Almost every home and office in Israel fights the same summer battle: one person is sweating, another is freezing, someone lowers the air conditioner and someone else raises it. In the end, everyone is convinced they are right.
But the question of where to set the AC is not only about comfort, relationships or the electricity bill. In the Israeli summer, the temperature we live and sleep in affects the body more than many people realize, from sweating and dehydration to blood pressure, heart rate, concentration, fatigue and sleep quality.
“Studies in recent years strengthen the direct link between high temperatures and impaired sleep quality,” says Dr. Joanna Malka, an emergency medicine specialist at Meuhedet’s Central District.
According to Malka, a broad scientific review published in 2024 found that higher indoor and outdoor temperatures are consistently linked to shorter and poorer sleep, especially during hot seasons and among vulnerable populations such as the elderly and people with chronic illnesses.
“The main reason is that the body has difficulty carrying out the natural cooling process required to enter the deep and restorative stages of sleep,” she explains.
The result can be a night that looks like sleep from the outside, but does not really recharge the body. “We may wake up many times during the night, even if we do not remember it in the morning,” Malka says. “Sleep becomes more superficial, deep sleep is shortened and we wake up tired despite spending many hours in bed.”
Heat also affects the body during the day. “The body needs to invest energy in cooling itself,” says Dr. Dean Richter, an internist at Clalit Health Services. “Our body has thermoregulation, meaning it must maintain a normal body temperature.”
The first sign is usually sweating, which causes fluid loss. If people do not drink enough, it can lead to dehydration and changes in electrolyte balance. Heat also causes peripheral blood vessels to expand so the body can release heat through the skin. As a result, blood pressure may drop, causing dizziness, weakness or a feeling of faintness. The heart rate then rises to compensate.
High heat can also make people slower and less focused. “When temperatures are high, there is a significant decline in reaction time, decision-making and accuracy in performing tasks,” Richter says.
But setting the AC too low is not harmless either. Cold, dry air can dry the mucous membranes in the nose and airways, weakening the body’s first line of defense. “The cold itself does not contain viruses,” Richter says, “but dry and damaged mucous membranes make it easier for viruses to enter the body.” In people with asthma or COPD, cold and dry air can also trigger attacks. Cold may also cause muscle tightness, neck pain, back pain or joint pain.
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So why does one person freeze while another sweats in the same room? Richter says temperature perception depends on muscle mass, fat mass, sex, hormones, age, metabolism, blood flow, sleep, stress and even diet. The number on the remote is objective, but the way the body experiences it is personal.
For daytime use, Richter says health organizations generally recommend setting the AC to 24°-25°C (75°-77°F). This range is usually comfortable for most people, avoids extreme cold and also saves electricity, since every degree lower in summer significantly increases AC power consumption.
At night, Prof. Yaron Dagan, head of sleep medicine at Assuta and Maccabi Health Services, says there is no single magic number. Body temperature naturally drops during the night as part of the biological clock, and anything that disrupts that process can disturb sleep.
“You cannot say 25°C (77°F) or 22°C (72°F),” Dagan says. “It is very individual. A person needs to feel that the temperature is comfortable and pleasant, not too cold and not too hot.”
The bottom line: sleeping with AC should not turn the bedroom into a refrigerator, but the body should not be left fighting the heat either. A cool, dark room, enough fluids during the day and regular sleep hours can make the difference between months of fatigue and a summer in which the body can function properly.