Guide to Heatwave And Effects
Stay safe and informed! This comprehensive guide explains what a heatwave is, details its severe health effects (heatstroke, exhaustion), and provides essential tips for preparation and survival. Learn how to keep cool and protect yourself.
Written by Dr. M L Ezhilarasan
Reviewed by Dr. Rohinipriyanka Pondugula MBBS
Last updated on 26th Oct, 2025
Introduction
Hotter, longer summers mean more people are feeling the serious effects of a heatwave—dehydration, heat exhaustion, and even life-threatening heat stroke. Beyond personal discomfort, heatwaves strain power grids, worsen air quality, and disrupt daily life. This guide translates science into practical steps you can use right away. You’ll learn what a heatwave is, how to recognize early warning signs, who’s most at risk, and exactly how to stay safe at home, work, and on the go. We’ll cover first aid, when to get medical help, how medications can interact with heat, and what to do during a power outage. You’ll also find checklists, data-backed tips, and unique strategies like creating a “cool room,” using body cooling zones, and planning around the heat index and wet-bulb temperature. If symptoms persist or you’re unsure what to do for yourself or a loved one, you can consult a doctor online with Apollo24|7 for further evaluation. Let’s dive into staying healthy and resilient—before, during, and after the next heatwave.
What Is a Heatwave? Definitions, Heat Index, and Wet-Bulb Temperature
A heatwave is a prolonged period of unusually hot weather relative to local climate norms. Many national services define it by several consecutive days above a certain temperature threshold. For example, the UK Met Office classifies a heatwave when daily maximum temperatures meet or exceed a region-specific threshold for at least three days [4]. Because “unusually hot” depends on where you live, a heatwave in a coastal city might look very different from one inland.
Why heat sometimes feels worse than the number on your thermometer:
• Heat index: The “feels like” temperature that combines air temperature and humidity. High humidity reduces sweat evaporation—the body’s main cooling method—making you much hotter at the same temperature. A heat index above 40°C (104°F) is dangerous for prolonged outdoor activity without shade and hydration.
• Wet-bulb temperature: A more technical metric indicating the lowest temperature achievable by evaporating water into the air. At a sustained wet-bulb of around 35°C, even a healthy person at rest in the shade can no longer cool themselves by sweating—survival becomes difficult without mechanical cooling. This is rare but becoming more plausible during intense heatwaves.
• Other environmental factors amplify heatwave effects:
• Nighttime heat: Warm nights prevent recovery and increase next-day risk.
• Sun exposure and radiant heat: Direct sun and heat radiating off roads and buildings raise body heat load.
• Air quality: Heatwaves often coincide with ozone formation and wildfire smoke, compounding respiratory stress.
In practice, monitor both the temperature and humidity or the heat index and follow local alerts. If the heat index is in the “danger” range, scale back activities, prioritize shade and fluids, and check on vulnerable people. For precise planning, many weather apps display heat index; some regions provide wet-bulb globe temperature (WBGT) for outdoor work and sports.
Consult a Top Urologist
Health Effects of a Heatwave—From Mild to Life-Threatening
Heat affects the body along a spectrum. Recognizing early symptoms is crucial to preventing progression.
• Heat cramps: Painful muscle spasms (often calves, arms, or abdomen) due to heavy sweating and electrolyte loss. Treat by resting in a cool place and drinking fluids with electrolytes (oral rehydration solution or sports drink).
• Heat exhaustion: Signs include heavy sweating, weakness, dizziness, nausea, headache, fainting, clammy skin, and rapid heartbeat. Body temperature may be normal or slightly elevated. Move to a cooler area, lie down, elevate legs, sip cool fluids, and apply cool cloths. Symptoms should improve within 30–60 minutes.
• Heat stroke (medical emergency): Body temperature typically ≥40°C (104°F) with hot skin (often dry), confusion, seizures, or loss of consciousness. Call emergency services immediately. Begin rapid cooling: move to shade or AC, remove excess clothing, apply ice packs to neck, armpits, and groin, and use cool water immersion if possible.
Beyond these classic illnesses, heatwaves strain vital organs:
• Heart and circulation: Heat causes blood vessels to dilate and the heart to pump harder, aggravating heart disease or low blood pressure.
• Kidneys: Dehydration and heat can concentrate the blood and reduce kidney perfusion, increasing the risk of kidney injury.
• Brain: Heat can impair attention, mood, and reaction time; in severe cases, it causes brain swelling and seizures.
• Skin: Heat rash and burns from hot surfaces are common.
