All living organisms continuously emit an extremely weak light. This phenomenon, called ultraweak photon emission, or biophotons, remains invisible to the human eye. However, highly sensitive cameras can record these photons produced by cells.
This emission corresponds neither to body heat nor to a form of bioluminescence like that of fireflies. It mainly originates from chemical reactions related to metabolism. Mitochondria, which provide energy to cells, appear to play a central role.
A sensitive camera captures biophoton emissions from a mouse (alive, left; dead, right).
Credit: Lana Frankle/University of Calgary
During these reactions, molecules containing oxygen can reach an unstable energy state. When returning to a more stable state, they sometimes release a photon. The resulting light covers visible and near-infrared wavelengths, among others.
An experiment published in 2025 made it possible to photograph this faint glow in live mice. After their death, the signal almost completely disappeared. This comparison showed the direct link between light emission and biological activity.
Researchers also observe an increase in the signal when cells undergo stress. An injury, infection, or metabolic disturbance can boost the production of reactive molecules. This reaction then increases the number of photons emitted.
This property could provide a new tool for studying tissue health. Teams are already comparing emissions from healthy and cancerous cells. Some studies report measurable differences, but their medical use remains uncertain at this stage.
The main obstacle comes from the weakness of the signal. Measurements require near-total darkness and cooled detectors. The emitted photons can also be absorbed or scattered by the skin and surrounding tissues.
A more controversial hypothesis suggests that cells might use this light to communicate. Several experiments have detected effects between cells separated by transparent barriers. However, these results remain difficult to reproduce and do not always exclude other mechanisms.
This phenomenon could nonetheless become an indicator of metabolic activity or oxidative stress. It could be used to test drugs, monitor organs before transplantation, or assess the viability of seeds. These applications still require solid experimental validation.