This summer has already been intense. In just the first 10 days of April 2025, Maharashtra reported 34 heat stroke cases. Yet, this number likely captures only a small fraction of the actual disease and death burden caused by extreme heat. Extreme heat can harm the human body in 27 different ways, leading to serious consequences, including death. It is often difficult to attribute an individual illness event or death to heat exposure. Hence, the official numbers tend to under-estimate the actual scale of illnesses and deaths from heat. For example, in 2019, Maharashtra officially reported 9 deaths caused by heat stroke. But the Global Burden of Disease study estimates that nearly 16,000 deaths that year were linked to extreme heat, accounting for nearly 2% of all the deaths in the state in that year.

This underestimation of heat-related impacts can have serious consequences. It can lead to inadequate policy responses, lacking both strong legal mandates and sufficient funding. It can also result in a disproportionate focus on short-term measures which may be effective in addressing the more visible heat strokes; while the long-term measures needed to address the full scale of health risks posed by extreme heat are overlooked.

This underestimation also reinforces the common belief in India that we are tough enough to handle heat. Most Indians may have a higher tolerance to heat. However, extreme temperatures and humidity levels now being recorded in many places in India, exceed what the human body can endure, even with acclimatization. This perception gap is crucial because the best way to prevent heat-related illness is to avoid exposure. But if the severity of the threat is not fully recognized, people may not take the necessary precautions. 

This article discusses the wide-ranging health impacts of extreme heat, the challenges in accurately tracking these effects, and how these gaps affect the policy responses.

Photo credit - Swapnil Patil, Prayas (Energy Group)

Different strokes

The human body operates within a narrow temperature range around 37°C. When heat pushes the body beyond this threshold, it initiates various cooling mechanisms such as sweating and increased blood supply to the skin, to maintain temperature. If the body fails to cool down effectively, health is impacted. The impact of heat varies depending on how intense is the heat, how long are you exposed to it, and how well can your body cope with it. In some cases, the impacts may be mild, such as rashes, cramps, or fainting. But in more severe cases, it can lead to heat strokes or multi-organ failures.  

Heat strokes are classified into two types: exertional and classic. They are marked by clinical features such as very high body temperature and central nervous system dysfunction (confusion, disorientation, seizure or even coma). If rapid and timely cooling measures are not taken up, heat stroke can be fatal. 

In India, much of the attention is directed towards exertional heat strokes. Exertional strokes typically occur when individuals are doing strenuous activity in hot conditions.  It develops quickly, often within a couple of hours. Young and physically fit individuals are more vulnerable. This is partly because they may believe they can tough it out, trusting their physical strength to get them through. This type of stroke is often seen among people who are required to work in the heat for their livelihoods like farmers and labourers. Athletes are also vulnerable.

Classic heat strokes are seen during days of extreme temperatures or a heat wave. Vulnerable groups such as children, pregnant women, the elderly, and those with other co-existing health conditions are more at risk. These individuals tend to have reduced thermoregulatory capacity, meaning their bodies are less effective at maintaining a safe internal temperature in extreme heat. Unlike exertional heat stroke, where the body temperature spikes rapidly, classic heat stroke develops more gradually, with the core body temperature rising over several hours or even days. The body does not get enough time to cool down, especially during consecutive hot days and warm nights, like those experienced in Maharashtra (and elsewhere) in 2024, which significantly increases the risk. This form of heat stroke disproportionately affects people living in low-income urban settlements, where homes are often poorly ventilated and lack access to cooling.

A much less known feature of heat-related health impacts is its impact on multiple organ systems. As discussed earlier, sweating and increased blood supply to the skin are the two main thermoregulatory mechanisms the body uses to dissipate heat. During excessive heat stress, these put strain on the cardiovascular, kidney, and metabolic systems.  For example, one recent study found that Chronic Kidney Diseases from unidentified causes is rising among outdoor workers in Tamil Nadu with extreme heat exposure as one of the most likely causes. Studies from several cities in India report an increased risk of death on the same or subsequent days when temperatures cross a particular threshold. These deaths occur mostly due to heart, lung, or kidney dysfunction, exacerbated/triggered by extreme heat. The risk is much higher among elderly or people with pre-existing diseases. Population-level data on deaths or emergency admissions (when correlated with daily temperatures) are useful to assess the mortality burden due to extreme heat. However, at the individual case level, attributing extreme heat as a cause for any such death is extremely challenging.   

Keeping track

Tracking the impacts of extreme heat is crucial as it reveals the true scale and severity of heat-related risks. This visibility can drive more serious and sustained policy action. A recent study highlights that government officials themselves believe that making heat-related deaths more visible is key to triggering a stronger response. Better tracking also enables real-time decision-making, allowing authorities to respond more effectively during heat waves. However, it is easier said than done. 

Diagnosing heat stroke can be challenging. Its symptoms often resemble other conditions like infections, or neurological disorders. Definitive diagnosis of such conditions requires detailed investigations which take time. It also requires taking cognizance of immediate environmental conditions (temperature and humidity). Health workers need specific training and must remain constantly aware of these factors. Without a high level of vigilance and suspicion, many cases of heat stroke can go undetected.