Population-level effects can be severe. During Europe’s 2022 heatwave, researchers estimated more than 61,000 excess heat-related deaths across the continent [6]. In the U.S., hundreds to thousands of deaths are associated with extreme heat each year, making it one of the deadliest weather hazards. In South Asia, heatwaves regularly drive spikes in hospital visits and dehydration-related complications.
Unique insight: Heat amplifies existing risks. For example, mild diarrhea or vomiting becomes dangerous faster in a heatwave because dehydration accelerates. Likewise, even small amounts of alcohol or caffeine can tip you into dehydration when combined with high heat and humidity. Planning for extra fluids and electrolytes on hot days is crucial (long-tail: hydration and electrolytes in hot weather).
If symptoms do not improve after initial first aid, or if you experience recurrent dizziness, weakness, or palpitations over several days, consult a doctor online with Apollo24|7. After severe dehydration, your clinician may advise blood tests for electrolytes and kidney function; Apollo24|7 offers a convenient home collection for tests like sodium, potassium, creatinine, and HbA1c if you have diabetes.
Who Is Most at Risk During a Heatwave and Why?
Heat does not affect everyone equally. The following groups face a higher risk:
• Older adults: Reduced sweating, lower thirst sensation, and common chronic conditions (heart disease, diabetes) elevate risk.
• Infants and young children: Higher body surface area-to-mass ratio, immature thermoregulation, and dependence on caregivers.
• Pregnant people: Increased cardiovascular load and dehydration risk; severe heat exposure has been linked with higher rates of preterm birth in some studies. If you experience persistent dizziness, contractions, or decreased fetal movement in heat, seek prompt care.
• People with chronic illnesses: Heart disease, hypertension, kidney disease, lung disease, and mental health conditions.
• Those on certain medications: Diuretics, antihypertensives (e.g., ACE inhibitors, ARBs, beta blockers), anticholinergics, some antidepressants and antipsychotics, stimulants, and some antihistamines can impair thermoregulation or fluid balance. Discuss heat precautions with your clinician before peak summer.
• Outdoor workers and athletes: High metabolic heat production plus hot environments increases the risk of heat exhaustion and heat stroke.
• Urban residents without AC: The urban heat island effect can make cities several degrees hotter, especially at night, increasing cumulative heat load.
• People in poverty or social isolation: Limited access to cooling, transportation, or health information.
• Pets: Dogs and cats can overheat quickly; cars become deadly within minutes. Never leave pets or children in parked vehicles.
Why risk increases: Medications that reduce sweating or alter blood pressure can limit the body’s ability to dissipate heat. Low-sodium diets combined with diuretics can increase electrolyte imbalance during heavy sweating. Nighttime heat (no relief at night) compounds dehydration and fatigue, making the next day’s exposure more dangerous.
Staying Safe in a Heatwave—Hydration, Cooling, and Home Prep
Hydration and electrolytes:
• Drink regularly; don’t wait for thirst. A practical rule: pale yellow urine is a good sign of adequate hydration.
• Include electrolytes if you sweat heavily or work outdoors. Options: oral rehydration solutions (ORS), sports drinks diluted 1:1 with water, or homemade solutions (clean water + a pinch of salt + a little sugar and citrus for taste). People with heart or kidney disease should follow clinician's advice about fluid and salt.
• Limit alcohol and excess caffeine—they can worsen dehydration. If you drink, alternate each alcoholic beverage with water.
Clothing, shade, and sunscreen:
• Wear lightweight, loose, light-colored clothing; wide-brim hats; UV sunglasses.
• Use broad-spectrum sunscreen (SPF 30+), reapply every 2 hours.
• Create shade with umbrellas or canopies; portable shade is crucial for outdoor workers and families.
Home cooling and the “cool room”:
• Designate one room as your “cool room”: close curtains/blinds during the day, use reflective shades or foil-backed blackout curtains on sun-facing windows, seal gaps, and run a fan plus an AC unit or evaporative cooler if appropriate for your climate.
• Cross-ventilate in the evening if outdoor temperatures drop; shut windows and blinds in the morning.
• Use fans wisely: fans help when indoor temps are below ~35°C (95°F). Above that, fans can blow hot air unless combined with skin-wetting or an AC. For high humidity, a simple spray bottle to mist skin and a fan can improve evaporative cooling (long-tail: fans vs air conditioner during heatwave).
• Body cooling zones: cool wrists, neck, armpits, and groin with cool packs or damp cloths. A cool foot bath can also lower core temperature.
Urban heat and air quality:
• plan errands early in the morning or late evening. Use shaded routes and green spaces.
• Check the air quality index (AQI) during heatwaves. If ozone or smoke is high, reduce strenuous outdoor activity and consider a well-fitted mask for particulate pollution.
