The summer of 2026 set a record for high temperatures and heat-related deaths in Europe and the US, with older adults and those with chronic health conditions the most affected, but everyone will be affected to some degree. A great deal of research has been done to investigate how high temperatures and humidity affect the quality of our sleep. This is a good time to summarize what we know.
First, let’s look at what happens to body temperature during a normal night’s sleep. Regulated by the circadian cycle, our core temperature drops slightly when sleep begins and continues to drop, reaching its lowest point about six hours later. Most of us relate to sleeping with only a sheet and waking up to get a blanket. This decrease is caused by a slower metabolic rate and less heat production. After the low point, body temperature begins to rise as part of the circadian process leading to awakening. Controlling the ambient temperature in the bedroom is essential to support good sleep. Because northern European countries have fewer air conditioners in homes and apartments than in the United States, it is more difficult to cool down to a comfortable temperature there.
How humidity and airflow affect sleep quality
High humidity mixed with heat is especially uncomfortable, and we’re all familiar with the heat index, or what’s sometimes called “the real feeling.” A high-quality whole-house HVAC system draws heat and moisture from the home and cools it. Good air flow and ventilation are also essential for optimal sleep. Window units are less efficient, and window or ceiling fans are even less so. Portable dehumidifiers are economical and effective in homes without a good HVAC system.
When researchers manipulated temperature and humidity and measured sleep (time to fall asleep, number and duration of nighttime awakenings, REM and slow wave periods and total duration), they concluded that a bedroom temperature of 62 to 82 degrees Fahrenheit and a relative humidity of 40% to 60% are most conducive to good sleep. Of course, there are individual differences that can sometimes cause difficulties, as is often the case when two or more people share a bedroom, bed and bedding.
Why is better cooling good for health?
Children are more susceptible to the adverse effects of high temperatures and humidity than adults because of their higher body surface-to-mass ratio. Research from our lab at Auburn University has shown that families with limited financial resources often lack good nighttime bedroom temperature control and children sleep worse.
As we know that poor sleep can cause or exacerbate many health problems, high heat and humidity can affect health directly and indirectly through poor sleep. For those who can afford it, installing new cooling and dehumidification systems or upgrading existing ones is a good investment not only for comfort, but also for health.
