Humans emit 'invisible' light that can help diagnose stress, injury: Study

For representation only. Image Source: Unsplash

Scientists have found that the ultraweak photon emission, or UPE — faint light naturally emitted by all living organisms — can act as a sensitive indicator of vitality in animals and stress response in plants. 

The study, published in The Journal of Physical Chemistry Letters by researchers at the University of Calgary, suggests that UPE imaging may soon become a powerful, non-invasive diagnostic tool.

UPE, also called biophoton emission, is the spontaneous release of extremely low-intensity light emitted by living systems. 

Unlike bioluminescence, which glows brightly and can be seen with the naked eye (like in fireflies), UPE is so faint it is invisible to humans. It spans the spectral range of 200 to 1,000 nanometers and is emitted by organisms ranging from bacteria and plants to animals and humans.

What makes UPE fascinating is that it doesn't require any external light source to trigger it. It is instead linked to internal biochemical activity.

One of the key players is reactive oxygen species (ROS), which are highly reactive molecules generated during cellular metabolism—the energy-producing processes within cells. 

When an organism is under stress—such as injury, extreme temperatures, or chemical exposure—ROS levels rise, these molecules can excite electrons, which then release photons (light) as they return to a lower energy state. This photon release is what is detected as UPE.

Despite its prevalence, UPE's relationship with stress and life status isn't yet fully understood. To probe this, the Calgary team devised a series of experiments comparing light emissions from living versus dead mice, as well as plants subjected to various stressors.

The researchers placed mice and plants in specially designed "ultra dark" chambers to block any ambient light. They used highly sensitive imaging equipment: an Electron-Multiplying Charge-Coupled Device (EMCCD) camera for plant samples, and a Charge-Coupled Device (CCD) camera integrated with an In Vivo Imaging System (IVIS) for mice. 

In mice, results were striking. Even though both live and euthanised mice had identical body temperatures (37°C), only the live animals emitted robust UPE. The recently deceased ones showed almost no emission.

In plants, when they were exposed to increased temperatures, physical injury, or chemical treatments, UPE levels also increased noticeably. 

Damaged areas of leaves glowed more brightly under the imaging system than untouched sections. In fact, changes in light emission occurred almost immediately when stressed or treated.

According to researchers, the implications of the findings are far-reaching. Because UPE responds in real time to physiological changes, it could be used for early detection of disease, assessing plant health, or monitoring recovery after injury. 

They argue that UPE imaging may become a valuable, non-invasive tool for clinical diagnostics, agricultural monitoring, and fundamental studies in biology.