Does Red Light Therapy Work Through Clothes?

Partly, and less than most people expect. Some red and near-infrared light passes through fabric, but how much depends on the colour, the weave and the thickness: in laboratory measurements, white fabric let through roughly a third to two thirds of the light, while dark garments let through between nothing and 3% of visible light. Near-infrared gets through a little better than red because many clothing dyes absorb far less beyond the visible range. Since you cannot tell by eye what a given shirt passes, the reliable approach is to uncover the area you are treating. You do not need to be naked. This article gives the measured figures for fabric, towels, dressings, hair, fur and glass, and what to wear for a session at home or in a studio.

Does red light therapy work through clothes?

Some light gets through light, thin fabric and very little gets through dark or thick fabric. Bare skin is the only condition in which the full dose arrives.

Fabric is yarn with gaps between the threads. Light that meets a gap passes straight through, light that meets a fibre is scattered, and light that meets dye is absorbed. Textile researchers have measured the result across the same wavelengths that light devices use.

The 2021 study measured ordinary and reflective fabrics from 200 to 1,100 nm. Communications in Development and Assembling of Textile Products, 2021 The 2023 study tested cotton in three weaves and found that a tighter weave passed less. Polymers, 2023 The dermatology study measured 16 garments in cotton, polyester, polyamide, nylon and denim. Anais Brasileiros de Dermatologia, 2020 These were broadband laboratory measurements, so treat them as ranges. The last row of the table is the most useful: the same black polyester, without and with a finish you cannot see, passed very different amounts.

Does near-infrared light pass through clothing better than red?

Yes, somewhat, and the reason is the dye. Clothing dyes are made to absorb visible colours, and many of them absorb far less beyond about 700 nm.

The 2023 cotton study found that its dyes had "lesser absorption ability" in the near-infrared than in the visible range, and in the 2021 study white cotton passed 37% of visible light and 36 to 41% of near-infrared. So without dye the fibre treats the two much alike, and it is the dye that separates them. A 2025 study that viewed an 850 nm source through three layers of clothing (a wool knit, a shirt and a T-shirt) with an infrared camera reported that clothing reduced the intensity but was not a barrier to those long wavelengths. Scientific Reports, 2025

That is useful to know, with two limits. Even white and undyed fabrics passed less than half of the near-infrared in the measurements above. And red light, which does its work in the skin itself, is the part clothing takes most of. For a session aimed at skin, uncovering matters most.

How much does clothing reduce the dose?

By the same share that the fabric blocks. If a shirt passes 40% of the light, the skin under it receives 40% of the dose in the same minutes.

Dose is irradiance multiplied by time, the sum we set out in how much red light therapy is too much. As a worked example, our panel's published output of at least 1567 W/m² at 6 inches is about 157 mW/cm², which over 10 minutes comes to about 94 J/cm² on bare skin. Through a fabric that passes 40% the same session delivers about 38 J/cm². Through one that passes 10% it delivers about 9 J/cm². Layers multiply: two layers that each pass 40% together pass about 16%.

Running the session longer to make up the difference is not a good trade. You do not know the figure for your garment, red and near-infrared are cut by different amounts so the balance of the light changes, dark fabric warms as it absorbs, and the limits in the manual still apply. Rolling up a sleeve is easier.

Do you need to be naked for red light therapy?

No. You need the area you are treating to be uncovered, and the rest of you can stay dressed.

Studios that publish their rules follow the same principle. Those with private rooms ask for underwear or dry swimwear with as much skin exposed as is comfortable, and those with shared rooms ask for light gym clothing. At home it comes down to the target:

• Face: nothing to remove. Tie hair back off the forehead and cheeks, and start with clean skin, as covered in using a red light mask with make-up or sunscreen.
• Knee, elbow or shoulder: shorts or a rolled sleeve. Take off supports and sleeves for the session.
• Back or torso: shirt off, or a swimsuit that leaves the area clear.
• In a cold room: warm the room first and keep everything except the treated area covered.

Whatever you wear, put on the supplied goggles when you face a panel. Ordinary glasses do not do the job, since clear lenses let this light through.

Does red light work through a towel, socks, a compression sleeve or tape?

Poorly. These are thicker or denser than a shirt, so take them off for the session.

UK hospice guidance for light therapy asks patients to remove any compression garment over the area and applies the light directly to the skin or just above it. St Margaret's Hospice A bench study of 13 wound dressings found that the laser power transmitted "ranged between 98.6% and 0%, depending on the material and wavelength". Photomedicine and Laser Surgery, 2010 At the transparent end, thin clear plastic film cost only 0.8 to 2.3% of the light. Fisioterapia e Pesquisa, 2006

The pattern is that pigment and bulk block light, while a thin clear layer barely does. Those dressing studies come from clinical wound care. Our precautions say not to use either device on broken skin, so anything involving a wound or a dressing is a question for your clinician.

Does hair, a beard or fur block red light?

Yes, to a degree that depends on colour and density. Hair is pigment and fibre, the same two things that make cloth block light.

The clearest measurements come from veterinary research. In skin samples from 19 horses, laser light at 800 and 970 nm penetrated best through light-coloured hair and least through dark hair, and clipping the hair improved it. American Journal of Veterinary Research, 2016 Colorado State University's veterinary hospital advises that for dark-furred pets the hair is best shaved or, as an alternative, parted. Colorado State University

For people, that means keeping hair off the face under a mask and parting it where you can. For pets under a panel, part the coat over the area and check a dark coat for warmth, as described in red light therapy for dogs.

Does red light therapy work through glass or a window?

Through plain glass, mostly yes. Clear window glass passes about 89% of visible light, which includes red, and a somewhat smaller share of near-infrared.

The figure is for 6 mm clear float glass. Guardian Glass Modern energy-saving glazing is different: its thin metal coating is built to stay transparent to visible light while reflecting near-infrared. Lawrence Berkeley National Laboratory There is no reason to place a pane between you and a panel. The practical points are that a window is a privacy matter and not a light barrier, and that reading glasses are not eye protection.

What is the best way to set up a session?

Clean, dry, bare skin on the target area, at the distance in the manual, for the time in the manual. Cleveland Clinic's advice for LED sessions is the same starting point: a clean, make-up-free face and goggles on. Cleveland Clinic

For the 9-Spectrum Red Light Therapy Panel, that means 10 to 15 minutes per area, at 6 inches for a joint or 12 inches for a broad area, with the supplied goggles on and at least six hours between 30-minute sessions. Its nine wavelengths run from 480 to 1060 nm and each dims from 1 to 100% on its own. Keep towels and clothing off the panel housing while it runs. Hanging and positioning are covered in how to set up a red light panel at home. The 4-Wavelength Red Light Therapy Mask sits on the face, so clothing does not come into it: clean skin and hair tied back are all it needs.

Standard shipping to the US, UK and Germany is free. Read the precautions before ordering, since returns are accepted within 30 days, less a 10% restocking fee if the device is unopened with its seals intact, or 20% if it is opened but undamaged and complete.

Kivorla devices are general wellness devices, not medical devices. The fabric figures above are laboratory measurements of textiles under broadband light and are not tests of our devices through clothing. Do not use either device on broken skin, and speak to a doctor first if you have a skin condition.