Light sensitivity, or photophobia, is a common symptom of migraine. Anyone who’s suffered from the debilitating condition knows that taking refuge in a very dark room is a common way to attempt to control the pain, nausea, aura, muscle soreness, and other effects. So it may come as a surprise to learn that one hue of light — green — is at the cutting-edge of promising research on migraine relief.
Green light may not only trigger fewer migraines than other colors of light, but also reduce the severity and frequency of migraines over time.
See the light
Pain researchers from a variety of fields have been exploring the connection between light and pain for the past few years, both in animals and humans. Among them are anaesthesiologists. Though their stock-in-trade is using pharmaceuticals to reduce or eliminate pain in a variety of medical settings, they too are looking for drug-free, non-invasive treatment alternatives.
One of the first studies, published in 2016, looked at the mechanisms underlying photophobia, which occurs in a range of neurological and ophthalmological conditions. In a study of 69 people — all of whom had fewer than five headache-free days per month — the researchers from Harvard Medical School and other institutions exposed participants to pulses of white, blue, green, amber and red light.
Nearly 80% of participants felt more pain in response to every color except green, which actually reduced pain in 20% of them. Green light also improved their mood. The researchers theorized that the reaction may have been caused by the brain’s wiring, with light signals and pain signals getting crossed in a brain region called the thalamus.
As NPR reported, newer green-light studies led by University of Arizona anaesthesiologist Mohab Ibrahim are showing promising results too. In a 2018 study, participants spent two hours every day sitting in a room illuminated only by a green light. Over time, the intensity of their migraines reduced by 60%, and the number of migraines they experienced every month dropped from 20 to six.
There’s still a lot of research to be done on green-light therapy, including testing for exposure length, intensity, and environment. (Sitting in a green-illuminated room for two hours a day, for example, is unlikely to be a viable long-term solution for most people.) Moreover, the neural circuitry isn’t well understood. The therapy may prove to be less of a pain-eliminating panacea than a complementary therapy used in conjunction with others.
Still, the results have been intriguing enough that the National Institutes of Health has given the green light to several green-light studies in the form of funding. One study will investigate whether green light’s use as an analgesic might help quell the overuse of opioids, while Dr. Ibrahim received a $1.7 million grant to look into green light’s potential to treat chronic pain.
Jen Pinkowski is a science writer based in Berlin. Her work has appeared in National Geographic, Washington Post, The New York Times, Mental Floss, Atlas Obscura and Archaeology.