According to a new discovery published in the journal Science Translational Medicine, green light has the potential to become a simple, safe, and cost-effective method for pain relief in humans.
Previous studies have shown that green light—especially light from LED sources—can reduce pain levels in individuals suffering from conditions such as arthritis, migraines, and fibromyalgia. However, the underlying mechanisms of this effect have not been clearly understood. Recently, a research team led by neuroscientist Yu-Long Tang from Fudan University (China) has sought to unravel this mystery by studying the visual processing system, which includes the reception and processing of light, in mice.
Photoreceptor cells, including cones and rods, contributed to the pain-relieving effects of green light.
The researchers began their study by examining the rod and cone photoreceptor cells located at the outer layer of the retina and the intrinsically photosensitive retinal ganglion cells (ipRGCs, which receive signals) found in the inner retina. By selectively disabling each type of cell at different times and then assessing how they affected the pain perception in mice, the researchers discovered that the pain-relief mechanism starts from these photoreceptor cells. In other words, the eye cells and the neural pathways to the brain (responsible for pain relief) can be activated after exposure to low-intensity green light.
Specifically, through a series of experiments, the experts found that the cone and rod photoreceptor cells contributed to the pain-relieving effects of green light in both healthy mice and those with arthritis. “We found that cone photoreceptor cells in the retina are essential for pain relief through green light, while rod cells play a secondary role,” the authors explained. Following these findings, the research team continued to investigate the signaling pathways from the eyes to the brain. They discovered that when immersed in green light, the cone and rod cells stimulate a group of cells in the brain that help modulate and reduce the neural connections associated with intense pain, thereby effectively alleviating pain.
Previously, some animal studies had identified other mechanisms related to the pain-relieving effects of green light. However, this research marks a significant advancement by successfully identifying the pain sensation pathways in the brain of a mammal, thereby expanding the scientific community’s understanding of a potentially safe and easy solution for pain relief. Although it is not clear whether the perception of color between humans and rodents is the same, experts believe that the mechanisms of light reception and processing between the two species may be similar.
Regarding the efficacy of green light therapy, a study on mice indicated that the pain-relief effects following treatment with green light were sustained for up to four days. Recent clinical trials have also shown that a few hours of daily green light therapy help reduce pain intensity in a group of fibromyalgia patients and decrease the number of headache days in individuals suffering from migraines. Green light is also believed to benefit post-surgical patients by reducing their reliance on pain medications.
While green light therapy may not be effective for everyone, if its efficacy is validated in a larger patient population, it has the potential to become a safe alternative to traditional pain relief medications.
