# Does Heat Really Slow Your Thinking? What Research Says About Temperature and Cognition > Heat reliably lowers performance on cognitive tasks. Cedeño Laurent and colleagues (2018, PLOS Medicine) tracked 44 students in air-conditioned and non-air-conditioned dorms for 12 days during a Boston heat wave; the non-air-conditioned group had 13.4% longer reaction times on a color-word interference task and 13.3% lower throughput on addition and subtraction, and their recovery lagged after the heat wave ended. Goodman and colleagues (2020) used data on about 10 million U.S. test takers to show that a school year 1°F hotter reduces that year's learning by about 1%, with air conditioning offsetting most of the effect. Intelligence itself does not fall; what changes is the measurement condition. - URL: https://brainrank.jp/en/blog/heat-and-cognition - Published: 2026-09-08 - Publisher: BrainRank Editorial Team (https://brainrank.jp) - Tags: Cognitive abilities, Health On hot days concentration slips, arithmetic errors creep in, and text refuses to sink in. Most people have felt this, and it is not imagination. Recent summers have brought record heat, and lingering heat well into September has become normal. This article draws on studies that measured the effect of heat on cognition to explain what declines, by how much, and how to prepare for a test or exam. ## The heat-wave dormitory experiment The most direct evidence comes from [Cedeño Laurent and colleagues (2018, PLOS Medicine)](https://pubmed.ncbi.nlm.nih.gov/29995870/). In July 2016, as a heat wave hit Boston, they followed 44 students for 12 days: some lived in an air-conditioned dorm, the rest in an older building without air conditioning. The period covered five days before the heat wave, five days during it, and two days after it cooled. Every morning right after waking, students took two tasks on their phones. One was a color-word interference task (the Stroop task), which measures attention control and processing speed. The other was timed addition and subtraction, which measures working memory and processing speed. The result was clear. During the heat wave, students in the non-air-conditioned dorm had Stroop reaction times 13.4% longer and solved 13.3% fewer arithmetic problems than students in the air-conditioned dorm. The easily overlooked finding is the lag in recovery. Even after outdoor temperatures fell, the non-air-conditioned building stayed warm inside, and performance did not bounce back immediately. It is not "fine once the heat passes"; the effect persists until the building sheds its heat. The participants were healthy young adults. Older people and those with chronic conditions have less thermoregulatory reserve, so the effect may be larger for them. ## A year's worth of learning is affected too Heat affects not just a single day's score but what accumulates. [Goodman and colleagues (2020, American Economic Journal: Economic Policy)](https://www.aeaweb.org/articles?id=10.1257/pol.20180612) analyzed data on about 10 million U.S. students who took the PSAT college-admissions test more than once, relating the temperatures they experienced in the year before a test to their score gains over that period. They found that a school year 1°F (about 0.56°C) hotter reduces that year's learning by about 1%. The effect was concentrated in years with many hot days, and air conditioning at school or at home offset most of it. The harm from heat, in other words, is not inevitable; it is the kind that the environment can prevent. The same authors report that the effect is larger for low-income and minority students. This is where the argument that access to air conditioning feeds learning gaps comes from. ## Why heat dulls thinking There is no single mechanism; several are thought to overlap. - Thermal discomfort steals attention: brain resources go to coping with heat (thermoregulation, processing discomfort), leaving less for the task - Sleep quality falls: hot nights delay sleep onset and reduce deep sleep. Next-day declines sometimes run through sleep loss rather than heat itself (see [sleep and cognition](https://brainrank.jp/en/blog/sleep-and-cognition)) - Dehydration: fluid loss of even 1 to 2% of body weight has been reported to lower attention and short-term memory performance - Mood and motivation: in an unpleasant environment, persistence drops and people give up earlier on hard problems How much each route contributes is still being worked out. For practical purposes, though, whatever the route, lowering the room temperature, sleeping well, and drinking water block several of them at once. ## What happens to an IQ test score The point worth keeping straight is that heat lowers the day's performance, not ability. IQ expresses your relative position within your age group, and taking a test on a hot day does not move that position. What changes is the measurement condition. The tasks most affected are those demanding processing speed and sustained attention. In formats that require solving many items within a time limit, or [classification](https://brainrank.jp/en/problems/classification) tasks that hinge on spotting fine differences, a 13% slowdown visibly cuts the number of items completed. [Logical reasoning](https://brainrank.jp/en/problems/logic), where you can take your time, is likely affected less. As explained in [the processing-speed article](https://brainrank.jp/en/blog/processing-speed-training), processing speed is the domain most sensitive to your state. So if an IQ test taken in a hot room comes out low, treat it as measurement error, not a change in ability. Put the other way, retaking it under good conditions brings you closer to your true position. ## Preparing for a test or exam on a hot day The steps the research supports are all unglamorous, but each has a basis. - Lower the room temperature: the biggest single effect. If air conditioning is unavailable, use a fan and block sunlight to limit the rise - Cool your body before starting: cool your neck and wrists, have a cold drink. Do not start with an elevated body temperature - Drink water regularly: small amounts before you feel thirsty - Sleep in a cool room the night before: sleep lost on a hot night shows up directly in the next day's performance - Choose the time of day: if you can, take the test in the cooler morning hours - Allow for lagged recovery: the day after an extreme-heat day, buildings and bodies may still hold heat ## Measure your real score in a cool room If you want to know your cognitive profile, setting up the measurement conditions is the first step. [BrainRank's free IQ test](https://brainrank.jp/en/start) scores 20 questions (about 10 minutes) across four domains, spatial reasoning, pattern recognition, logical reasoning, and classification, using item response theory (IRT), and returns your profile by domain. Taking it in an air-conditioned room, in the morning after a good night's sleep, is the way to get a result closest to your true position. Results are estimates for entertainment and self-understanding, not a medical or diagnostic assessment. ## Frequently asked questions ### Does heat really dull your thinking? Yes. During a heat wave, students living in a dorm without air conditioning had reaction times about 13% longer and solved about 13% fewer arithmetic problems than students in an air-conditioned dorm. Their performance also took days to recover after the heat passed. ### Does heat lower IQ? Your relative position, which is what IQ expresses, does not change. But a test taken in a hot environment will score lower, mostly on tasks that require processing speed and attention. That is a worse measurement condition, not a loss of ability. ### How should I prepare for a test or exam on a hot day? Lowering the room temperature (air conditioning or a fan) is the most effective step. Beyond that: cool your body before starting, drink water regularly, sleep in a cool room the night before, and if you can, take the test in the cooler morning hours. ## Sources - [Cedeño Laurent and colleagues (2018, PLOS Medicine)](https://pubmed.ncbi.nlm.nih.gov/29995870/) - [Goodman and colleagues (2020, American Economic Journal: Economic Policy)](https://www.aeaweb.org/articles?id=10.1257/pol.20180612) --- Statistics and percentages are calculated from a normal distribution model with a mean of 100 and a standard deviation of 15. The tests on this site provide estimates for entertainment and self-understanding; they are not medical or clinical assessments, nor official intelligence tests. When citing, credit "BrainRank (brainrank.jp)" and link the article URL.