Food and sleep:
• Lighter, more frequent meals reduce metabolic heat. Prioritize hydrating foods like watermelon, cucumber, and yogurt.
• Optimize sleep in heat: cool shower before bed, breathable cotton sheets, fan near an open (safe) window, or ice packs wrapped in a towel placed near ankles/calves.
First Aid and When to Seek Care?
Recognize and act fast:
Heat cramps
What to do: Stop activity, move to shade or AC, gently stretch and massage the muscle, and drink fluids with electrolytes. Avoid activity for several hours to a day to prevent progression.
Heat exhaustion
• Symptoms: Heavy sweating, weakness, dizziness, nausea, headache, clammy skin, fainting.
• What to do: Move to a cooler place, lie down, elevate legs, sip cool fluids, apply cool compresses to neck, armpits, and groin. Most people improve within 30–60 minutes.
• Seek care if: Symptoms persist longer than an hour, worsen, or you have heart/kidney disease, are pregnant, or are an older adult.
Heat stroke (medical emergency)
• Symptoms: Body temp ≥40°C, hot skin (sometimes dry), confusion, agitation, slurred speech, seizures, or unconsciousness.
• What to do: Call emergency services immediately. Start rapid cooling: cool water immersion (best), cold wet cloths with fanning, or ice packs to neck, armpits, and groin until help arrives.
Medications and conditions
• People on diuretics, blood pressure meds, anticholinergics, or psychotropics may have atypical symptoms or deteriorate faster.
• If you have chronic conditions and feel unwell during a heatwave despite rest and fluids, consult a doctor online with Apollo24|7. If your condition does not improve after trying these methods, book a physical visit to a doctor with Apollo24|7.
Testing after severe dehydration
• If you’ve had prolonged vomiting, diarrhea, or signs of dehydration (dark urine, extreme thirst, little urination) during a heatwave, a clinician may recommend labs for electrolytes, kidney function, and blood glucose. Apollo24|7 offers a convenient home collection for tests like sodium, potassium, creatinine, and HbA1c (for people with diabetes).
Work, Travel, and Exercise—Practical Adjustments for Heatwave Days
Outdoor work
• Follow work-rest cycles. As temperature and humidity rise, shorten continuous work periods and increase rest in shade/AC. Many organizations use the Wet Bulb Globe Temperature (WBGT) to set schedules; if your employer does not, at least adjust based on heat index and signs of strain.
• Hydration plan: Small, frequent sips; 250–500 ml every 20–30 minutes in heavy heat. Include electrolytes if sweating heavily.
• Buddy system: Monitor each other for confusion, clumsiness, or slurred speech—possible early signs of heat stroke.
Commuting and travel
• Never leave children, older adults, or pets in parked cars, even for “a few minutes.” Cabin temperatures can soar by 10–20°C within minutes.
• Plan travel at cooler times. If using public transit without AC, carry water, a small fan, and a spray bottle.
• For motorcyclists and cyclists: Choose breathable protective gear, schedule rides early/late, and take more frequent cooling breaks (long-tail: travel and urban commuting during heatwave).
Exercise and sports
• Scale intensity based on heat index and humidity. Consider indoor training or water-based exercise during peak heat.
• Heat acclimatization: Gradually increase exercise duration and intensity over 1–2 weeks at the start of hot season—this improves your sweating efficiency and lowers heart rate and core temperature at given workloads.
• Cooling strategies: Pre-cool with an ice slush drink or cold towel; during exercise, use shaded routes; post-exercise, cool down longer and rehydrate with electrolytes (long-tail: workplace heat stress guidelines and rest breaks).
After the Heatwave—Recovery and Long-Term Adaptation
Recovery
• Rehydrate over 24–48 hours with water and electrolyte-rich fluids; include lightly salted foods if appropriate for your health conditions.
• Prioritize sleep: even one or two cooler nights make a difference in restoring cognitive function and mood.
• Watch for delayed symptoms: lingering fatigue, headaches, palpitations, dark urine, or reduced urination. If these persist beyond a day or two, consult a doctor online with Apollo24|7.
Home and community review
• Conduct a “heat audit”: Which rooms got the hottest? Which low-cost fixes could help (weather stripping, reflective window film, exterior shading, light-colored curtains)?
• Create or refresh a heat kit: ORS packets, reusable ice packs, spray bottles, battery-powered fan, backup power bank, list of nearby cooling centers.
• Neighborhood resilience: Plant shade trees where feasible, advocate for cooling centers, water refill stations, and shaded bus stops (long-tail: urban heat island effect solutions).
• Track alerts: Sign up for text/app heat alerts from your meteorological service.
