Sleepless nights, circulatory problems, increased aggression: How heat waves strain the body, psyche and even entire economies.

The heat has Germany firmly in its grip these days. With temperatures approaching 40 degrees Celsius, as expected this week in the west and southwest, among other places, caution is advised. These temperatures can have life-threatening consequences, especially for certain people. As global warming increases, such heat waves are becoming more frequent and intense – and the risks are increasing.

Heat is hard work for the human body. The organism strives to maintain a constant temperature of around 37 degrees Celsius, as this is when most cells, proteins, and the immune system function optimally. Extreme fluctuations disrupt these processes. If the human body temperature rises above 42 degrees Celsius or falls below 32 degrees Celsius, it can be fatal.

A rule of thumb is: Danger arises when, under certain conditions, the body absorbs more heat than it can release. This is when body temperature gets out of control and rises rapidly. This threshold is highly individual and depends on age, health, activity, and habituation. At temperatures above 30 degrees Celsius, the body of many Central Europeans experiences significantly more stress cooling itself than at lower temperatures.

The cardiovascular system is under considerable strain in hot weather. People with chronic pre-existing conditions in this area should therefore be especially careful. As we age, body temperature regulation slows down and sweat glands become fewer, meaning the body's natural air conditioning system functions less effectively.

Since older people also feel thirst less frequently, they are at risk of dehydration. According to the Malteser Relief Service, even a one to two percent lack of water in the body can lead to headaches, fatigue, difficulty concentrating, and dizziness. Dehydration is also a risk for babies and young children, and sweat production is reduced.

When the body's sweating capacity reaches its limits, heat builds up: The body temperature rises rapidly – ​​often within 10 to 15 minutes – to over 40 degrees Celsius or more. As a result, the brain swells, leading to headaches, altered consciousness, or unconsciousness – a case for emergency medical services.

Heatstroke, on the other hand, causes a drop in blood pressure. This results in reduced blood flow to the brain, which can lead to symptoms ranging from weakness to nausea and dizziness, even unconsciousness. This, too, is an emergency.

According to the German Society of Neurology (DGN), heat also increases the risk of neurological diseases. A study by German neurologists published in the European Heart Journal concludes that the risk of stroke has significantly increased due to increasing nighttime heat.

Yes. According to estimates by the Federal Environment Agency and the Robert Koch Institute, approximately 3,000 people are expected to have died due to heat in 2023 and 2024—primarily people over 75 with pre-existing conditions such as dementia, cardiovascular, or lung disease.

According to the Federal Environment Agency, if it remains hot for several days in a row without any cooling at night, mortality continues to rise and reaches a consistently high level after about three to four days.

If temperatures don't drop below 20 degrees Celsius at night, they are referred to as tropical nights. Because the body can't recover sufficiently from the heat, sleep disturbances often result – and these, in turn, can have psychological and mental consequences.

Heat can make people more aggressive—which in turn increases conflict. A Japanese-South Korean study published in the Yale Journal of Biology and Medicine concludes that the risk of death from attacks increases by 1.4 percent for every degree increase in ambient temperature.

The number of aggressive incidents is increasing, resulting in more emergency admissions to acute psychiatric hospitals. According to the German Society for Psychiatry and Psychotherapy, Psychosomatics and Neurology (DGPPN), the number of suicides is even increasing.

Sebastian Karl, a physician at the Central Institute of Mental Health in Mannheim and co-author of a position paper by the German Society for Psychological Research (DGPPN), emphasizes: "Many people have experienced firsthand that they feel worse, sleep worse, or have difficulty concentrating when it's really hot: heat takes a toll on the psyche. As temperatures rise, the risk of mental illness also increases: by 0.9 percent per degree Celsius."

Researchers from Germany and Denmark provide a vivid example of how the brain is affected by heat in a study published in the journal "iScience": They analyzed more than seven million speeches by politicians from eight countries and concluded that speakers used less complex language on hot days. While simpler language can have positive effects for citizens, it is also an indicator of lower mental activity, the authors write.

National economies also suffer from heat: The Organization for Economic Cooperation and Development (OECD) has calculated the extent to which productivity declines due to heatwaves. In a special report, it concludes: Ten additional days with temperatures above 35 degrees Celsius lead to a decline in annual labor productivity of 0.3 percent. This effect is comparable to the productivity losses if energy prices were to rise by five percent. Longer heatwaves, in particular, have enormous impacts.

The Federal Environment Agency refers to studies that assume that during periods of high heat stress in Central Europe, productivity can be reduced by up to 12 percent due to more accidents at work, less concentration and the resulting errors.

If the room air temperature in workrooms exceeds the threshold of 26 degrees, the employer should take measures in accordance with the Workplace Ordinance – this becomes mandatory from 30 degrees.