Guides

Extreme Heat in Hawaiʻi: The Health Risks We May Be Overlooking

How heat affects the heart, kidneys, and brain, why repeated exposure matters, and practical ways to protect your health.

Hawaiʻi has long been known for its comfortable climate. We rarely experience the triple-digit temperatures that make headlines on the mainland, and many of us are accustomed to warm afternoons and humid evenings.

But familiar conditions aren't necessarily harmless.


Heat exposure can do much more than make us uncomfortable. It can increase the workload on the heart, interfere with kidney function, impair concentration, and aggravate existing medical conditions. In some circumstances, it can contribute to serious illness or death without heatstroke ever being diagnosed.


Researchers are also investigating the longer-term consequences of repeated exposure, particularly when homes remain hot through the night and the body has little opportunity to recover.


For Hawaiʻi residents, understanding these risks is becoming increasingly important.



Sunlit Hawaiʻi urban street with asphalt roads, concrete sidewalks, buildings, and illustrative surface temperatures showing how paved areas absorb and retain heat.

1. Why Heat Is Becoming a Greater Health Concern in Hawaiʻi


In October 2026, Honolulu Civil Beat reported an increase in emergency department visits for heat-related illness across Hawaiʻi. According to Hawaiʻi Department of Health figures cited in the article, the number of reported visits between May and September was:


  • 2024: 126 emergency department visits
  • 2025: 155 emergency department visits
  • 2026: 182 emergency department visits


That's an increase of approximately 44% over two years. But these figures are not a count of everyone whose health was affected by heat. The reporting does not provide a breakdown of heat exhaustion versus heatstroke, and the Civil Beat article does not establish whether urgent-care encounters are included in the underlying figures.


What the numbers may be missing


Some people seek care at urgent-care clinics, primary care offices, or through telehealth. Others are assisted by emergency medical personnel without being taken to a hospital, or recover at home without receiving professional care. These events may not appear in emergency department counts.


Another, potentially more significant issue is that heat can aggravate a condition that is recorded under a different diagnosis. A person might seek emergency care for worsening heart failure, a heart attack, dehydration, or acute kidney injury. If a contribution from heat is not recognized or documented, the encounter may not be identified as heat-related.


The reported series covers only May through September, and represents encounters rather than necessarily unique patients. In addition, variation in diagnostic coding and participating facilities can affect surveillance data.


Reported heat-related emergency visits are not the same as the total number of people affected by heat. The number of missing cases cannot be calculated from the reported counts.


Why asphalt and concrete matter


Trees and other vegetation help cool neighborhoods through shade and evaporation. Roads, parking lots, roofs, and building surfaces absorb sunlight, become hot, and release stored heat later. This contributes to the urban heat island effect. Surface temperatures can be much higher than the surrounding air, but the two measures should not be confused.


A paved neighborhood with relatively little shade may be substantially hotter than a nearby vegetated area, even within the same community.


Humidity adds another challenge


Our bodies cool themselves partly through evaporation of sweat. When humidity is high, sweat evaporates more slowly, making it harder for the body to release heat. Air temperature alone therefore doesn't tell the full story. Humidity, direct sunlight, airflow, physical activity, clothing, and individual health all influence risk.


2. What Excessive Heat Does to the Body


The body regulates temperature by directing more blood toward the skin, adjusting circulation, and producing sweat. These processes are effective under many conditions, but prolonged heat exposure or dehydration can strain several organs at once.



Anatomical illustration showing how excessive heat affects the heart, kidneys, brain, and skin, including increased cardiovascular strain, dehydration, and changes in temperature regulation.

The heart and circulation


As more blood is directed toward the skin, the heart may beat faster to maintain circulation. Sweating can reduce blood volume, making this work more difficult. For someone with coronary artery disease, heart failure, or another cardiovascular condition, additional heat-related strain may increase the risk of complications.


The kidneys


The kidneys regulate fluid and electrolyte balance. Fluid loss and reduced circulation can impair kidney function, sometimes causing acute kidney injury. A person can experience kidney strain without the dramatic symptoms usually associated with heatstroke.


The brain


Excessive heat and dehydration can impair concentration, coordination, alertness, and judgment. Headache, dizziness, fatigue, and irritability may occur. Confusion, slurred speech, seizures, or loss of consciousness during heat exposure are emergency warning signs.


The skin and sweating response


Sweating helps the body lose heat when moisture evaporates from the skin. Humidity and poor airflow can reduce the effectiveness of this process. Heavy sweating also causes fluid and electrolyte losses.


3. Heat Can Contribute to Death Without Causing Heatstroke


A person doesn't have to develop heatstroke for excessive heat to contribute to a serious or potentially fatal medical event. Heat increases cardiovascular demands, while dehydration can reduce circulation and strain the kidneys. In people with existing illnesses, this added burden can help precipitate a crisis.


What death records reveal


In a CDC analysis of 10,527 heat-related deaths in the United States from 2004 through 2018, heat was recorded as the underlying cause in approximately 59% and as a contributing cause in about 41%. Cardiovascular diseases were prominent among the underlying causes when heat was a contributing factor.


National death records also identified 2,391 heat-related deaths in 2024. These recorded cases are not necessarily a complete measure of every death in which heat played a role.


What about Hawaiʻi?


The emergency department figures in Civil Beat do not establish how many Hawaiʻi residents died as a result of heat exposure. A current independently verified statewide heat-related death count has not been established for this Guide.


Researchers may estimate additional deaths attributable to hot weather using population-level statistics. Such estimates differ from counts based on death certificates and cannot determine with certainty what would have happened to a specific individual.


Heat can contribute to a fatal medical event even when heatstroke isn't listed as the primary cause.


