While summers in northern India usually build up gradually, allowing the human body to adapt over weeks, the shift to extreme heat was abrupt this year, leaving little room for biological adaptation and putting people at greater risk of heat-related illness, experts have warned.
Dr Mugdha Tapdia, director of internal medicine at Fortis Hospital, Vasant Kunj, said: “The arrival of high temperatures earlier than usual puts stress on the body’s ability to adapt to hot weather, a phenomenon called seasonal or heat acclimation.”
Under normal circumstances, repeated exposure to heat over days or weeks triggers a series of physical responses: the body begins to sweat earlier and more efficiently, the heart rate decreases under heat stress, and the system becomes better at maintaining fluid and electrolyte balance. This physiological adaptation, which is referred to as heat acclimation, usually takes about one to two weeks of gradual exposure.
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“However, a sudden rise in temperature becomes more dangerous because the body’s natural acclimatization has not begun properly. The sudden rise is difficult for the body to tolerate and makes it difficult to regulate temperature, leading to rapid dehydration and loss of electrolytes. In these conditions, even healthy people become vulnerable to heat exhaustion and heat stroke,” said Dr Rajesh Rajan, Chairman, Indian Association of Clinical Cardiologists, and President of the Medical Doctors Association.
There is also the behavioral aspect. “Many people are yet to shift to summer routines such as increasing fluid or snack intake or adjusting outdoor schedules,” said Dr Manisha Arora, director of internal medicine at CK Birla Hospital.
This places excessive stress on the body, which can lead to heat stroke, heart rhythm disturbances, and other heat-related complications.
“Normally, hospitals start receiving cases of heat exhaustion in late May and June, when the heat wave properly begins. Patients usually experience intense sweating, dizziness, headaches, nausea, and muscle cramps. However, this year, cases started appearing in April itself,” Rajan said.
Dr Prashant Sinha, head of the emergency department at PSRI Hospital, said most of the patients suffered from severe dehydration, dizziness and heat exhaustion. “What makes this stage particularly risky is the body’s unpreparedness. April heat of this intensity leaves little time for physiological adaptation, increasing the likelihood of rapid deterioration.”
Vulnerable groups, such as the elderly, children, outdoor workers and those with heart or kidney disease, are more vulnerable to heat-related illnesses, experts said. “Babies lose fluids faster, and their inability to clearly express discomfort often delays intervention,” said Dr Sanjay K Jain, pediatrician and neonatologist and medical director at Makur Hospital.
How the body can still adapt
Experts stress that many risks can still be mitigated if people consciously allow their bodies to adapt to the heat.
“The method is simple. Start with 20 to 30 minutes outdoors during the cold hours and gradually increase the duration, with proper hydration,” Tapdia said, adding that mitigation efforts must move beyond individuals to institutions and employers.
“Employers can phase in shifts at the beginning of summer. Shade zones can ensure shaded areas and access to water. Schools can safely time outdoor activities rather than canceling them entirely. Heatwaves are predictable. Deaths from them are not inevitable. In a warming Delhi, survival will depend not only on escaping the heat but on learning how to live with it,” she said.
Ranjan recommended spending at least 30 minutes to an hour in a room without air conditioning or in a shaded area outside for about 20 minutes. “One should learn how to acclimatize by gradually getting used to the heat, increasing fluid intake, avoiding the hottest hours of the day, and wearing appropriate clothing,” said Dr. Sunil Rana, associate director and head of the department of internal medicine at Asian Hospital.
