition to DHT sensitivity. In men, it follows the Norwood pattern (temples and crown). In women, it typically presents as diffuse thinning at the part line and crown (FPHL).

Androgenetic alopecia is the primary indication for LLLT with the strongest evidence base. See: Men's Hair Wellness Guide and Women's Hair Wellness Guide.

An autoimmune condition in which the immune system attacks hair follicles, causing patchy, discrete bald spots rather than the diffuse thinning characteristic of androgenetic alopecia. The cause is different from MPB — it is not DHT-driven.

LLLT evidence for alopecia areata is more limited than for AGA. Consult a dermatologist before using any device for this condition.

The primary energy currency of cells — the molecule that powers virtually all cellular processes. ATP is produced in the mitochondria through the electron transport chain.

The leading mechanism by which red light therapy supports follicle function: 650–660nm light is absorbed by cytochrome c oxidase (the final enzyme in the electron transport chain), which increases ATP production. More ATP means more cellular energy available for follicle activity.

The stimulation of biological processes through external energy — including light energy. In the context of scalp wellness, biostimulation refers to the cellular responses triggered by LLLT: increased ATP production, improved microcirculation, and reduced inflammation.

The transition phase of the hair growth cycle — a brief period (2–3 weeks) between active growth (anagen) and rest (telogen) during which the follicle detaches from its blood supply and the hair shaft stops growing. Approximately 3% of scalp hairs are in catagen at any given time.

Light in which all photons travel in phase, in the same direction, at the same wavelength. This is the defining characteristic of laser light — as opposed to LED light, which is non-coherent (photons scatter in multiple directions).

Coherent light maintains its energy density more effectively as it penetrates tissue, delivering more concentrated photon energy to follicle depth. See: LED vs. Laser Guide.

The primary photoacceptor in the LLLT mechanism — an enzyme in the mitochondrial electron transport chain that absorbs red and near-infrared light (particularly at 630–680nm and 820–870nm). When activated by light, it increases electron transfer efficiency, boosting ATP production.

Cytochrome c oxidase is the reason wavelength precision matters: light outside the absorption spectrum of CCO produces no meaningful biological effect in follicle cells.

The layer of skin beneath the epidermis, approximately 1–4mm deep. Most hair follicle bulbs are located in the reticular dermis (the deeper portion), making this the primary target depth for scalp wellness devices. Red light at 650–660nm penetrates to approximately 2–4mm — reaching the dermis and follicle bulbs when delivered by a quality device with good scalp contact.

A potent androgen derived from testosterone via the enzyme 5-alpha reductase. DHT binds to androgen receptors in genetically susceptible follicles, causing progressive miniaturization — shortening the growth cycle, thinning the hair shaft, and eventually causing follicle dormancy.

DHT is the primary hormonal driver of androgenetic alopecia in both men and women. Finasteride and dutasteride work by inhibiting 5-alpha reductase, reducing DHT production.

A prescription 5-alpha reductase inhibitor that suppresses both type 1 and type 2 5-alpha reductase — producing stronger DHT reduction than finasteride, which inhibits type 2 only. Used off-label for androgenetic alopecia. Requires physician supervision.

The shedding phase of the hair cycle — when the old hair shaft is actively shed from the follicle. Exogen follows telogen (resting phase) and precedes the next anagen cycle. Normal daily shedding of 50–100 hairs is largely exogen activity. Increased exogen activity is what users notice as "shedding" — which can temporarily increase at the start of LLLT or minoxidil treatment as follicles cycle.

A prescription 5-alpha reductase type 2 inhibitor that reduces DHT production by approximately 70%. The most widely prescribed oral medication for male androgenetic alopecia. Works through a different mechanism than LLLT or minoxidil, making it complementary in combination protocols.

Requires medical supervision. Not recommended for women who are pregnant or may become pregnant. See: Men's Hair Wellness Guide.

The tubular structure in the skin that produces a hair shaft. Each follicle cycles independently through anagen, catagen, telogen, and exogen phases. A human scalp contains approximately 100,000 follicles. Follicle health — including its blood supply, cellular energy, and DHT sensitivity — determines hair growth quality and longevity.

