The Science of Dual-Wavelength Photobiomodulation

Hair restoration is entering a more biologically precise era, one focused not only on stimulating growth but on optimizing the cellular environment that allows the follicle to function. Photobiomodulation offers a nonpharmacologic approach to support this process by influencing mitochondrial activity, adenosine triphosphate (ATP) production, oxidative stress, inflammatory signaling, microcirculation, and follicular cycling. This concept is particularly relevant because the hair follicle is a highly energy-dependent mini-organ, and successful regeneration depends on more than a single growth signal.

At the same time, not all light-based therapies are equivalent. Clinical outcomes depend on variables such as wavelength, power, fluence, treatment timing, depth of penetration, and the tissue’s biologic response. Dual-wavelength platforms may be particularly useful in clinical practice because they can target both superficial and deeper follicular structures, including the vascular network and cellular niches involved in hair growth. In practice, photobiomodulation may serve as a valuable adjunct before and after regenerative treatments such as platelet-rich plasma (PRP), microneedling, polydeoxyribonucleotide (PDRN), and exosome-based therapies, helping create a more receptive scalp environment for stronger, healthier, and more resilient hair growth.

THE MITOCHONDRIAL FOUNDATION

Every red-light therapy device on the market relies on the same foundational biology. Photons in the red and near-infrared range are absorbed by cytochrome c oxidase (CCO), complex IV of the mitochondrial electron transport chain. Inhibitory nitric oxide (NO) bound to the enzyme is dissociated by the photon energy, electron transport resumes, mitochondrial membrane potential rises, and ATP production increases. This is the canonical photobiomodulation pathway, reviewed comprehensively by de Freitas and Hamblin in their 2016 paper titled “Proposed Mechanisms of Photobiomodulation or Low-Level Light Therapy.”¹

Released nitric oxide does not simply remain localized. It diffuses out of the mitochondria and into the surrounding tissue, where it acts as a potent vasodilator, relaxing perifollicular vasculature and increasing oxygen and nutrient delivery to the dermal papilla. Wolf and colleagues showed in 2003 that human dermal papilla cells already use NO as a native signaling molecule, with both constitutive endothelial nitric oxide synthase (eNOS) and dihydrotestosterone (DHT)-inducible NO synthase expression, confirming NO is not an exogenous insult but part of the follicle’s normal physiology.²

Every legitimate low-level light therapy (LLLT) device shares this foundational biology involving NO and photobiomodulation, but this mechanism explains only blood flow.

THE 620-NM DIFFERENTIATOR

In a 2025 Journal of Biophotonics paper, Kocher and colleagues demonstrated that the combination of 620-nm and 660-nm light drives the production of NO and a controlled burst of reactive oxygen species (ROS) sufficient to inhibit 5-α reductase, the enzyme that converts testosterone to DHT.³

The mechanism involves NO being released by the dual-wavelength stimulus, which appears to nitrosate a critical, highly conserved thiol residue in the active site of 5-α reductase, inactivating it. In A549 and HEK293T cell lines and a cell-free NO release platform, the dual-wavelength combination reduced DHT production by 79%—comparable to roughly 1 µM finasteride, and more than double the ~38% reduction finasteride achieved in the same in vitro experiment.³

The 620-nm wavelength is the spectral component that drives the NO/ROS dynamics necessary to suppress 5-α reductase activity. Analogously, a single-wavelength cap is like striking a single piano key to produce a clean, simple tone (vasodilation, modest ATP boost), whereas the dual-wavelength system strikes a chord for the same vasodilation effect while a second, harmonic mechanism (DHT inhibition) fundamentally changes what the device can credibly claim to do biologically.

A critical caveat for honest physician communication: the 79% DHT reduction figure is from in vitro work. It is mechanistic proof of concept, not yet confirmed by direct DHT measurement in treated patient scalp tissue. However, full-thickness scalp biopsies are not being done anywhere on healthy androgenetic alopecia (AGA) patients to prove this in vivo, and rodent studies in this space have a notoriously poor track record of human translation. Still, the in vitro mechanistic paper is paired with clinical efficacy data showing the dual-wavelength photobiomodulation grows hair in real patients. 

THE INFLAMMATION AXIS

The third leg of the AGA pathophysiology stool is perifollicular microinflammation—the chronic low-grade inflammatory signaling that contributes to follicle miniaturization independent of pure DHT effects. Photobiomodulation has well-established anti-inflammatory effects mediated through NF-κB modulation, cytokine downregulation, and resolution of oxidative stress in chronically inflamed tissue.¹ Combined with the vasodilatory and DHT-inhibitory effects, this provides a 3-pathway story: blood flow, DHT, and inflammation, all addressed simultaneously through one 10-minute daily home treatment.

