When the sun blazes outside and temperatures soar, many people choose to seal off their apartments—keeping windows closed and using curtains or blinds to block direct sunlight. Experts often recommend this approach to keep indoor spaces as cool as possible, especially for those who are away from home during the day.
Heat Indoors Poses Special Risks for Older People
For seniors who remain at home during the day, however, this strategy can pose risks. When a home is sealed off completely, carbon dioxide levels and humidity inside rise. This can put strain on the cardiovascular system and, in the worst case, lead to circulatory collapse, as the German Working Group for Air Hygiene reported on the platform X.
Sweating Raises Indoor Humidity Levels
As the body sweats to prevent overheating, indoor humidity automatically rises. Additionally, warm summer air can hold more moisture because warm air absorbs higher amounts of water vapor. Whether ventilation makes sense depends, according to Gudrun Laschewski from the Center for Medical-Meteorological Research at the German Weather Service (in an interview with #Faktenfuchs by BR24), on the difference between outdoor and indoor humidity and the effectiveness of air exchange.
If the air outside is drier than indoors, ventilating can reduce humidity levels, especially if noticeable air exchange occurs. However, if outdoor humidity is higher, ventilating would increase the moisture content inside the apartment. Besides humidity, temperature and air circulation also influence how well the body can sweat and dissipate heat.
Why Humidity Is Crucial for the Body in Hot Weather
When temperatures rise, the body works hard to cool itself—primarily through heavy sweating and increased heart performance, as Professor Martin Scherer from the University Medical Center Hamburg-Eppendorf explained in an interview with #Faktenfuchs. The circulatory system must exert considerable effort to maintain the body’s “cooling mechanism.”
Sweat evaporates from the skin and provides cooling. However, if humidity is high, this process is hindered, placing additional stress on the body, particularly for older individuals. For people with pre-existing conditions or certain medications, tolerance to heat may be reduced by several degrees, Scherer added.
If the body can no longer cope with the strain, the consequences can be life-threatening. Initial signs of overheating include weakness, dizziness, elevated pulse, fever, and confusion.
Ventilating During the Day—Yes or No?
Whether ventilating during the day in hot weather is advisable depends on several factors. Professor Scherer referred to common sense: if the outdoor temperature is lower than the indoor temperature, ventilating is beneficial. If it is hotter outside, windows should remain closed to keep the heat out.
There is no general recommendation to “always open or always close windows.” According to current knowledge, ventilating at night is preferable since temperatures usually drop. During the day, experts recommend keeping sun-facing windows closed and darkened with blinds or curtains, as advised by the Federal Environment Agency.
Still, fresh air must enter the home: “People need oxygen. Therefore, rooms should be supplied with fresh air daily through natural ventilation,” emphasized Hans-Guido Mücke from the Federal Environment Agency.
Appropriate measures include tilting windows while keeping them shaded and creating cross-ventilation to improve air circulation. However, universal rules cannot be established because factors such as the apartment’s location or personal comfort must also be considered.
How to Protect Yourself During Extreme Heat
Prolonged heatwaves can seriously affect health. What can help to stay safe?
General Tips:
– Drink enough fluids—at least 1.5 to 2 liters daily.
– Maintain contact with relatives or neighbors to get help in emergencies.
– Never leave children or animals in a parked car, as temperatures inside rise rapidly to dangerous levels.
At Home:
– Stock up on drinks.
– Prefer light meals such as fruits, vegetables, and salads. Salty foods and mineral water help replenish lost minerals.
– Darken windows and ventilate preferably early in the morning or at night.
– Regularly cool wrists, neck, or calves with cold water.
– Take lukewarm showers, as cold showers may hinder the body’s heat dissipation.
– Create shaded seating areas on balconies or terraces.
– Consult a doctor about necessary medication adjustments.
– Conserve water in household and garden use as much as possible.
Outdoors:
– Use sun protection such as high-SPF sunscreen.
– Avoid direct sunlight; choose shady paths and wear a hat.
– Stay indoors during the hottest part of the day (afternoons).
– Wear loose, light-colored clothing.
– Schedule physical exertion like sports or shopping for early mornings or evenings.
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