The female expression of androgenetic alopecia. Unlike the male pattern (temporal recession and crown baldness), FPHL typically presents as diffuse thinning across the crown and widening of the part line, with the frontal hairline largely preserved. Driven by similar DHT sensitivity as MPB, but modulated by oestrogen levels.

See: Women's Hair Wellness Guide.

The four-phase cycle through which each hair follicle operates: Anagen (growth) → Catagen (transition) → Telogen (rest) → Exogen (shedding). The full cycle takes approximately 3–7 years on the scalp. LLLT is believed to support the cycle by extending anagen, shortening telogen, and improving the follicle environment during each phase.

The power of light delivered per unit area — measured in milliwatts per square centimetre (mW/cm²). Irradiance is the key metric for understanding how much therapeutic light energy a device delivers to the scalp surface per second. Combined with session duration, irradiance determines the total dose (fluence) received per session.

Higher irradiance is not always better — there is an optimal dose window, above which photoinhibition (reduced biological response) can occur.

An antifungal agent available in shampoo form (typically 1–2%) that has shown evidence for reducing scalp DHT levels and improving hair density when used regularly. Often used as part of a multi-modal hair wellness approach alongside LLLT and minoxidil. Fully compatible with red light therapy — use on wash days and ensure scalp is fully dry before LLLT sessions.

A device that produces coherent light through the process of stimulated emission — photons with the same phase, direction, and wavelength. In scalp wellness devices, laser diodes (typically at 650nm) are used to deliver focused, phase-aligned light to follicle depth more efficiently than LED light.

See: LED vs. Laser Guide.

A semiconductor device that produces light through electroluminescence — photons are emitted in multiple directions at slightly varying wavelengths (non-coherent light). LEDs are used in scalp wellness devices for their cost efficiency (allowing high diode counts) and multi-spectrum capability. The 7hw StrandAir uses 108 LEDs at 660nm + 850nm.

The clinical term for the application of low-power laser or LED light to biological tissue for therapeutic effect. In scalp wellness, LLLT refers to the use of 630–670nm red light (and sometimes 820–870nm near-infrared) to stimulate follicle cell activity, improve scalp microcirculation, and support the hair growth cycle.

Also called photobiomodulation (PBM). The basis of all three 7hw Strand devices. See: Complete Guide.

A scalp treatment using a dermaroller or derma-pen to create controlled micro-injuries in the scalp, triggering growth factor release and potentially improving topical product absorption. Compatible with LLLT but should not be done on the same day — allow 48 hours recovery before resuming light therapy sessions.

The progressive reduction in follicle size and output caused by DHT sensitivity — the core mechanism of androgenetic alopecia. Miniaturization produces increasingly fine, short hair shafts from affected follicles over successive growth cycles, eventually resulting in vellus hairs (fine, colourless) and then follicle dormancy.

LLLT is most effective on miniaturized but still-active follicles. Fully dormant, atrophied follicles are unlikely to respond.

A vasodilatory agent (originally developed as an oral blood pressure medication) that promotes hair growth by opening potassium channels in follicle cells, increasing blood flow, and extending the anagen phase. Available in topical (2%, 5%) and oral formulations. Works through a different mechanism than LLLT, making the two treatments genuinely complementary.

See: Red Light + Minoxidil Guide.

The organelles within cells responsible for producing ATP through the electron transport chain. The primary site of LLLT's biological action — red light at 650–660nm activates cytochrome c oxidase, a key enzyme in the mitochondrial electron transport chain, increasing ATP output.

The male expression of androgenetic alopecia. Characterised by a predictable pattern of temporal recession and crown thinning (classified using the Norwood scale). Driven by DHT sensitivity in genetically predisposed follicles. Affects approximately 50% of men by age 50.

See: Men's Hair Wellness Guide.

Light in the 820–870nm wavelength range — invisible to the human eye, but biologically active in tissue. NIR penetrates deeper than visible red light (up to 5–10mm), reaching subcutaneous tissue. Benefits include reduced inflammation, improved microcirculation, and deeper tissue support.

The 7hw StrandAir includes 850nm NIR alongside 660nm red — the only device in the Strand series with dual-spectrum NIR coverage.

