Every May and June, our lab sees a sudden rise in patients walking in with weakness, low urine output, and abnormal kidney reports — all because the body simply could not keep up with the heat. Here is what you should know, written the way I would explain it to a patient sitting across my desk.

First, understand what is really happening inside the body

When it is 44°C outside and you are stuck in traffic or working in the sun, your body is doing one job above everything else — keeping your core temperature near 37°C. It does this by sweating. But sweat is not just water; it contains sodium, potassium, and chloride. Lose too much of it, and three things start going wrong at the same time: your blood pressure drops, your kidneys get less blood supply, and your brain starts misfiring.

Heat exhaustion is the warning stage. Heat stroke is when the warning was ignored. The difference between the two can be twenty minutes.

Early warning signs you should never brush off

People often tell me, “Doctor, I just felt a little weak, so I sat down.” That is exactly the moment to act. Watch for these:

• Heavy sweating that suddenly stops — this is a danger sign, not relief
• Headache that feels like a tight band, with mild nausea
• Muscle cramps in the calves, thighs, or abdomen
• Dizziness when you stand up, or a feeling that the room is tilting
• Dark yellow urine or no urge to urinate for several hours
• Fast heartbeat even while sitting still

What to do in the first 10 minutes

If you or someone near you is showing these signs, do not wait for a doctor to arrive. Start treatment yourself:

• Move the person to the coolest place available — a room with AC, or at least shade with a fan
• Loosen tight clothes; remove belts, shoes, anything restrictive
• Wet a cloth and place it on the neck, armpits, and groin — these areas have large blood vessels close to the skin and cool the body fastest
• If the person is conscious, offer sips of ORS or plain water with a pinch of salt and sugar. Never force fluids on someone who is drowsy or confused — they can choke
• Call an ambulance if temperature stays above 39°C after 10 minutes of cooling, or if the person remains confused

Who is at the highest risk — and the people we worry about most

In my experience, the patients who suffer the worst outcomes are not the young men working construction (though they are at risk). It is the people whose families assumed they were fine:

• Elderly parents living alone, who often turn off the fan to save electricity. If they are on calcium or vitamin D supplements, dehydration also worsens bone-muscle weakness — see our note on calcium and vitamin D testing after age 35.
• Small children left in cars even “for just five minutes”
• Pregnant women, whose body is already running warmer
• Patients on diuretics (water pills) for blood pressure — they dehydrate faster
• People with diabetes, where dehydration can spike sugar dangerously
• Outdoor workers — security guards, delivery riders, vendors, masons — who often skip water because the toilet break is inconvenient

Prevention is not complicated, but it has to be consistent

There is no clever trick here. The protection comes from doing small things repeatedly through the day:

• Hydration schedule: drink 200–250 ml of water every hour you are awake during peak summer, not only when thirsty. By the time you feel thirsty, you are already 1–2% dehydrated.
• Add electrolytes: plain water alone is not enough if you sweat heavily. Use one ORS sachet in a litre of water, or homemade nimbu pani with half a teaspoon of salt and one teaspoon of sugar. Coconut water and chaas are excellent natural options.
• Avoid the 12–4 PM window: schedule outdoor errands before 11 AM or after 5 PM.
• Dress for the heat: loose, light-coloured cotton. A wet handkerchief on the back of the neck under a cap works surprisingly well for outdoor workers.
• Skip the wrong drinks: alcohol, very sweet sodas, and excess coffee actually pull water out of your body.
• Eat lighter, more often: heavy fried meals divert blood to the gut and away from cooling.

Which blood tests should you do — and when

Many people ask whether they need a routine summer check-up. My answer depends on who you are. For background on test preparation, see our complete fasting blood test guide, and to understand why sample handling affects accuracy, read why direct-to-lab testing gives more accurate results.

One last thing

Heat stroke kills more people in India every year than most of us realise — and almost every case is preventable. The body gives you signals. The job is to listen early, not late. If you are reading this for an elderly parent or a worker in your home, please share it with them today, not tomorrow.