Photobiomodulation

Photobiomodulation (PBM) is therapy using red and near-infrared light (typically ~630–850 nm; the studies below use 670 nm). The long wavelengths penetrate tissue and are absorbed by cytochrome c oxidase in mitochondria. The proposed mechanism: red light reactivates cytochrome c oxidase molecules that nitric oxide has switched off, raising ATP production and antioxidant-enzyme levels, which both fuels cellular repair and mops up reactive oxygen species (ROS). Since ageing mitochondria leak more ROS and make less ATP, PBM is pitched as a way to "adjust the ageing mechanism" (Glen Jeffery, UCL Institute of Ophthalmology).

Evidence, by tier

Established clinical use

• Oral mucositis from radiation/chemotherapy: red LEDs in the mouth improve symptoms in more than half of patients.
• Ophthalmology and dermatology already use red light for age-related decline in eyes and skin (see Skin Ageing and Retinoids).

Small human studies

• Retina, 2020 pilot (Jeffery et al., Journals of Gerontology A, doi 10.1093/gerona/glaa155): 24 adults, 670 nm torch for 3 min/day for 2 weeks; colour-contrast sensitivity improved ~20% on average in those over 40, no effect under 40.
• Blood glucose, 2024 RCT (Powner & Jeffery, Journal of Biophotonics): 30 healthy non-diabetic adults, 15 min of 670 nm light on the back vs sham; peak glucose after a sugary drink 7.5% lower, integrated 2-hour rise 27.7% lower. Authors flag that a warming/blood-flow explanation is not excluded.

Preclinical / speculative

• Brain and spinal-cord injury: University of Birmingham implantable silicone LED device (Davies), ≥20% less cell death in culture and rodents; pig trials next, no human data.
• Parkinson's, Alzheimer's, anxiety, depression, ADHD, PTSD: "early-stage research".
• Physiotherapy and post-operative pain: claimed, no studies cited.

The dosage problem

Outcome depends on source distance, wavelength, device power and exposure length — and more is not better: overexposure causes a metabolic "traffic jam" and ATP output falls. Most consumer products (masks, blankets, infrared saunas) ignore dose, and much supporting research is small, poorly controlled and commercially coloured. Jeffery's baseline: roughly 20 minutes outdoors several times a day gives a healthy person all the red light the biology needs.

Open questions

• Whether the glucose effect is metabolic or thermal, and whether it appears in people with diabetes (cf. Type 2 Diabetes Remission — unrelated evidence base, different population).
• Dose-response curves for any indication beyond mucositis.
• Whether the "modern light environment" hypothesis (windows block infrared, LEDs over-supply blue) has measurable health effects.

Related

• The Surprising Benefits of Red Light (Economist) — source article (2026-07-25).
• Skin Ageing and Retinoids — shares the pattern of a thin evidence core surrounded by a large wellness market.