A signalling molecule released by cells in response to LLLT. Nitric oxide causes vasodilation — the widening of blood vessels — which improves microcirculation in the scalp. This increases oxygen and nutrient delivery to follicles, complementing the direct ATP-boosting effects of red light at the cellular level.

The Norwood-Hamilton scale — a seven-stage classification of male pattern baldness, from Stage I (no visible recession) to Stage VII (extensive loss retaining only a side fringe). Used clinically to assess severity and treatment suitability. LLLT shows strongest results at Norwood Stages I–IV; response decreases at Stages V–VII as follicles atrophy.

See: Men's Hair Wellness Guide.

The umbrella term for the use of light to modulate biological function. PBM includes LLLT as a specific application, but also encompasses near-infrared and other wavelength applications. All three 7hw Strand devices are photobiomodulation devices. Also called low-level light therapy (LLLT), soft laser therapy, or biostimulation.

The opposite of biostimulation — the suppression of biological activity when light dose exceeds the optimal therapeutic window. Longer or more frequent sessions than recommended do not produce better results; at excessive doses, cell activity can be inhibited rather than stimulated. This is why all 7hw Strand devices include auto-timers set to the recommended session duration.

A clinical treatment in which the patient's own blood plasma (concentrated with platelets and growth factors) is injected into the scalp to stimulate follicle activity. PRP is typically administered in-clinic every 3–6 months. Compatible with LLLT — skip your light therapy session on PRP day and for 48 hours afterward, then resume normally.

The network of small blood vessels (capillaries) that supply the scalp and hair follicles with oxygen and nutrients. Poor scalp microcirculation — common in areas of established thinning — reduces follicle vitality. LLLT promotes nitric oxide release, causing vasodilation that improves microcirculation in treated areas.

A temporary increase in hair shedding that can occur in the first 4–8 weeks of starting LLLT or minoxidil. Caused by follicle cycling — dormant telogen hairs being shed to make way for new anagen growth. It is a sign that the treatment is active, not that it is causing damage. The shedding phase typically resolves within 8–12 weeks with consistent use.

The resting phase of the hair growth cycle — typically lasting 2–3 months — during which the follicle is dormant and the hair shaft is retained but not growing. Approximately 10–15% of scalp hairs are in telogen at any given time. At the end of telogen, the follicle either re-enters anagen or proceeds to exogen (shedding).

A form of diffuse, whole-scalp shedding triggered by a physiological or psychological stressor — most commonly post-partum hormonal shifts, illness, surgery, significant nutritional deficiency, or high psychological stress. Unlike androgenetic alopecia, TE is usually temporary and self-resolving over 6–12 months. LLLT may support follicle recovery during the TE period.

See: Women's Hair Wellness Guide.

Thick, pigmented, fully-developed hair — as opposed to vellus hair (fine, unpigmented). In androgenetic alopecia, the miniaturization process converts terminal hairs to progressively thinner hairs and eventually to vellus hairs. One of the goals of LLLT and minoxidil is to support the conversion of vellus hairs back toward terminal hair thickness.

The widening of blood vessels, increasing blood flow to surrounding tissue. Both LLLT (via nitric oxide release) and minoxidil (via potassium channel activation) produce vasodilation in the scalp — improving nutrient and oxygen delivery to follicles. This is one reason the two treatments are synergistic: they produce vasodilation through different signalling pathways.

Short, fine, lightly pigmented hair produced by miniaturized follicles — as opposed to terminal hair. The presence of vellus hairs in a thinning area indicates that the follicle is still alive but miniaturized. This is an important indicator of LLLT candidacy: vellus hairs suggest viable follicles that may respond to stimulation. Smooth, follicle-free scalp indicates atrophy rather than miniaturization.

The distance between successive peaks of a light wave — measured in nanometres (nm). Different wavelengths correspond to different colours of light and different tissue penetration depths. For scalp wellness, the two therapeutic windows are 630–670nm (visible red — follicle stimulation) and 820–870nm (near-infrared — deeper tissue support and anti-inflammation).

Wavelength precision is critical: a device that doesn't specify its nm output — or uses wavelengths outside the therapeutic window — will not produce the same biological effects. See: Complete Guide.