THE CLINICAL EVIDENCE FOR DUAL-WAVELENGTH PHOTOBIOMODULATION

Although it is important to appreciate the mechanism behind photobiomodulation, the real clinical question is whether hair actually grows.

In the REVIAN 101 prospective, randomized, double-blind, placebo-controlled trial (NCT04019795), published by Thomas and colleagues in Dermatologic Surgery (2025),^4,5 compliant subjects (≥80% adherence) demonstrated an increase of 26.3 hairs/cm2 at 16 weeks compared to placebo using a dual-wavelength photobiomodulation device (Revian Red, Revian). There were no treatment discontinuations due to adverse events and no device-related serious adverse events. The compliance-response gradient was clean and dose-dependent, plateauing around 80% adherence, likely due in part to an integrated app-based compliance tracking feature. Overall, the results of the trial were a net gain as the active group grew new hair while the placebo group continued the slow loss characteristic of untreated AGA.

THE 620-NM STORY

If 620 nm is the critical wavelength for NO-driven 5-α reductase inhibition,³ why do no US Food and Drug Administration (FDA)-cleared laser caps include it?

The answer is materials science. Commercial visible red laser diodes are manufactured almost exclusively from the aluminum gallium indium phosphide (AlGaInP) semiconductor system, which operates efficiently from ~630-760 nm, clustering at 650, 655, 670, and 680 nm. Every laser cap on the market sits in that window. Below ~630 nm, AlGaInP laser performance collapses, thresholds spike, thermal stability fails, and yields plummet. A commercially viable 620-nm laser diode for a hair device does not exist.

Light-emitting diodes (LEDs) have no such limitation. The same AlGaInP material, configured as an LED, emits cleanly at 620 nm. Accordingly, only LEDs can practically deliver the dual-wavelength (620 + 660 nm) architecture paired with the demonstrated NO/ROS dynamics that inhibit DHT production.

THE CLINICAL IMPACT OF DUAL-WAVELENGTH PHOTOBIOMODULATION

Dual-wavelength architecture can target all 3 established pathogenic drivers—DHT, inflammation, and microcirculation—through NO signaling. It is non-systemic, has essentially no drug interactions, and stacks cleanly with treatments involving topical minoxidil, oral 5-α reductase inhibitors, PRP, and exosomes, as well as pre/post-operatively around hair transplant. For patients hesitant about finasteride’s sexual side effect profile, for women whose options are largely limited to topical minoxidil, for younger prevention-stage patients, and for patients receiving glucagon-like peptide-1 receptor agonists worried about shedding, this technology sits in a uniquely defensible position.

The mechanistic evidence is strong but appropriately framed: vasodilation via NO is well-established in vivo across the photobiomodulation literature; and DHT inhibition is a compelling in vitro finding awaiting in vivo confirmation. The clinical trial demonstrates the device grows hair.

In the ongoing pursuit of nonpharmacologic therapies for hair restoration with minimal side effect profiles, photobiomodulation can be a strong adjunct to many of the treatments already being performed in clinic. 

1. de Freitas LF, Hamblin MR. Proposed Mechanisms of Photobiomodulation or Low-Level Light Therapy. IEEE J Sel Top Quantum Electron. 2016;22(3):7000417. PMID: 28070154. https://pubmed.ncbi.nlm.nih.gov/28070154/

2. Wolf R, Schönfelder G, Paul M, Blume-Peytavi U. Nitric oxide in the human hair follicle: constitutive and dihydrotestosterone-induced nitric oxide synthase expression and NO production in dermal papilla cells. J Mol Med (Berl). 2003 Feb;81(2):110-7. doi:10.1007/s00109-002-0402-y. PMID: 12601527. https://pubmed.ncbi.nlm.nih.gov/12601527/

3. Kocher J, Jones N, Stallings D, et al. Dual Wavelength LEDs Induce Reactive Oxygen Species and Nitric Oxide That Inhibit the Production of Dihydrotestosterone by 5-α Reductase. Journal of Biophotonics. 2025. doi:10.1002/jbio.202400388. https://onlinelibrary.wiley.com/doi/10.1002/jbio.202400388

4. Thomas M, Stockslager M, Oakley J, Womble TM, Sinclair R. Clinical Safety and Efficacy of Dual Wavelength Low-Level Light Therapy in Androgenetic Alopecia: A Double-Blind Randomized Controlled Study. Dermatol Surg. 2025 Apr 1;51(4):416-421. doi:10.1097/DSS.0000000000004509. PMID: 39679573. https://pubmed.ncbi.nlm.nih.gov/39679573/

5. REV-01 Clinical Trial. Modulated Light Therapy in Participants With Pattern Hair Loss. ClinicalTrials.gov Identifier: NCT04019795. https://clinicaltrials.gov/study/NCT04019795

Disclosure: Dr. Plews is a Scientific Advisor for Revian.