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Photobiomodulation, without the hype.
Your patients are already asking about red-light devices. In seven short chapters, this masterclass walks you through the evidence: what photobiomodulation is, what the thyroid trials found, and how to answer the question across the desk.
- What photobiomodulation actually is
- Mechanisms of action
- The thyroid evidence base
- Wavelengths, dose & the biphasic curve
- Systemic & metabolic angles
- Talking to patients about red light
- Evidence gaps & the honest bottom line
Built on the published research
Every claim in this masterclass traces back to peer-reviewed work, with the primary sources cited so you can read them yourself. Here are four of the key papers.
Written for the clinician who'd rather be skeptical
Photobiomodulation has a credibility problem. The research sits under wellness hype, influencer claims and overpriced panels. This primer is sober and sourced, so you can assess the evidence yourself in under an hour.
The mechanism, properly
How red and near-infrared light interacts with the mitochondria, explained well enough to defend in front of a colleague.
The thyroid evidence, honestly
What the Höfling trials measured, what they didn't, their sample sizes, and where the gaps are, including the inconvenient parts.
The patient conversation
A clear, calm answer to "Doctor, should I buy one of these?" that separates wellness use from medical claims.
From first principles to the patient conversation
Chapter 1: What photobiomodulation actually is
The definition, the history, and the "optical window": why light between about 600 and 900 nm reaches into tissue and has a measurable effect without heating it.
Chapter 2: Mechanisms of action
Cytochrome c oxidase, the electron transport chain, ATP, nitric oxide release, reactive oxygen species as signalling, and the intracellular-melatonin story. Why more is not better: the biphasic dose-response.
Chapter 3: The thyroid evidence base
The endocrinology chapter. The Höfling 830 nm trials in autoimmune thyroiditis, read critically: design, endpoints (TPOAb, levothyroxine dependence, ultrasound echogenicity), the 2013 RCT, the 2018 follow-up, and their limitations.
Chapter 4: Wavelengths, dose & the biphasic curve
Irradiance, fluence and energy: the parameters that decide whether studies are comparable. The dose ranges the trials used, the ~15 minute "switch", coherence (laser vs. LED), and safety. A report of the literature, not a protocol.
Chapter 5: Systemic & metabolic angles
Why light applied to one area can show up in systemic readouts: Jeffery's glucose work, mitochondrial signalling and exhaled-CO₂ markers. And where photobiomodulation fits in the metabolic-health conversation your patients are already having.
Chapter 6: Talking to patients about red light
The practical chapter. "It's nonsense" costs you trust; "sure, it cures things" costs you credibility. A calibrated script for the consult: what counts as a reasonable wellness adjunct, what counts as a medical claim, and where to draw the line.
Chapter 7: Evidence gaps & the honest bottom line
Where the research is thin, what would change your mind, the trials we still need, and a one-paragraph summary you could hand a colleague.
Chapter 1: What photobiomodulation actually is
Start with the word, because it tells you everything. Photo: light. Bio: life. Modulation: to adjust, up or down. Photobiomodulation (PBM) is the use of light to adjust biological activity at the cellular level. Note what the word does not say: it doesn't say "heat," it doesn't say "burn," it doesn't say "destroy." That distinction is the whole subject.
Most clinical light you already know is ablative or thermal: a surgical laser cuts, an IPL device heats. PBM operates at intensities far below that threshold. The light is absorbed, a cellular response follows, and the tissue is not damaged. The older name, low-level laser therapy, caused decades of confusion, because "laser" implied danger and "low-level" implied "probably nothing." The field renamed itself photobiomodulation in 2014 for exactly that reason.
Why a specific band of light, and not just "light"
Shine a torch at your palm in a dark room and you'll see a red glow come through the other side. That is the entire premise, made visible. Tissue is not uniformly opaque. Its two dominant absorbers, haemoglobin and water, each have wavelengths they swallow and wavelengths they let pass.
Haemoglobin absorbs strongly in the blue and green. Water absorbs strongly in the longer infrared. Between them sits a relatively transparent gap, roughly 600 to 900 nanometres, spanning red and near-infrared, where light penetrates living tissue most effectively. This gap has a name: the optical window. Everything in this masterclass lives inside it.
