Red and Blue Light: How LED Skin Therapy Works

For the first three weeks I did everything wrong.

I switched the red mode on in the evening, over serum and oil, for about five minutes, every other day, whenever I remembered. After twenty days I looked in the mirror, saw nothing, and very nearly put the module away in a drawer. What saved it was some dull reading: I finally worked out how long a fibroblast actually needs to build anything, and realised I had been assessing the result roughly the way you would inspect a harvest three days after sowing.

The second mistake surfaced at the same time. Light does not pass through a thick layer of oil. I had spent three weeks illuminating my own serum.

I lead with this because light therapy is a field where almost every failure comes down to two things: the wrong assessment window, and a barrier between the diode and the skin. The mechanism itself is fairly transparent, and there is nothing mystical in it.

What light therapy is, and why the skin has a "window"

Light is a stream of photons at a given wavelength, and the wavelength decides everything. Hard ultraviolet ionises molecules and damages DNA. The infrared range mostly turns into heat. Between them lies a narrow band where light behaves differently: it is absorbed by specific molecules and changes their state without destroying the cell.

That effect is called photobiomodulation. The operative word is modulation — light does not deliver a substance into the tissue or remove one. It acts as a signal. A receiving molecule absorbs a photon, moves into an excited state, and ordinary biochemistry takes over from there.

Skin has what is known as an optical window, roughly 600 to 1200 nanometres. Below 600 nm light is strongly absorbed by haemoglobin and melanin; above 1200 nm, by water. Inside the window, radiation travels deepest. Red at 660 nanometres sits right at its start and reaches the dermis — the layer where fibroblasts live and the collagen scaffold sits.

The blue range, 415–430 nanometres, falls outside that window entirely. It is absorbed almost immediately and works at the surface: the epidermis and the openings of hair follicles, where the sebaceous glands sit. That is not a shortcoming but a division of labour. Two wavelengths, two targets, two depths.

In the Wentun device the LED module is one of three working components, alongside far infrared radiation at 8–14 μm and thermal stimulation of the meridians. The red and blue modes are switched on separately, and below I explain why that is the case rather than both at once.

How it works: two targets at two depths

The red range: mitochondria, ATP and the fibroblast.

Let me start with the energy side, because nothing further makes sense without it.

Almost every cell contains mitochondria — organelles that convert nutrients into the universal energy currency, ATP. Adenosine triphosphate pays for everything: division, contraction, transport, protein synthesis. Mitochondria produce it; the cell spends it.

In the mitochondrial respiratory chain there is an enzyme called cytochrome c oxidase — the final complex, passing electrons to oxygen. It is considered the primary chromophore for the red and near-infrared range: its copper centres absorb photons in that band. Absorption shifts the enzyme's state, electron transport picks up, and ATP synthesis rises.

Then the skin enters the picture. Fibroblasts live in the dermis and act as its builders. Their job is to synthesise extracellular matrix proteins: collagen types I and III, elastin, and the water-binding components including hyaluronic acid. It helps to picture the collagen scaffold as the spring unit of a mattress — while the springs are elastic the surface holds its shape; as they thin out, it starts to sag.

Collagen synthesis is expensive. A single molecule goes through triple-helix assembly, hydroxylation of proline and lysine, secretion, and extracellular cross-linking. All of it is paid for in ATP. A fibroblast with sluggish mitochondria does not build less out of spite — it simply cannot afford to.

Hence the logic of the red mode: more available energy, more fibroblast activity. In parallel, the red range influences microcirculation — capillary blood flow increases, the tissue receives more oxygen and substrate, and this shows up before anything else does, as evenness of tone.

This is also where my first mistake lived. Collagen turnover is a matter of months, not weeks. A sensible assessment window for the red mode is eight to twelve weeks of regular use. Anything visible in the first few days is microcirculation, not scaffolding.

The blue range: porphyrins and selectivity.

The blue story is a different one, and rather more elegant.

Billions of bacteria live on the skin and most of them are simply the normal microbiome. Among them is Cutibacterium acnes — called Propionibacterium acnes until 2016, and the old name still turns up in the literature. It lives in the follicular opening and feeds on components of sebum. While the balance holds it is harmless. When the sebaceous glands produce a surplus of sebum, it gains a nearly unlimited resource, the population grows, and the products of its metabolism trigger an inflammatory response.

The vulnerability of this bacterium lies in its own biochemistry. During metabolism it synthesises porphyrins, principally coproporphyrin III and protoporphyrin IX. These are photosensitive molecules with a pronounced absorption peak around 415 nanometres — the Soret band.

What follows is ordinary photochemistry. The porphyrin absorbs a blue photon, moves into an excited state and transfers energy to molecular oxygen. Singlet oxygen and other reactive oxygen species are formed — short-lived, aggressive particles that damage the bacterial membrane exactly where they arose.

The key detail is selectivity. Our own cells do not accumulate porphyrins in comparable quantities, so the reaction runs predominantly where the bacterium lives. The action radius of singlet oxygen is measured in tens of nanometres; it does not travel across the skin.

There is a second line as well: the blue range is described as affecting sebaceous gland activity, reducing excess sebum output. The distinction matters — this concerns surplus oil, not water. The skin is not dried out by it, and equally there is no miracle mattifying after a single session.

