A decade-long study of 7,032 people found associations between pollution, UV exposure and migraine visits; it did not show these factors cause attacks.
Air pollution, strong sunlight and certain weather conditions may be linked to more migraine-related healthcare visits. A decade-long observational study of 7,032 people in Israel found that short-term exposure to higher levels of nitrogen dioxide was associated with more visits for migraine. The findings add environmental conditions to the factors people may track, but they don’t establish that those conditions cause attacks.
Published in Neurology, the research examined daily pollution levels and weather, then compared them with hospital and clinic visits for migraine. Researchers considered conditions on the day of each visit and during the preceding seven days. They also reviewed triptan purchases, which can indicate use of fast-acting prescription medicines intended to stop a migraine.
What the study found
During the study period, 2,215 participants—32% of the group—had at least one hospital or clinic visit for migraine. Triptans were purchased by 47% of participants at some point, and most of those purchasers used at least two tablets a month.
The researchers found associations with three environmental factors: air pollution, temperature and UV exposure, and humidity. People exposed to high levels of nitrogen dioxide, a pollutant commonly produced by traffic exhaust, were 41% more likely to visit a hospital or clinic for migraine than those without high exposure. The days with the most visits also had higher pollution levels; the day with the fewest visits had lower-than-average pollution.
High UV exposure was associated with a 23% greater likelihood of a healthcare visit for migraine symptoms. High temperatures and low humidity also appeared related to more headaches, possibly by amplifying the effects of nitrogen dioxide. The study did not report that every person exposed to these conditions developed symptoms, and its findings concern healthcare visits and medication purchases rather than a direct count of all migraine attacks.
As hot weather and pollution can coincide in late spring and summer, the results may be useful context for people who already notice a connection between their symptoms and environmental conditions. The researchers also pointed to increasingly frequent heat waves and pollution as reasons to pay attention to these possible links. The study itself, however, cannot show how future weather patterns might affect migraine for any particular person.
Why these conditions might matter
The research found links, not proof of cause. Still, clinicians say there are plausible ways pollution and heat could affect the nervous system. Sana Ghafoor, MD, a neurologist at Tufts Medical Center, describes air pollution as a possible source of neuroinflammation, an inflammatory response involving the brain and spinal cord. That response may prompt the release of pain-related chemicals such as calcitonin gene-related peptide (CGRP) and substance P, which are associated with migraine.
Pollution may be especially relevant for some people with allergies, says Clifford Segil, DO, a neurologist at Providence Saint John’s Health Center in Santa Monica, California. If the body reacts to polluted air as it would to an allergen, that immune response could help set off symptoms in someone sensitive to this trigger. This is a possible explanation, not a mechanism proven by the study.
Heat may affect blood vessels and nerves, Segil says. Warming can change the diameter of blood vessels and nerves in confined areas, potentially irritating them. Hot conditions can also increase the chance of dehydration, which Ghafoor identifies as another possible migraine trigger.
Humidity may matter in its own right. Sweating in humid conditions can lead to water loss; if fluids aren’t replaced, blood volume may fall, according to Segil. Ghafoor also says she sees more patients with migraine when humidity is high, and that even modest changes in atmospheric pressure may affect nerve endings and sinuses. These explanations help make the findings plausible, but they don’t confirm that heat, humidity or pollution will trigger symptoms in every person.
Environmental factors are only part of the picture
Migraine triggers differ from person to person. Commonly reported factors include stress and anxiety; hormonal changes; bright or flashing lights; loud sounds and strong smells; some medicines; changes in sleep, weather or surroundings; intense physical activity; tobacco; caffeine or caffeine withdrawal; missed meals; and medication overuse.
Some people also report food-related triggers, including alcohol, chocolate, aged cheese, MSG, certain fruits and nuts, fermented or pickled foods, yeast, and cured or processed meats. A trigger list can offer a starting point, but it doesn’t mean everyone with migraine needs to avoid every item. A headache diary may help reveal patterns over time, Ghafoor says.
Practical steps and when to seek advice
Pollution, heat and humidity can be difficult to control, but noticing when symptoms occur may help someone discuss patterns with a clinician. For people who want to limit exposure to polluted air, Segil suggests a face mask such as an N95 outdoors. Keeping windows closed and using an air purifier may reduce indoor pollution, while checking pollution levels may help someone choose when to spend time outside, Ghafoor says.
During hot, humid weather, Ghafoor recommends paying attention to hydration, including electrolytes as well as water. Anyone unsure what approach is suitable for them, or concerned about recurring headaches, can discuss symptoms and possible triggers with a doctor or pharmacist. A clinician can also help review medicines, since the study included prescription triptans and medication use among the information researchers considered.
The useful takeaway is to treat these environmental links as clues to observe, not a forecast of when a migraine will happen. Tracking personal patterns and discussing them with a healthcare professional can help put the study’s population-level findings into context.
