You saw the ad for the cap with red diodes in it, or someone offered you a “laser hair session” at the end of your appointment, and the doubt stayed with you. Before spending money on it, it is worth changing the question. It is not whether laser works. It is which kind of hair loss it has been studied for, and at what dose.
Both answers change depending on what is actually thinning your hair. Most of the material you found online does not make that distinction, because nobody selling a device gains anything by separating the cases.
What the light does down there
The technical name is photobiomodulation. The most widely accepted hypothesis runs like this: red light (somewhere between 630 and 680 nanometres) and near-infrared light (around 800 to 830) pass through the skin and are absorbed by an enzyme in the mitochondria called cytochrome c oxidase. The mitochondrion is the structure that produces energy inside the cell, and that enzyme is the last step in the production line.
The absorption increases ATP output (ATP being the molecule the cell uses as energy) and alters local signalling. In the follicle, the effect that matters is pulling units out of rest and returning them to the growth phase, as well as making that phase last longer.
Notice what that sentence implies: there has to be a living follicle there to respond. Light does not create a follicle where one has already closed.
And there is a detail no advertisement mentions. The response is biphasic. Too little dose produces no effect; too much inhibits instead of stimulating. It is not a case of “the longer the better”, and that holds for both the length of the session and how often you use it.
The label every ad quotes
“FDA approved” appears on almost every page selling one of these caps. The FDA is the agency that regulates drugs and devices in the United States, and the correct word here is cleared, not approved. The route used is the 510(k), the equivalence pathway: the manufacturer shows that the device is substantially equivalent to another one already on the market, and that it is safe. That is not the same bar as a drug approval, which requires demonstrating efficacy.
Which is why there are dozens of cleared devices and very few with a published clinical trial of their own. Clearance says the thing probably will not hurt you. It does not say it works for your case.
Brazil has its own equivalent: devices sold here are meant to carry an Anvisa registration, Anvisa being the national health surveillance agency. Same logic applies. A registration number is a regulatory fact, not a result.
Where there is research, and where there is not
| Condition | What evidence exists for light | Note |
|---|---|---|
| Androgenetic alopecia (pattern hair loss), female and male | Controlled trials with a sham group, meaning an identical device switched off, generally 16 to 26 weeks, showing gains in density | This is where virtually all of the positive literature sits. A good share of it manufacturer-funded |
| Telogen effluvium (diffuse shedding with a datable trigger) | Almost nothing designed specifically for it | The condition resolves on its own in six to nine months, so anything used in the meantime looks as though it worked |
| Alopecia areata | Small studies, inconsistent results | An autoimmune disease, managed with a dermatologist |
| Scarring alopecias (lichen planopilaris, frontal fibrosing alopecia, folliculitis decalvans) | No evidence of regrowth | The follicle has been replaced by fibrosis. There is nothing left to stimulate, and active inflammation is a medical matter |
| Traction alopecia | Not the mechanism | The treatment is removing the traction. At a late stage the condition becomes scarring |
On the size of the effect in that first row, it is worth being specific: the positive trials report modest gains, measured over a small area, in the range of a few hairs to a few dozen hairs per square centimetre, across four to six months. For comparison, a scalp with good density carries somewhere between one and two hundred hairs per square centimetre.
That is a real gain and a small one. You will see it in the measurement before you see it in the mirror, and anyone promising otherwise is selling you something else.
Laser and LED are not the same thing
Laser is coherent light, concentrated into a very narrow band. An LED (light-emitting diode) is not coherent and covers a wider band. Most of the positive trials in hair loss used laser diodes; LED panels arrived later, with a thinner literature behind them.
What seems to decide the biological effect is the wavelength and the dose delivered to the skin, not coherence as such. But that is a reasonable inference, not an equivalence demonstrated device by device. A comb with eight diodes and a helmet with two hundred are not delivering the same thing, even when both have the word laser printed on the box.
Three questions separate a device from an ornament: what is the wavelength, how much power reaches each square centimetre of scalp, and how many minutes does a session last. If the answer is “it is imported technology”, there is no dose.
Casual use is the problem, not the device
In the studies, the usual pattern is three times a week, fifteen to thirty minutes, for four to six months, without skipping. The effect depends on continuity. When use stops, the gain tends to recede over the following cycles, because the cause is still sitting there. In androgenetic alopecia, no light has altered how sensitive the follicle is to the hormone.
That is the part that dismantles the idea of a miracle device. Light does not treat a cause. It improves the response of a follicle that still has the capacity to respond, and it improves it only a little when it is working alone.
Inside a protocol the conversation is different, because by then someone has established which kind of hair loss this is, whether ferritin, thyroid or a current medication is part of the picture, whether there is inflammation on the scalp, and what goes alongside it. The light becomes one item with a defined job, not the whole treatment.
When light is the wrong question
See a dermatologist first, rather than buying a device, if there is a patch with a sharply defined border; smooth, shiny scalp where you cannot see the small openings the hairs come out of (the ostia); a sore, crust, pus or pain; a new pigmented spot on the scalp; or hair loss alongside general symptoms.
It is also worth postponing light therapy while taking a photosensitising medication (isotretinoin, some tetracyclines, St John’s wort, among others), which changes how the skin responds. Any device with laser diodes calls for eye protection.
What to do with what you have just read
Before buying a cap or signing up for a package of sessions, two things. Know the name of your hair loss, not just that “it is falling out”. And ask what measurement they will be comparing against, and at which session: trichoscopy of the same area, at the same magnification, before and after.
With no defined cause and no measurement, light becomes an expensive three-times-a-week habit that nobody can evaluate.
If you would like to talk about your case
The assessment with a trichoscope (a camera that magnifies the scalp heavily) shows on the screen, with you following along, whether the hairs are miniaturising, whether the ostia are preserved and whether there is inflammation. You watch the trichoscopy together with the professional as the images come up; there is nothing handed over on paper. It is that assessment that decides whether light makes sense in your protocol, at what dose, and alongside what.
R$200 (Brazilian reais), credited in full towards the protocol. We measure again during or at the last session and compare with the image from the first day, at no extra cost.
Tuesday to Saturday, 9am to 6pm, by appointment, in Tatuapé, in the East Zone of São Paulo, near the Carrão and Tatuapé metro stations. Tuesday is the day reserved for scalp therapy. We offer service in English.