Migraine sufferers might want to stay out of the heat on warm days, as a new study suggests that hot weather can trigger headaches, the BBC reports. For every five-degree Celsius increase in temperature, the risk of developing a migraine or non-migraine headache rose by 7.5 per cent, according to a study of over 7,000 patients suffering from headache who visited a U.S. hospital’s emergency room over a seven-year period. Among the pool of patients, 2,250 were diagnosed with migraine, and 4,803 with “tension” or “unspecified” headaches. In the study, published in the journal Neurology, researchers looked at meteorological and pollutant monitors in the lead-up to the patient’s visit, and again in the days after. While temperature seemed to impact headache risk, air pollution had no effect.