The Ministry of Health and Family Welfare (MoHFW) has issued clinical guidelines to help identify and manage heat stroke more effectively.  It has separate guidelines for conducting autopsies in suspected heat stroke cases. The ministry has also put a national level heat related illness and death surveillance system in place, where public health centers are required to report daily data to a centralized system. However, the data is not publicly available. According to MoHFW, public health facilities across India reported approximately 48,000 suspected heat stroke cases during March to July 2024, along with 269 suspected and 169 confirmed heat stroke deaths.

However, the official numbers are likely to be significantly under-reported. A recent compilation of media articles estimated media reporting of around 733 deaths from heat strokes across 17 states during the three summer months of 2024. This is more than double the official number for the entire summer of 2024. And the true toll may be even higher. 

There are several reasons for this gap. Many healthcare professionals are still not fully aware of the protocols issued by MoHFW for diagnosing and reporting heat stroke. As discussed earlier, it is difficult to diagnose heat stroke. Assigning it as a cause of death is even more challenging. It needs an autopsy with advanced tests which may not be available everywhere. In some cases, pressure may be exerted on medical staff to avoid attributing a death to heat, especially if it might expose an employer or event organizer to legal consequences. Moreover, the national heat health surveillance system only collects data from public health centers. The participation of private health facilities is poor. Private practitioners deliver a significant share of health care, especially in urban areas.

The most critical reason for underreporting, perhaps, is that only exertional heat strokes are likely to be recognized and recorded. In such cases, it is relatively easier to link the symptoms to heat, as the immediately preceding environmental context, such as if the patient has been working outdoors in intense heat, is usually known. In contrast, classic heat strokes often go unnoticed and unreported, especially when the symptoms develop slowly. Attributing extreme heat as the cause becomes even more challenging when death results from cardiovascular, respiratory, or renal system collapse triggered by high temperatures.

For example, during our field assessment in Pune district, we came across a case of a woman with diabetes and hypertension who was working in the fields under intense afternoon heat. She felt dizzy and collapsed. Locals gave her water and took her home. That evening, she became restless and was taken to a hospital. Despite medical attention, she died an hour later of cardiac arrest. While heat likely played a role in worsening her condition, her official cause of death was probably recorded as death due to cardiac event, with no mention of heat exposure. There would be many such cases.

In order to overcome the challenges of bottom-up tracking, researchers have used all-cause death data to identify surges in daily deaths that correlate with rising temperatures. A recent study analysed this data from 2008 to 2019 for 10 cities in India and found a 14.7% increase in daily mortality attributable to extreme heat. Another analysis extrapolated these findings to all the districts in India and estimated annual excess deaths of about 1.5 lakhs each summer during 2008-19. Global Burden of Disease is an international research collaborative that quantifies the impacts of hundreds of diseases, injuries, and risk factors across the globe. It shows an increasing trend of deaths attributed to heat in India, with the latest (pre-COVID-19) estimates of 2.28 lakh deaths in 2019. All these numbers underscore the massive gap between the official numbers and the true health impact of rising temperatures. 

Unfortunately, Indian municipalities and health departments do not publish daily all-cause death data, neither in real-time nor with a short delay. Regular and timely publication of such data would help in better estimation of the real extent of the impacts of heat on Indians. Most of the cities in India have a fairly well-working digital registration of deaths. This was evident during the COVID-19 pandemic when daily death bulletins were published. However, most of the cities have since discontinued it. 

Short term Vs Long Term 

India is already adopting several interventions at the national, state, and local levels to deal with heat-related health risks. However, most of them are driven by the narrow focus on the more visible exertional heat strokes. Most heat action plans revolve around maximum temperature warnings and public advisories urging people to stay indoors, stay hydrated, and take frequent breaks. Health system preparedness is similarly geared towards managing acute cases, with provisions like cooling beds, ice packs, and increased ambulance readiness during heat waves. 

While these interventions are necessary, they do not address the true scale of the effects of heat, particularly on vulnerable populations such as the elderly, those with chronic conditions, and low-income communities living in poorly ventilated housing. A large section of Indian population works outdoors in the informal sector. Many of these workers have no option but to risk their health by continuing to work in harsh temperatures. We need long-term structural solutions to deal with the actual impact of the heat. These solutions would include better urban planning to reduce heat retention in cities, mass adoption of climate-resilient buildings that ensure thermal comfort without excessive energy use, greening of the cities, and wider access to affordable and energy-efficient cooling technologies. Such measures are undoubtedly more complex and resource-intensive, but they are essential to deal with the worsening heat problem. 

In conclusion, the current focus on the more visible exertional heat strokes, while important, is narrowing the scope of India’s response to extreme heat. This limited attention overlooks the widespread and often deadly impacts of classic heat strokes and multi-organ failures, which are occurring at a much larger scale than recognized. Although a national surveillance system exists, it needs significant strengthening, particularly through improved diagnosis, reporting, and the timely public release of all-cause death data by municipalities. To truly address the growing threat of heat, we must shift from reactive, short-term measures to sustained, long-term strategies that reduce overall vulnerability and build systemic resilience.