Sleep in the heat
12.07.2026This summer brought new heat records, which directly affect people's nightly rest in Europe and the United States, forcing scientists to revise recommendations for the microclimate in bedrooms.
In the first weeks of July 2026, temperatures in many regions exceeded multi-year averages, and the accompanying humidity created conditions in which traditional cooling methods proved insufficient. The researchers focused on how these factors alter the natural course of sleep, when the body attempts to lower its core temperature to enter deep sleep phases.
Circadian rhythms and body temperature fluctuations
During the night, the human body's core temperature decreases under the influence of the circadian cycle. This process begins before falling asleep and reaches a minimum about six hours after a person falls asleep. After that, the indicator gradually increases, preparing the body for awakening. When the ambient air remains too warm, the cooling mechanism is disrupted, and the phases of slow-wave sleep and REM sleep are shortened.
In laboratory conditions, scientists have recorded that even a slight increase in temperature by two to three degrees above the comfortable level leads to an increase in the number of short-term awakenings. In 2026, when daytime highs reached 38–40 °C in central Europe, nighttime values often did not fall below 26 °C, which significantly complicated the natural decrease in body temperature.
Humidity as a key factor in discomfort
High relative humidity prevents sweat from evaporating, so the body can’t dissipate heat effectively. Research published in the journal Building and Environment found that the optimal humidity range for sleep is 40–60%. Beyond this range, sleep quality deteriorates regardless of air temperature.
In cities where air conditioning is not installed in all homes, such as in northern regions of Europe, residents are forced to rely on fans and open windows. However, when humidity is above 70%, this approach only increases the feeling of stuffiness. Portable dehumidifiers have become a popular solution for households without centralized HVAC systems.
Impact on children and adolescents
Children are more susceptible to heat stress because of their higher body surface area to mass ratio. A 2023 study by a lab at Auburn University and a follow-up in 2026 found that lower-income families often have bedroom temperatures above 75°F (24°C), even at night. This reduces the amount of slow-wave sleep that is responsible for restorative sleep.
In 2026, Texas and Arizona saw an increase in pediatrician visits for chronic fatigue and poor concentration among schoolchildren. Similar trends were seen in Spain and Italy, where summer vacations coincided with long periods of heat.
Socio-economic aspects of access to cooling
Not all households can afford to upgrade their air conditioning systems. In low-income areas, window air conditioners or fans are more likely to be used, which are less effective at removing moisture. This creates inequalities in sleep quality between different social groups.
Economists have estimated that installing a modern HVAC system in the average European home pays for itself within five to seven years through reduced healthcare costs and increased productivity. In 2026, the governments of Germany and France introduced subsidies for energy-efficient cooling systems for low-income households.
Recommendations for bedroom arrangement
The optimal air temperature in the bedroom is between 16,7–27,8 °C. To achieve these indicators, experts recommend using programmable thermostats that lower the temperature two hours before bedtime. Additional dehumidification of the air to 45–55% relative humidity ensures comfort even at temperatures of 24 °C.
It's also important to pay attention to your bedding. Natural fabrics like cotton or linen are more breathable than synthetic materials. Lightweight blankets filled with bamboo fiber help regulate heat exchange throughout the night.
Long-term health effects
Chronic sleep deprivation caused by heat increases the risk of cardiovascular disease, metabolic disorders, and weakened immunity. In 2026, the United States recorded an increase in hospitalizations for heart attacks in the elderly precisely during periods of prolonged heat.
For children, insufficient sleep affects cognitive development and emotional regulation. Psychologists have noted an increase in anxiety and irritability in adolescents who slept in overheated rooms during June and July.
Technological solutions of 2026
Manufacturers offer smart ventilation systems that automatically adjust airflow based on humidity and temperature sensors. Some models integrate with mobile apps and allow you to remotely change settings an hour before bedtime.
Major cities have opened community cooling centers where people can spend the night in comfort. Such initiatives have been implemented in Paris, Madrid, and Chicago during the hottest weeks of summer.
Research confirms that investing in quality bedroom cooling pays off not only in comfort but also in overall health. In 2026, scientists continue to collect data on the long-term effects of record heat on the quality of sleep of the population.
Sources
- Hinnant, B., Buckhalt, JA, Brigham, EF, Gillis, BT, & El-Sheikh, M. (2023). Socioeconomic disparities, nighttime bedroom temperature, and children's sleep. Journal of Applied Developmental Psychology, 86, 101530.
- Caddick, ZA, Gregory, K., Arsintescu, L., & Flynn-Evans, EE (2018). A review of the environmental parameters necessary for an optimal sleep environment. Building and Environment, 132, 11-20.
- Buckhalt, J. A. (2026). Sleep in a Heatwave. Psychology Today, July 5.
