Did you know that you are emitting light right now? It’s not a metaphor, nor new-age poetry, but a real biological phenomenon. This glow, incredibly faint, escapes the naked eye, but it is indeed present: emitted by your cells, it varies over the course of the day, responds to stress… and could even disappear at the moment of death. A fascinating discovery, which literally lights up our understanding of living beings.
An invisible light, but very real
This phenomenon is called Ultraweak Photon Emission (UPE). It was detected for the first time in humans in 2009 thanks to extremely sensitive cameras. Researchers observed, in total darkness, volunteers who were sleeping — and found that their skin produced a faint shimmer.
Nothing to do with the spectacular bioluminescence of fireflies or jellyfish: here, the light is a thousand times too weak to be perceived by the human eye. It does not depend on an enzyme like luciferase, but on a chemical process linked to our cellular metabolism.
The origin of this glow
This luminescence comes from the mitochondria, the energy hubs of our cells. When they produce ATP (the energy molecule), they also generate reactive oxygen species (ROS). These ROS react with other cellular components, such as lipids or natural pigments, producing a minuscule emission of photons.
This process follows a circadian rhythm: our body’s glow fluctuates over the hours. On average, the face is slightly brighter than other parts of the body.
A revealing light
But this glow is not merely a byproduct of our biology. Recent studies conducted on plants and mice show that it can also vary in response to stress or physiological changes.
In a plant, for example, the glow increases after pruning, signaling the onset of a healing process. The same occurs after applying an anesthetic such as benzocaine. This suggests that one day this luminous signature could serve as a tool for monitoring plant health, detecting perturbations long before they become visible.
In mice, researchers documented a dramatic drop in light emission after death, suggesting an immediate metabolic extinction. A striking, almost poetic image: at the moment life ends, the light also fades.
A boundary between life and death?
This observation raises a troubling hypothesis: what if, literally, we extinguish at the moment of our death? If this light, imperceptible, is a direct marker of our biological vitality?
In humans, this remains to be confirmed, but data from animal models open a promising route to study the last moments of life at the cellular level.
An emerging field of study
Better understanding UPE could lead to concrete applications: in medicine, to detect cellular imbalances early, or in ecology, to discreetly monitor the health of plants and ecosystems. What was previously regarded as a mere biological curiosity could well become a valuable tool for deciphering life itself.
The study is published in The Journal of Physical Chemistry Letters.