Penetration follows wavelength
Inside the window, a simple rule holds: longer wavelength, deeper penetration. Red light around 630 to 660 nm acts largely at the skin and just beneath it; near-infrared around 800 to 850 nm reaches centimetres deeper. A useful analogy from physician Roger Seheult: the bass from a passing car travels far while the treble fades fast. Same physics, longer wavelengths carry further. It's also why near-infrared is invisible: your eye's receptors stop at roughly 700 nm, so a device can be flooding tissue with 830 nm light while looking, to you, switched off.
Photobiomodulation is non-thermal light in the ~600 to 900 nm "optical window" used to adjust cellular activity, not to heat or ablate tissue. Within that window, longer (near-infrared) wavelengths penetrate deeper than visible red. Hold onto this; Chapter 2 explains what the light actually does once it arrives.
Why this matters to an endocrinologist specifically
The thyroid is a superficial, highly vascular gland sitting one to two centimetres below the skin of the anterior neck, squarely within reach of light in the optical window. That anatomical accessibility is precisely why a small cluster of research groups have studied light over the thyroid at all, and why your patients are increasingly arriving with a red-light gadget already in their cart. The next two chapters give you the mechanism and then the actual thyroid trials.
- Anders JJ, Lanzafame RJ, Arany PR. Low-level light/laser therapy versus photobiomodulation therapy. Photomed Laser Surg. 2015 (the 2014 naming consensus).
- Hamblin MR. Mechanisms and applications of the anti-inflammatory effects of photobiomodulation. AIMS Biophys. 2017 (on the optical window and tissue optics).
Mechanisms of action
In Chapter 1 we said photobiomodulation adjusts what a cell is doing. This chapter is the how, and it comes down to one protein, sitting at the very end of the energy-production line.
The antenna: cytochrome c oxidase
Inside every mitochondrion runs the electron transport chain, the assembly line that makes ATP. Its fourth and final station is an enzyme called cytochrome c oxidase, and it absorbs red and near-infrared light almost perfectly. It is, in effect, the antenna that catches the light. Not by design; the same metal centres that shuttle electrons happen to absorb these wavelengths.
Here's the key event. Under stress (illness, inflammation, ageing), a molecule of nitric oxide can park on cytochrome c oxidase and throttle the line, like a kink in a hose. Absorbed light nudges that nitric oxide off. The kink releases, electron flow resumes, oxygen is used more efficiently, and ATP output rises.
Two more effects worth knowing
Alongside it, the light triggers a brief, small burst of reactive oxygen species. In large amounts these are damaging (that's oxidative stress), but in this small, controlled dose they act as a signal, switching on protective genetic programmes that leave the cell more resilient. The same principle as exercise: a little controlled stress makes the system stronger.
And a third, more recent piece. Work by Reiter and Zimmerman shows near-infrared light prompts the mitochondria to make their own melatonin: not the pineal melatonin that makes you sleepy, but a subcellular melatonin made inside the cell, acting as a powerful local antioxidant that mops up the very oxidative stress energy production creates.
More is not better. The response is biphasic: too little does nothing, the right amount helps, too much suppresses the effect (the Arndt-Schulz curve). It's why serious devices use modest intensity and short sessions, not maximum power. Carry that curve in your head; it's what most marketing gets wrong.
One connection for you as an endocrinologist: thyroid follicular cells are metabolically demanding and mitochondria-rich, so a mechanism acting on mitochondrial efficiency is at least biologically plausible there. That is the cue for the next chapter, where we look at what actually happened when researchers tried it.
- Hamblin MR. Mechanisms and applications of the anti-inflammatory effects of photobiomodulation. AIMS Biophys. 2017.
- Zimmerman S, Reiter RJ. Melatonin and the optics of the human body. Melatonin Research. 2019.
The thyroid evidence base
This is the chapter you came for: not the mechanism, not the marketing, but the actual human data on light over the thyroid. It centres on one body of work: a group in São Paulo led by Danilo Höfling.
The trial that put it on the map
Published in 2013: a randomized, placebo-controlled study in patients with hypothyroidism caused by chronic autoimmune thyroiditis (Hashimoto's). Around 43 patients, all first brought into a stable euthyroid state on levothyroxine, were randomized to ten sessions of near-infrared light over the thyroid at 830 nm, or to a placebo device that felt identical. The levothyroxine was then carefully withdrawn and patients followed to see what their own thyroids could do.
