A new wave of extreme heat is sweeping across the United States during the Independence Day holiday period, just days after Europe experienced record-breaking temperatures, prompting renewed concerns among scientists and health experts about whether the human body can adapt to an increasingly warming climate.

Large parts of the central and eastern United States are under heat warnings, with temperatures expected to range between 100°F and 115°F (37.8°C–46.1°C) over the July 4 weekend. The dangerous conditions follow an unprecedented late-June heat wave across Europe, where France, Spain, the United Kingdom, Belgium, the Netherlands, Switzerland, and Germany all recorded exceptionally high temperatures.

Germany’s national weather service (DWD) said the country had never experienced such prolonged and intense heat so early in the year.

Health experts warn that extended periods of extreme heat place significant stress on the human body, particularly when daytime temperatures exceed 30°C (86°F) and nighttime temperatures remain above 20°C (68°F). The greatest risks are faced by older adults, young children, pregnant women, people with chronic medical conditions, and outdoor workers.

Professor Claudia Traidl-Hoffmann, Director of the Institute of Environmental Medicine at the University of Augsburg and Helmholtz Munich, said the human body possesses some ability to adapt to heat, but such adaptation occurs over centuries rather than years.

According to Traidl-Hoffmann, the body's cooling mechanisms begin activating when outdoor temperatures reach approximately 23°C (73.4°F). Blood vessels expand to release heat while sweating helps cool the body and maintain a stable internal temperature.

However, when these mechanisms become overwhelmed, the consequences can be severe. Heat-related illnesses can progress from cardiovascular complications and heat stroke to multiple organ failure. If the body's core temperature rises to around 42°C (107.6°F), extensive cellular damage occurs, potentially leading to death without immediate medical treatment.

Researchers also believe that extreme heat negatively affects the lungs by accelerating inflammatory processes, making individuals more susceptible to respiratory infections, although the precise biological mechanisms remain under investigation.

Medical experts emphasize that preparation for heat waves should begin well before summer. Traidl-Hoffmann recommends that people with chronic illnesses consult healthcare providers early in the year to review medications and ensure existing conditions such as allergies or eczema are well controlled before temperatures rise.

During periods of extreme heat, specialists advise staying well hydrated, consuming light plant-based meals, avoiding alcohol and smoking where possible, and maintaining sufficient sleep to help the body recover from heat stress.

Although younger, physically fit individuals generally tolerate heat better than older or medically vulnerable people, scientists caution that there are biological limits to human adaptation.

"The rapid increase in the number of extremely hot days is occurring faster than both humans and ecosystems can adapt," Traidl-Hoffmann warned, underscoring growing concerns that climate change is increasing both the frequency and intensity of heat waves worldwide.