Quick definition: Photobiomodulation (PBM) is the use of low-power red or near-infrared light, from lasers or LEDs, to influence how cells behave without heating or damaging tissue. The leading theory is that mitochondria absorb the light. It is the scientific name for what most people call red light therapy or low level light therapy.
What is photobiomodulation?
Photobiomodulation combines three ideas: photo (light), bio (living tissue), and modulation (a change in activity). Instead of cutting, heating, or resurfacing skin like ablative lasers, PBM uses gentle, non-thermal light doses meant to nudge cell activity.
Wikipedia's overview of low-level laser therapy describes it as a photochemical treatment that applies low-power lasers or light-emitting diodes to the body without damaging tissue. The same article notes the field has many names, including red light therapy, cold laser therapy, soft laser therapy, and photobiomodulation therapy, with the last now preferred.
From low level light therapy to PBM: why the name changed
For decades, researchers called this field low-level laser therapy (LLLT). As LEDs became common light sources, "laser" no longer fit, and the acronym was often read as low level light therapy. "Photobiomodulation therapy" has since become the preferred term because it describes the biological effect rather than the light source. Today you will see PBM, PBMT, LLLT, and red light therapy used for overlapping ideas in both research and marketing.
The field began by accident. Hungarian physician Endre Mester was trying to replicate an experiment suggesting ruby lasers could reduce tumors in mice, and instead noticed an effect on hair, which he published in 1967.
"low-level ruby laser light could regrow hair" — Wikipedia, Low-level laser therapy
That observation in mice helped launch decades of research on skin, hair, wound healing, and pain.
How photobiomodulation works
The most widely accepted explanation centers on the mitochondria. According to the generally accepted theory summarized on Wikipedia, the light-absorbing molecule is cytochrome c oxidase, a respiratory enzyme in the mitochondrial electron transport chain. When it absorbs red or near-infrared photons, cells may produce energy more efficiently and send signals that influence inflammation and repair.
Harvard Health puts it in plain terms: PBM is believed to stimulate mitochondria in ways that may reduce inflammation and support collagen, a structural protein that keeps skin strong and supple.
Several variables decide whether a PBM session does anything useful:
• Wavelength. Red and near-infrared light are used most because they reach deeper than blue or green light.
• Irradiance (power per area) and fluence (total energy per area). Too little light may do nothing; too much does not add benefit and can reduce it.
• Beam geometry. How light spreads from the source affects what actually reaches the skin.
• Frequency and duration. Most studies use repeated sessions over weeks or months.
What photobiomodulation research shows
Skin. In a controlled trial in Photomedicine and Laser Surgery, Wunsch and Matuschka gave 113 volunteers 30 sessions of red or red-to-near-infrared light and compared them with 23 controls. Treated groups showed improved skin complexion and feeling, reduced roughness, and higher collagen density measured by ultrasound.
Hair. A 2019 meta-analysis in Lasers in Medical Science by Liu and colleagues pooled 11 randomized, double-blinded trials of LLLT for androgenetic alopecia and found a significant increase in hair density compared with sham devices. Lower treatment frequency performed better than higher frequency.
Home-use devices. Output quality varies. A 2025 pilot study in Dentistry Journal by Cronshaw and colleagues measured five consumer PBM LED torches and found a wide range of wavelengths, output power, and irradiance, with some devices losing about half their initial output within three minutes.
"inconsistent with accurate dose delivery" — Cronshaw et al., Dentistry Journal
The takeaway: PBM is a real area of research with encouraging findings, but results depend heavily on the device and dose. Wikipedia's summary notes that its effectiveness is still under investigation.
Common misconceptions
• "It's the same as a tanning or UV lamp." No. PBM uses visible red and invisible near-infrared light, not ultraviolet.
• "It heats the skin to work." PBM is defined as non-thermal. Some devices add warmth for comfort, but warmth is not the mechanism.
• "More light is always better." Research repeatedly finds a dose window, beyond which extra light adds little or less.
• "All red light devices are equal." Measured output can differ widely from what is printed on the box.
Photobiomodulation in beauty and personal care
In aesthetics, PBM shows up as in-office LED beds and panels, LED face masks, handheld wands, and scalp devices such as combs, caps, and helmets. Dermatology offices may pair it with other treatments, while at-home devices focus on convenience and routine use. People commonly use PBM-style devices for smoother-looking skin, the look of fine lines, and scalp care. For the face-focused view, see our red light therapy for face entry.
How Reseen fits in
Reseen designs at-home devices that apply these light principles in a cosmetic routine using VIPE™ precision light. Glow pairs 660nm red, 460nm blue, and 1064nm near-infrared emitters in a facial wand for firmer-looking, more radiant skin. Weave (39 × 660nm red emitters) and Halo (coming soon; 128 red + 128 blue light points) are built for a healthier-looking scalp and fuller-looking hair. The research above describes study results, not claims about Reseen products.
Frequently asked questions
Is photobiomodulation the same as red light therapy?
Mostly, yes. Photobiomodulation is the scientific term, and red light therapy is the popular name. PBM also covers near-infrared light, which is invisible.
What is photobiomodulation therapy used for?
Researchers have studied it for skin appearance, hair density in pattern hair loss, wound healing, and pain. In beauty, it is used mainly for skin texture, fine lines, and scalp care.
Is low level light therapy safe?
Low-level light is non-thermal and contains no UV, and Harvard Health describes red light therapy as considered safe, with minimal side effects. Protect your eyes, and check with a dermatologist if you take photosensitizing medication or have a skin condition.
How long does photobiomodulation take to show results?
Studies typically run for weeks to months with repeated sessions. Consistency and correct dosing matter more than long individual sessions.
Browse every term in the Reseen glossary.
Sources
1. Low-level laser therapy (photobiomodulation) — Wikipedia
2. Red light therapy for skin care — Harvard Health Publishing, 2025
3. A controlled trial to determine the efficacy of red and near-infrared light treatment in patient satisfaction, reduction of fine lines, wrinkles, skin roughness, and intradermal collagen density increase — Wunsch A, Matuschka K. Photomedicine and Laser Surgery, 2014
4. Comparative effectiveness of low-level laser therapy for adult androgenic alopecia: a system review and meta-analysis of randomized controlled trials — Liu KH et al. Lasers in Medical Science, 2019
5. Photobiomodulation LED Devices for Home Use: Design, Function and Potential: A Pilot Study — Cronshaw M et al. Dentistry Journal, 2025
This article is for general education and is not medical advice. Reseen devices are cosmetic devices and are not intended to diagnose, treat, cure, or prevent any disease. If you have a skin or scalp condition, talk to a board-certified dermatologist.