From Dehydration to Heatstroke: How Heatwaves Take a Toll on Your Health

India is already in the grip of an intense summer, with temperatures soaring to punishing levels and heatwave alerts issued across several regions.

According to data from AQI.in, 19 of the world’s 20 hottest locations are currently in India — a stark reminder of how extreme the conditions have become. Surviving such heat is no longer as simple as staying indoors or drinking water — especially for those who must step out for work or daily life.

To understand how heatwaves impact the human body, we spoke with Dr Vimal Pahuja, MD and Associate Director of Internal Medicine at Dr LH Hiranandani Hospital.

Early Signs Often Go Unnoticed

Dehydration doesn’t always announce itself loudly. It can begin with subtle symptoms that are easy to ignore — persistent fatigue, irritability, or even difficulty concentrating.

Beyond a dry mouth, warning signs include reduced urination, darker urine (closer to apple juice than lemonade), and sudden headaches or dizziness when standing. These symptoms indicate falling blood volume — the body’s early distress signal.

A Rapid Slide Towards Heatstroke

Dehydration is often the first step in a dangerous chain reaction. When the body loses its ability to cool itself through sweating, heat exhaustion can set in quickly — sometimes within an hour of exposure.

If the core body temperature crosses 40°C (104°F), it can lead to Heatstroke, a life-threatening condition. At this stage, the brain’s temperature regulation fails, and vital organs can begin to shut down within minutes.

The ‘Thirst Gap’ Problem

One of the biggest dangers is that thirst lags behind dehydration. Most people don’t feel thirsty until they’ve already lost around 2% of their body’s fluids.

In older adults or individuals under stress, this delay becomes even more pronounced, meaning the body may already be struggling by the time you feel the urge to drink water.

Who Is Most at Risk?

Heat doesn’t affect everyone equally:

Children absorb heat faster but sweat less efficiently.
Elderly individuals have reduced ability to regulate temperature and often take medications that worsen dehydration.
Outdoor workers face continuous heat exposure, giving their bodies little time to recover.
Women tend to have higher heat-related mortality rates due to physiological and hormonal factors.
Long-Term Damage Is Real

Heatwaves don’t just cause short-term illness. Repeated exposure can have lasting consequences.

Chronic heat stress has been linked to Chronic Kidney Disease due to repeated strain on kidney function. It can also increase the risk of hypertension and heart disease by placing ongoing stress on the cardiovascular system.

How to Stay Safe

Simple awareness can make a crucial difference:

Check hydration levels: Try the pinch test — if your skin doesn’t quickly return to normal, you may be dehydrated.
Don’t wait for thirst: Sip water regularly, ideally every 20 minutes.
Replenish electrolytes: Sweating drains essential salts, so fluids with electrolytes are important during extreme heat.