Climate-ready planning
• Insulate and seal homes to keep heat out—good insulation reduces both winter heat loss and summer heat gain.
• Consider reflective roofs or lighter exterior paint for buildings in hot climates.
• Employers and schools: Establish heat safety policies, schedule adjustments, and access to cool spaces.
Consult a Top Urologist
Conclusion
Heatwaves are becoming more frequent and intense, but the effects don’t have to catch you off guard. Understanding how heat index and humidity amplify stress on the body, recognizing early symptoms, and taking quick action can prevent emergencies. Small, practical steps—like creating a cool room, carrying electrolytes, and planning your day around peak heat—make a big difference. If you or someone you care for is in a higher-risk group, set up check-ins and adjust medications or routines in consultation with your clinician. If symptoms persist beyond basic first aid or you feel unwell during or after a heatwave, consult a doctor online with Apollo24|7 for personalized advice; after significant dehydration, home collection for electrolytes and kidney function tests can speed recovery. Prepare today with a heat kit, reflective shades, and updated alert apps. Share this guide with friends, family, and neighbors—especially those who might not realize how quickly heat exhaustion can escalate. With the right knowledge and simple tools, you can stay safer, cooler, and more resilient through the next heatwave.
Consult a Top Urologist
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Consult a Top Urologist
Dr. Kunal Kumar Mehar
Urologist
10 Years • Mbbs, Ms, Mch
Bengaluru
Apollo Medical Center, Marathahalli, Bengaluru
Dr. Mohammed Rehan Khan
Urologist
8 Years • MBBS, MS (General Surgery), Mch (Urology)
Barasat
Diab-Eat-Ease, Barasat
Dr. N Naidu Chitikela
Urologist
7 Years • MS, MCh
Chinagadila
Apollo Hospitals Health City Unit, Chinagadila
(100+ Patients)
Dr. Ravishankar L S
Urologist
25 Years • MS, DNB (Gen. Surg.) DNB (Genitourinary Surg.)
Chennai
Apollo Hospitals Cancer Centre Nandanam, Chennai
Dr Anupam Sharma
Urologist
18 Years • MBBS, MS(Gen Surgery), DNB (Urology)
Delhi
Apollo Hospitals Indraprastha, Delhi
Consult a Top Urologist
Dr. Kunal Kumar Mehar
Urologist
10 Years • Mbbs, Ms, Mch
Bengaluru
Apollo Medical Center, Marathahalli, Bengaluru
Dr. Mohammed Rehan Khan
Urologist
8 Years • MBBS, MS (General Surgery), Mch (Urology)
Barasat
Diab-Eat-Ease, Barasat
Dr. N Naidu Chitikela
Urologist
7 Years • MS, MCh
Chinagadila
Apollo Hospitals Health City Unit, Chinagadila
(100+ Patients)
Dr. Ravishankar L S
Urologist
25 Years • MS, DNB (Gen. Surg.) DNB (Genitourinary Surg.)
Chennai
Apollo Hospitals Cancer Centre Nandanam, Chennai
Dr Anupam Sharma
Urologist
18 Years • MBBS, MS(Gen Surgery), DNB (Urology)
Delhi
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Frequently Asked Questions
1) What’s the difference between heat exhaustion and heat stroke?
Heat exhaustion causes heavy sweating, weakness, dizziness, and nausea; it improves with rest and cooling. Heat stroke is a medical emergency with very high body temperature (≥40°C), confusion, or unconsciousness—call emergency services immediately (long-tail: signs of heat exhaustion vs heat stroke).
2) How can I stay cool during a heat wave without AC?
Create a shaded “cool room,” use reflective window coverings, cross-ventilate at night, use fans with skin misting, cool wrists/neck with damp cloths, and hydrate with electrolytes if sweating heavily (long-tail: how to stay cool during a heat wave without AC).
3) Should I change my workouts during a heatwave?
Yes. Exercise early or late, lower intensity, add extra rest, and hydrate. Consider indoor or water-based exercise. Gradually acclimatize over 1–2 weeks at the start of hot season (long-tail: heat index vs temperature explained for workouts).
4) Which medications can increase heat risks?
Diuretics, certain blood pressure medicines, anticholinergics, stimulants, and some psychiatric medications can impair cooling or fluid balance. Ask your clinician about summer adjustments. If symptoms persist, consult a doctor online with Apollo24|7.
5) When should I seek medical care?
If heat exhaustion doesn’t improve within 30–60 minutes of cooling and hydration, if you’re pregnant or have chronic disease and feel unwell, or if there are signs of heat stroke. After severe dehydration, consider lab checks; Apollo24|7 offers home collections for electrolytes and kidney function.