Read plainly, the results: the light group needed less levothyroxine afterwards to stay euthyroid (some none, for a period); TPO antibodies fell in the treated group; and on ultrasound the tissue looked healthier: improved echogenicity and better blood flow on Doppler. A 2018 follow-up reported the benefit was still detectable years later. No significant adverse events were recorded.
Now put your skeptic's hat back on
Because you should. It's a single research group. Samples are small (dozens, not thousands) and largely one centre. Some endpoints are surrogates (antibody levels, medication dose) rather than long-term, patient-felt outcomes. And no large, independent, multicentre trial has yet replicated it. Encouraging is the honest word. Practice-changing is not. Not yet.
There is a real, randomized, placebo-controlled signal that near-infrared light over the thyroid did something measurable in autoimmune thyroiditis, and that it was safe in those studies. That is genuinely more than most people arguing about red light actually know. It is also a long way from established therapy. Both are true at once, and a good clinician can hold them together.
- Höfling DB, et al. Low-level laser in the treatment of patients with hypothyroidism induced by chronic autoimmune thyroiditis: a randomized, placebo-controlled clinical trial. Lasers Med Sci. 2013.
- Höfling DB, et al. Safety and efficacy of low-level laser therapy in autoimmune thyroiditis: long-term follow-up study. Int J Endocrinol. 2018.
Wavelengths, dose & the biphasic curve
If you remember one idea from this chapter, make it this: the dose is the whole game, and most products and most arguments fall apart precisely because nobody specifies it.
The four numbers
Before any claim means anything, pin down: wavelength (nm; sets depth and target); irradiance / power density (mW/cm²; beam intensity at the tissue); time of exposure; and their product, fluence / energy density (J/cm²). Two devices can advertise the same wavelength and deliver wildly different doses. If a study or product won't give you those numbers, you cannot evaluate it. That alone filters out most of the noise.
What did the trials we take seriously use? Höfling's thyroid work used 830 nm at low output (tens of milliwatts) to several points per lobe across ten sessions. Jeffery's mitochondrial studies used 670 nm red. Across the literature, beneficial fluences at the tissue cluster in the low single digits up to ~10 J/cm². Modest doses, not blasts.
Does it have to be a laser?
No. Early work used lasers, but Hamblin and others showed that for photobiomodulation, coherence isn't the active ingredient. An LED at the same wavelength and dose does the same job. That matters, because essentially every consumer red-light device (and increasingly the credible research) uses LEDs.
In the trials, near-infrared over the thyroid was well tolerated with no significant adverse events. General PBM cautions in the literature: eye protection (especially with lasers), awareness of photosensitising medication, and a conservative stance over known nodules or any suspicion of malignancy, and in pregnancy (the data are simply thin). This is the contour of what the published work covers, which is what you need when a patient asks.
- Huang YY, Hamblin MR, et al. Biphasic dose-response in low-level light therapy. Dose-response. 2009.
- de Freitas LF, Hamblin MR. Proposed mechanisms of photobiomodulation / LLLT. IEEE J Sel Top Quantum Electron. 2016 (coherence not essential).
Systemic & metabolic angles
Here's a finding that surprises most clinicians and reframes the whole field: you don't necessarily have to put the light where you want the effect.
The cleanest demonstration is from Jeffery's lab. They shone red light on people's backs (nowhere metabolically special), then measured blood sugar after a glucose drink. The light-exposed group had noticeably smaller spikes, and exhaled CO₂ went up, a fingerprint of mitochondria burning fuel faster. Light on the skin of the back; a measurable change in whole-body glucose handling.
How can a local exposure act systemically? The current thinking: mitochondria aren't isolated batteries. They signal to one another and release factors into the circulation, so improving a population of them in one region can ripple outward. You don't have to illuminate every cell to shift the system.
This makes the biology more interesting (a mitochondrial intervention is plausibly relevant to the metabolic and energy complaints that fill an endocrinology clinic) and the marketing more dangerous, because a grain of real systemic science is exactly what gets stretched into "cures everything." Keep the grain; discard the stretch. Plausible and promising is the right register; established is not.
- Powner MB, Jeffery G. Systemic glucose tolerance improvement after long-wavelength light exposure. 2024 (local exposure, systemic metabolic effect).