And the main question — why in sequence rather than together.

Here the engineering follows the physiology.

The blue mode is, in essence, a controlled local oxidative stress at the surface. The red mode activates cellular respiration and blood flow at depth. Mixing them in one session makes little sense for at least two reasons: the ranges have different targets at different depths, and it is reasonable to put the surface in order first and only then intensify the metabolic processes within it.

Hence the working sequence: blue first for clearing, red second for recovery. Not the other way round, and not simultaneously.

What it delivers — and what not to expect

The realistic list is short.

Density and tone. Not a "lift", but gradual firming through fibroblast work. The horizon is two to three months, and what usually changes first is surface quality rather than contour.

Evenness of tone. The fastest effect, because it rests on microcirculation rather than protein synthesis. It appears earlier than everything else and disappears earlier too if you stop.

The condition of blemish-prone skin. With regular use the blue mode supports control over excess oiliness and inflammatory lesions. It works through the mechanism described above, and it does not work on every form: nodular and cystic lesions are not a blue-light question, they are a dermatologist's.

The barrier. Indirectly: the less low-grade inflammation there is and the better matrix synthesis runs, the more stably the skin holds water.

Now for what not to expect. Light therapy does not replace prescribed treatment, systemic or topical. It does not work through clothing, make-up or heavy textures. It produces no "weekend" effect: any promise of results in a week belongs to marketing rather than to fibroblast biology. And it does not compensate for sleepless nights.

Who it suits — and who should skip it

A few clear groups gain most.

People past thirty-five, where a loss of skin density is already visible but aesthetic procedures feel early or unwanted. Anyone who lives through six months of heating season a year. People with oily and combination skin prone to inflammatory lesions — provided the forms are mild to moderate. Anyone whose face turns dull by the end of winter. And, separately, those who already use the device for far infrared and thermal work on the meridians but never touch the LED module, simply because they never worked out what it was for.

Now the honest part.

Photosensitisation is the main item. A number of medicines increase the skin's sensitivity to light: tetracyclines including doxycycline, retinoids including isotretinoin, some diuretics and antidepressants, St John's wort, certain topical preparations. If you take any of these, light therapy is discussed with your doctor before you start, not after the first reaction.

Eyes. There is no need to look at the diodes, particularly the blue ones: the retina is sensitive to short-wavelength blue light. Eyes closed, and protective goggles when working on the face.

Pigmented lesions. Any mole that has changed in size, colour or shape is not a place to experiment with light — it is a reason to see a dermatologist. Diagnosed melanoma and suspicious lesions are a contraindication.

Photosensitive forms of epilepsy, active skin conditions in a flare, fresh post-surgical wounds, and pregnancy: in all of these, a doctor comes first.

And the general frame I repeat in every article about devices. Home light therapy runs at domestic power levels and warrants domestic expectations. With regular use it supports the condition of the skin, and it is not a medical procedure.

How to use it: a practical protocol

Preparation first, because that is where most people come unstuck.

Skin must be clean and dry. No cosmetics, foundation, heavy oils or creams under the light — they scatter and absorb the radiation, and you will spend three weeks illuminating your serum, as I did. Skincare goes on after the session, not before.

Distance follows the device instructions. Too far and the dose falls off with the square of the distance; too close and coverage becomes uneven.

Order within a single session, if you use both modes: blue first, then red. Clearing, then recovery.

Duration and frequency. A starting point for home devices is on the order of ten to twenty minutes per zone, three to five times a week. "More is better" does not apply here: photobiomodulation is described as having a biphasic dose response, where past a certain threshold additional exposure stops adding benefit. Hour-long daily sessions do not speed anything up.

The assessment window. For the blue mode, first changes in inflammatory lesions are usually discussed within four weeks. For red, eight to twelve. Looking in the mirror and drawing conclusions before that is pointless.

How to assess it sensibly. A photograph every two weeks, in the same spot, under the same light, without make-up, from the same distance. A mirror is a poor measuring instrument: it reflects today's mood as much as today's skin. I only started seeing a difference once I began shooting by the same window at the same hour.

And the rule that applies to everything I write about: change one variable at a time. If you started a new serum, switched cleanser and moved your bedtime an hour earlier alongside the light, you will never know what worked.

One word on where the LED module sits within the Wentun device. It does not replace the other two components and does not compete with them: far infrared radiation and thermal work on the points solve their own problems. LED is a separate tool with a separate target, and it makes sense to schedule it as its own block rather than as "an extra function that came in the box".

Conclusion

Light therapy is that rare case where the mechanism is understood down to the molecule, and a lack of results is almost always explained by discipline rather than physics.

Red light is absorbed by cytochrome c oxidase, raises ATP availability and gives the fibroblast the resource to synthesise collagen — that is months, not days. Blue is absorbed by bacterial porphyrins, and the reaction runs selectively where those porphyrins are — that is weeks. Surface first, depth second. Clean dry skin, a sensible dose, a photograph instead of a mirror.

My own conclusion, once I stopped doing everything wrong: the scarce resource here is not device power but patience. Eight weeks feels like a long time right up until you remember how many decades went into the previous version of your skin.