Red light and your cells: what the science says is going on

That's a model, not a measurement in people, and depth alone doesn't tell you whether anything useful happens when the light gets there. But it's why near-infrared is often described as reaching further than red.

What the light is thought to hit: cytochrome c oxidase

Inside most of your cells are mitochondria, often described as the cell's power stations. They make ATP, the molecule cells use as an energy currency.

The leading theory is that the main target for red and near-infrared light is an enzyme in the mitochondria called cytochrome c oxidase. It's the last step in the chain that mitochondria use to make ATP. Karu (2010), one of the early researchers in the field, set out the case for this enzyme as the light's main receiver in a review. De Freitas and Hamblin (2016) describe it as one of the most important light-absorbing molecules in this research, partly because it contains metal centres that absorb light into the near-infrared range.

The nitric oxide hypothesis

Why would absorbing light make a difference? The most cited explanation involves nitric oxide.

The idea, described by de Freitas and Hamblin (2016) and again by Hamblin (2018), goes like this. In stressed cells, nitric oxide can bind to cytochrome c oxidase and slow it down. Light may knock that nitric oxide loose. With the brake off, the chain runs more freely, the charge across the mitochondrial membrane rises, and the cell makes more ATP.

The reviews also describe knock-on signals: brief changes in reactive oxygen species, calcium and other messengers that switch genes on or off. A second theory involves light-sensitive ion channels in the cell membrane that let calcium in.

Hamblin (2018) adds an important twist. Healthy cells and stressed cells can respond in apparently opposite ways to the same light. That matters, because a lot of lab work uses cells that have been deliberately stressed.

What the experiments actually showed

The mechanism isn't just a theory on paper. A few lab studies have measured it directly.

Back in 1984, Passarella and colleagues shone a helium-neon laser, which gives off red light, on mitochondria taken from rat livers. They reported a rise in the membrane charge and in ATP production. That's isolated mitochondria in a test tube, not a living person.

Ferraresi and colleagues (2015) used mouse muscle cells grown in a dish. After a single 90-second dose of combined red and near-infrared LED light, both mitochondrial membrane potential and ATP were higher than in untreated cells, with the biggest difference 3 to 6 hours later. Again, that's cells, not people.

In humans, the direct evidence is thin. Wang and colleagues (2017) shone a 1064 nm laser on the foreheads of 11 healthy volunteers and used a light-based scanner to track changes underneath. Compared with placebo, they saw more of the oxidised form of cytochrome c oxidase in the brain tissue they measured. It's an interesting signal, but it's 11 people, a laser at a longer wavelength than most home devices, and a measurement of a chemical change rather than any effect you'd notice.

Not everyone agrees

It would be misleading to present this as settled. Sommer (2019) argued that cytochrome c oxidase is not the main target for near-infrared light at all, and that water bound to the mitochondria plays the bigger role. That's a minority position in the papers we read, but it's a reminder that the field's best explanation is still a hypothesis.

Dose: irradiance multiplied by time

This is the part most product pages skip, and it's the part that matters most.

Irradiance is how much light power lands on each square centimetre, usually given in milliwatts per square centimetre (mW/cm²).

Time is how long that light stays on the same area, in seconds.

Multiply the two and you get the dose, also called fluence or energy density, in joules per square centimetre (J/cm²). In the Ferraresi cell study, 28 mW/cm² for 90 seconds gave about 2.5 J/cm².

Jenkins and Carroll (2011) set out what researchers should report so that anyone can repeat a study: wavelength, power, beam area, irradiance, time and the resulting dose, among others. When a paper or a product leaves those out, it's very hard to know what was actually delivered. Our guide to reading device specifications goes through what to look for.

Why more isn't better: the biphasic response

You might expect that if a little light helps a cell, a lot would help more. The lab research says otherwise.

Huang and colleagues (2009) described a biphasic dose response, where low doses stimulated cells and higher doses had less effect or the opposite effect. Their 2011 update reported the same pattern in ATP and mitochondrial membrane potential in cell studies, and in mouse experiments where both the dose per session and the number of sessions were varied.

A clear example comes from skin cells. Mamalis and Jagdeo (2018) gave human skin fibroblasts, the cells that make collagen, very high doses of red LED light: 320 and 640 J/cm². At those levels, a key growth signal fell, and the authors noted their earlier work showing that such high doses reduced fibroblast growth and collagen production. Compare that with the 2.5 J/cm² in the Ferraresi study. The same colour of light, at a very different dose, pushed cells in a different direction.

That's why "more power" or "longer sessions" isn't a sensible goal on its own, and why device instructions matter.

Where to go next

Each of these pages looks at one area of research and grades how strong the evidence is.

• Red light for muscle recovery: exercise performance and soreness trials, including whole-body studies that found little.
• Red light and collagen: what skin studies measured, from cell dishes to faces.
• Red light, energy and mitochondria: the evidence behind the "cellular energy" idea, most of it from cells and animals.
• Red light and sleep: a small, mixed set of studies.
• Red light and mood: early transcranial research, with a lot of caveats.
• The future of recovery and red light: what's still unknown and which trials are coming.

Who should check with a doctor first

Talk to your GP or pharmacist before using any red light device if you're pregnant, take medicine that makes your skin sensitive to light, have an eye condition, or have epilepsy that's triggered by flashing or flickering light. Read our pages on eye safety and side effects before you start.

What this means and doesn't mean

Here's the honest summary. There's a reasonable, lab-backed theory for how red and near-infrared light could change what a cell does. It centres on mitochondria and cytochrome c oxidase. The effect depends heavily on dose, and too much can work against you. Most of the direct mechanism evidence comes from cells and animals, and some scientists dispute the main target.

What this doesn't do is prove that any home device produces a benefit you'd notice. That's a question for human trials, which are covered topic by topic in the pages above.

The future of recovery: where red light research goes next

Why red light is a growing area of recovery research, what is still unknown about dose, devices and blinding, and which better-designed trials are under way.