Talking to patients about red light
Let's make this concrete, because this is the moment that matters: the patient in front of you, phone in hand, asking whether they should buy a red-light device for their thyroid. Here's a way to answer that keeps both your integrity and their trust.
Don't dismiss it
Dismissal is both inaccurate and a trust-killer. Say, honestly, that there's real science here. Light at these wavelengths does affect the mitochondria, and there have even been small randomized trials over the thyroid with encouraging, safe results. The moment you acknowledge the real part, the patient stops being defensive and starts listening.
Then draw the line clearly
This is where you earn your fee. There's a difference between a wellness adjunct and a medical treatment. As a general-wellness tool (energy, recovery, skin, relaxation), a low-risk red-light device is, for most people, a reasonable thing to try. But it is not a replacement for their levothyroxine, it will not cure their Hashimoto's, and it should never be a reason to stop or reduce prescribed medication on their own. That one boundary prevents almost every way this can go wrong.
Tell them marketing will overclaim. "Cures/treats disease" language is a red flag, not a green one. Keep taking medication, keep blood tests on schedule, so you (not the device's app) stay the one watching their thyroid. Basic eye sense around bright sources. And reassure them that wanting more control over their health is legitimate. Your role is to keep them safe while they explore it.
This positions you not as the gatekeeper who says no, but as the trusted filter who separates the real from the nonsense. In an age of infinite health content, that is the most valuable thing a clinician can be. The patient leaves with medication intact, expectations calibrated, and a stronger relationship with you. Far better than either a flat no or an uncritical yes.
Evidence gaps & the honest bottom line
We finish where good science should: with what we don't know. The fastest way to lose a thoughtful patient or colleague is to oversell; the fastest way to keep their trust is to name the gaps yourself, first.
What's genuinely unsettled
No agreed optimal dose for the thyroid: best wavelength, energy, number and spacing of sessions are open. No large, independent, multicentre trials; the most cited thyroid work is essentially one group with modest numbers. A rich mechanism but a thin bridge to long-term, patient-felt outcomes. We don't know who responds. And, like any field with commercial energy behind it, a real risk of publication and funding bias.
What would move it from interesting to established? Large, well-designed, independent randomized trials with hard endpoints and honest long-term safety data over thyroid tissue, plus proper dose-finding. Until that exists, honesty means holding this as promising rather than proven.
Photobiomodulation is the use of non-thermal red and near-infrared light to improve mitochondrial function; the mechanism is well characterised and the lab science is solid. In the thyroid, small randomized trials in autoimmune thyroiditis have shown encouraging, safe results, but they are small, largely single-centre, and not yet replicated at scale. It is reasonable to regard a low-risk red-light device as a general-wellness option, while being clear it is not an established treatment for any thyroid disease and no substitute for standard care.
That's the honest bottom line: calibration, not hype and not reflexive dismissal. If this masterclass has made you a slightly more confident, slightly more sceptical, better-informed voice on red light when patients ask, it's done its job. Thank you for giving it your time.
Produced by the team behind ThyRed
ThyRed sponsored and produced this masterclass. We make a wearable red & near-infrared light device for the neck. We built this course as education, and there is no "buy now" button in the chapters.
ThyRed rests 80 g on the neck and delivers commonly studied red and near-infrared wavelengths (630 / 660 / 830 nm) for general wellness use, with EMF under 3 mG. It is a wellness device and not a medical device. Nothing in this masterclass should be read as a claim that it diagnoses, treats, or prevents any condition.
This masterclass is educational content for healthcare professionals. It summarises third-party, peer-reviewed research on photobiomodulation. It is not medical advice, not a treatment protocol, and not clinical guidance for any individual patient.
References to research describe what published studies reported. They are not claims about the ThyRed device or about any health outcome you should expect.
ThyRed is positioned as a wellness device. Not intended to diagnose, treat, cure, or prevent any disease.
This page is educational content intended for healthcare professionals and summarises third-party, peer-reviewed research on photobiomodulation. It does not constitute medical advice, a treatment protocol, or clinical guidance for any individual patient. Cited studies describe the findings of their respective authors and do not represent claims about the ThyRed device.
ThyRed is positioned as a wellness device. Not intended to diagnose, treat, cure, or prevent any disease. Clinical decisions remain the responsibility of the treating clinician.