Why does about 23°C act like a turning point?
The simplest way to read the evidence is that 22–24°C is a comfort zone rather than a magic number. A systematic review of 17 workplace studies concluded that optimal cognitive functioning generally falls between 22°C and 24°C, and that temperatures above 24°C can degrade performance [1]. That framing implies a two-sided effect: moving up toward the band from a cooler room is not harmful, but pushing past it is.
One experiment on female higher-education students in a hot climate found that the best concentration occurred at 23°C, which fits the idea of a peak near the middle of that band rather than a steady climb with warmth [4]. Office research likewise describes a range in which people can hold cognitive performance steady, with measured effects on short-term performance varying across that zone—from a slight dip at 23°C to a modest gain elsewhere within it [5]. The practical reading is that 23°C is close to the upper edge of the helpful region, not the start of a decline.
Which mental skills feel the heat first?
Not all thinking is equally temperature-sensitive. The systematic review found reaction time and processing speed to be the most sensitive skills to elevated ambient temperatures, while higher cognitive functions such as logical and abstract reasoning were more resistant [1]. In plain terms, a warm room is more likely to slow you down on a fast, timed task than to stop you from solving a difficult problem.
That pattern matters for how the 23°C threshold should be interpreted. If the tasks that suffer above 24°C are speed-based, then the cost of a warm office may show up as slower responses and reduced throughput rather than obvious errors on complex judgments [1]. The review's authors note that this could matter in work settings where rapid decisions are made, though they caution that the included studies had limited ecological validity—meaning they may not fully reflect real workplaces [1].
What do brain recordings add to the picture?
Physiological measurements offer a possible mechanism, though the evidence is correlational. In a summer climate-chamber experiment testing temperatures from 24°C to 32°C, alpha-band activity in the occipital lobe—a brain rhythm linked to relaxed wakefulness—peaked at 26°C, and whole-brain alpha power was higher when participants reported thermal comfort than when they reported discomfort [2]. The study also found that beta, delta, and theta band power correlated with scores on a concentration-focused test [2]. This is consistent with temperature affecting attention-related brain activity, but it does not establish that temperature causes the performance change.
A separate chamber study with college students found gender differences in skin temperature and in an EEG-based concentration index, with the concentration index more affected by cold in male subjects, and confirmed that this index shifts with indoor temperature [3]. Notably, that study reported that the effect of temperature on performance depended on the type of cognitive task [3]—reinforcing the review's point that some skills are more vulnerable than others.
How firm is the 23°C line?
The threshold is a useful rule of thumb, not a sharp cliff. The systematic review itself describes results as inconsistent across studies, even while identifying 22–24°C as the general optimal range and flagging above-24°C heat as a risk [1]. The office study's effects within the comfortable zone were small—on the order of a fraction of a percent to about one percent—suggesting that near 23°C the stakes for short-term performance are modest [5].
The bigger uncertainty is about real-world settings. Much of the evidence comes from controlled chambers and short tasks, and the review explicitly notes limited ecological validity as a reason unequivocal conclusions are difficult [1]. So the safest summary is directional: warming a cool room toward roughly 23°C is unlikely to hurt and may help, while pushing well above 24°C is where performance, especially speed, is most likely to suffer [1][4].
Sources used in this answer
[The impact of high indoor temperatures on cognitive performance within the work setting: a systematic review].
A systematic review of 17 workplace studies found the optimal temperature range for cognitive functioning is generally 22–24°C, with reaction time and processing speed most sensitive to heat and higher reasoning more resistant, though results were inconsistent and ecological validity limited.
The relationship between thermal comfort, performance, and electroencephalogram during cognitive tests at normal indoor temperatures in summer
In a summer chamber experiment from 24°C to 32°C, occipital alpha-band power peaked at 26°C, whole-brain alpha power was higher during thermal comfort, and beta, delta, and theta power correlated with concentration-test scores.
Exploring the effects of indoor temperature on college students’ physiological responses, cognitive performance and a concentration index derived from EEG signals
A chamber study of college students found gender differences in skin temperature and an EEG-based concentration index, that temperature effects on performance depended on task type, and that the concentration index was more affected by cold in male subjects.
Combined effects of ventilation rates and indoor temperatures on cognitive performance of female higher education students in a hot climate
Among female higher-education students in a hot climate, the best concentration occurred at 23°C.
Indoor temperature and office work performance in a temperate climate
Office workers can maintain cognitive performance within a comfort zone, with short-term performance effects ranging from about –0.1% at 23°C to a maximum of 1.2% within that zone.