Red light therapy through clothes is possible, but bare skin gives the most reliable dose. A 2025 optical study found that 850-nanometer near-infrared light was more visible through clothing layers than visible light, but that does not show that treatment through those clothes produces the same clinical result.
Red Light Therapy Through Clothes: At a Glance
| Clothing condition | Expected result |
|---|---|
| Bare skin | Most consistent dose |
| Thin, loose, light-colored T-shirt | Some light may reach the skin, especially near-infrared light |
| Dark cotton or synthetic fabric | More light absorption and less transmission |
| Denim, fleece, sweatshirt or multiple layers | Likely to block or substantially weaken the treatment |
| Wearable designed for use over clothing | Follow the manufacturer's instructions |
Why Does Clothing Reduce Red Light Therapy Effectiveness?
Clothing sits between the device and your skin. The fabric can absorb, reflect and scatter some of the light. It can also create uneven exposure across the treatment area.
Red light therapy, also called photobiomodulation, commonly uses visible red light from about 600 to 700 nanometers and near-infrared light from about 780 to 950 nanometers. Red light is generally used for more superficial targets. Near-infrared light can travel farther into tissue.
The amount of light that reaches your skin depends on the fabric's:
- Color
- Thickness
- Weave
- Material
- Number of layers
Light passing visibly through a shirt does not prove that the skin is receiving the same dose as it would with the shirt removed.
Does Near-Infrared Light Work Through Clothes Better Than Red Light?
Usually, yes. Near-infrared light tends to pass through ordinary fabric more readily than visible red light, but the result depends on the material, color, thickness, weave and number of layers.
The 2025 Scientific Reports study used an 850-nanometer near-infrared source and found that it was substantially more visible through several clothing layers than a visible-light source. The study was an optical demonstration, not a clinical trial showing that red light therapy works equally well through clothing.
A separate 2025 study tested 850-nanometer light through black cotton and biological tissue. The clothing reduced the transmitted optical power. Because the study used an ex vivo tissue and energy-transfer setup, it should not be treated as a direct clinical measurement of treatment effectiveness. It does show that clothing can reduce the amount of light reaching the target.
What Should You Wear During Red Light Therapy?
Expose the target area directly to the device whenever possible.
If you need to remain clothed, use:
- One thin layer of light-colored fabric
- Loose or loosely woven material
- No heavy layer over the treatment area
- The same clothing setup during each session
Avoid using red light therapy through denim, fleece, heavy cotton, dark sweatshirts, towels or several layers of clothing. These materials are more likely to reduce and unevenly distribute the light before it reaches your skin.
Check the device instructions as well. Some light-based procedures are performed while the patient is dressed, but FDA guidance for non-invasive body-contouring devices notes that clothing lowers the dose reaching the skin.
Is Clothing Acceptable for Different Treatment Goals?
Skin Concerns
Use red light on bare skin whenever possible. Skin-focused treatments rely on light reaching the surface layers directly, and visible red light is more easily reduced by fabric than near-infrared light.
Muscles, Joints or Deeper Tissue
Near-infrared light may pass through a thin shirt, but the delivered dose becomes harder to estimate. Bare skin is the better option when treating a knee, shoulder, back or another specific area.
Large Red Light Panels
Remove clothing from the treatment area if practical. This prevents the fabric from creating uneven exposure and keeps the setup more consistent from one session to the next.
Does Feeling Warmth Through Clothes Mean the Treatment Is Working?
No. Warmth does not prove that enough therapeutic light is reaching your skin. Fabric can absorb some light and convert part of that energy into heat. Photobiomodulation depends on the right wavelength and dose reaching the target tissue, not on how warm the area feels.
What Safety Precautions Apply?
Follow the device instructions for treatment distance, session length and eye protection.
The FDA advises caution for people with photosensitivity disorders, those taking photosensitizing medicines, people with active implants, and anyone with cancer, an active infection or an open wound at the treatment site. The FDA also advises caution during pregnancy.
Bottom Line
Expose the treatment area if you can. A thin, light-colored garment may allow some near-infrared light through, but clothing makes the delivered dose less predictable. Use a device over clothing only when the manufacturer specifically allows it.