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An international team led by researchers from Monash University have found that cooling patients’ brains after traumatic head injury does not improve outcomes, compared with patients who did not undergo brain cooling. The benefits of brain cooling in the intensive care unit after a traumatic brain injury have long been contentious. The rationale is that cooling, or hypothermia, reduces brain inflammation and consequently brain damage. Many laboratory studies have supported this hypothesis, and most clinical studies and the traumatic brain injury guidelines have found benefits for patients. However, many doctors remain skeptical about cooling because most clinical studies have not been of high quality, the better studies had limitations, and hypothermia requires expensive equipment and has known complications. The Prophylactic Hypothermia Trial to Lessen Traumatic Brain Injury (POLAR) was a multicentre randomised trial that included 511 patients with traumatic brain injury in six countries — France, Switzerland, Qatar, Saudi Arabia, Australia and New Zealand — and found that the proportion of patients with favourable neurological outcomes 6 months after brain trauma was the same whether patients had undergone cooling or not (cooling, 48.8%; normal temperature, 49.1%). Favourable neurological outcome was defined as a Glasgow Outcome Scale – Extended (GOS-E) score of 5–8 (a GOS-E score of 1 indicates death, 2 indicates vegetative state, 3–4 indicates severe disability, 5–6 indicates moderate disability, and 7–8 indicates good recovery). Mortality at 6 months was 21.4% for patients with hypothermia, and 18.4% for those with a normal temperature target. Findings were similar after adjusting the analysis for the severity of the injury and for the analysis of specific patient subgroups. The POLAR trial was presented at the annual meeting of the European Society of Intensive Care Medicine and published simultaneously in JAMA.