4. Can the Effects of Heat Exposure Accumulate?


Prolonged or repeated heat exposure can create cumulative physiological stress, especially when daytime heat is followed by warm nights with inadequate cooling. This doesn't mean every hot day causes permanent injury. It means the body's effort to regulate temperature may continue over multiple days without sufficient opportunities for recovery.


What happens when nights stay hot?


A cooler nighttime environment allows the body to release heat and can reduce some of the stress experienced during the day. Hot rooms may interfere with rest and extend the period during which the cardiovascular and temperature-regulating systems are working harder.



Side-by-side illustration contrasting a hot daytime Hawaiʻi home with a cooler nighttime environment, showing heat-related strain on the heart, kidneys, and brain and the opportunity for recovery.

What about the kidneys?


Research involving agricultural workers and others performing strenuous activity in heat has identified repeated episodes of kidney strain and acute kidney injury. A 2025 review in Seminars in Nephrology discussed evidence linking environmental heat exposure to acute kidney injury and chronic kidney disease, while recognizing uncertainties about the mechanisms.


It is important not to assume that a person sitting in a warm home faces the same exposure as someone doing physically demanding outdoor work. Risks depend on intensity, duration, activity, hydration, medical conditions, and cooling opportunities.


Does the damage accumulate over years?


Long-term studies have linked greater heat exposure to adverse health outcomes, including cardiovascular and kidney outcomes. But the evidence does not establish that every heat exposure causes permanent accumulating damage.


The practical lesson is to reduce repeated excessive heat exposure rather than assume that the absence of heatstroke means there was no physiological strain.


5. Recognizing Heat Exhaustion and Heatstroke


Heat-related illness may develop gradually or rapidly. Recognizing symptoms and acting promptly can prevent dangerous delays in care.



Two-column comparison of heat exhaustion symptoms, including sweating, dizziness, and nausea, and heatstroke warning signs, including confusion, seizures, and loss of consciousness, with emergency instructions.

Heat exhaustion


Possible signs include heavy sweating, headache, nausea, dizziness, weakness, irritability, thirst, elevated body temperature, and reduced urination. Move the person to a cool environment, remove unnecessary clothing, and apply cool wet cloths or cold water to begin cooling.


If the person is fully alert and able to swallow safely, offer frequent sips of cool water. Stay with the person and seek medical evaluation. Escalate urgently if symptoms worsen, vomiting develops, or improvement doesn't occur promptly.


Heatstroke


Heatstroke is a medical emergency. Confusion, slurred speech, unusual behavior, seizures, fainting, or loss of consciousness during heat exposure are danger signs. The skin may be dry or sweaty. Do not delay action to obtain a temperature reading.


Call 911 immediately if heatstroke is suspected. Move the person to a cooler location and start rapid cooling with cold water, wet skin, cold packs, or cool-water immersion when safe and feasible. Stay with the person. Do not give drinks to someone with suspected heatstroke.



[DOWNLOAD 3 — HEAT, MEDICATIONS & YOUR HEALTH — PDF]


Filename: TWC_Heat_Medications_Personal_Risk_Worksheet.pdf


Link text: Download Heat, Medications & Your Health Worksheet (PDF)


Description: A printable worksheet to list medications, prepare questions for a doctor or pharmacist about heat sensitivity, and record individualized advice about hydration, medical conditions, medication storage, and warning signs.


PDF file: Download revised PDF #3


7. Practical Ways to Keep Your Home Cooler


Air conditioning is one of the most effective ways to reduce indoor heat exposure. Hawaiʻi's electricity costs, however, make frequent use difficult for some households. Lower-cost methods may reduce heat buildup or improve comfort, although they are not always substitutes for a cool indoor environment.



Hawaiʻi house with exterior window shading and illustrated home-cooling strategies, including blocking direct sunlight, improving airflow, and reducing indoor heat sources.

Block direct sunlight


Use curtains, shades, shutters, exterior awnings, or suitable reflective coverings. Exterior shading is especially valuable because it blocks solar energy before it enters through glass.


Ventilate at the right time


Open windows when outdoor air is cooler than the air inside and ventilation is safe. Opening windows during hotter periods can increase indoor heat. An indoor thermometer can help you judge conditions.


Know the limits of fans


Fans move air and can improve comfort and sweat evaporation, but do not lower the room's air temperature. CDC guidance cautions against relying on fans for cooling when indoor temperatures are 90°F or higher. Even below that temperature, a fan may not be adequate for a vulnerable person during prolonged heat.


Reduce indoor heat sources


Limit unnecessary use of ovens, stoves, clothes dryers, and other heat-producing appliances during the hottest periods. Turn off unneeded equipment when practical.


Cool the body directly


Cool showers, damp cloths, and wetting the skin can help reduce heat stress. Maintain suitable hydration, but follow individualized medical advice if you have heart or kidney disease, a fluid restriction, or other medical concerns.


Identify somewhere cooler to go


Plan ahead for an accessible, air-conditioned location such as a public library, shopping center, or community facility, checking its hours and accessibility before you need it.


[DOWNLOAD 2 — KEEP YOUR HOME COOLER — PDF]


Filename:  02_Keep_Your_Home_Cooler.pdf


Link text: Download Keep Your Home Cooler (PDF)


Description: A printable checklist covering window shading, airflow, fans, indoor heat sources, and ways to cool the body.


PDF file: Download PDF #2

8. Where Hawaiʻi Residents Can Find Assistance


The Hawaiʻi Home Energy Assistance Program (H-HEAP) helps eligible households with electric or gas bills. The Energy Credit program accepts applications during June. Energy Crisis Intervention is intended for qualifying energy emergencies, subject to program criteria and limits.


Applications are handled through the community action agencies serving each island. Eligibility, application deadlines, and available funding should be checked with the program because they can change.


Official resource: https://humanservices.hawaii.gov/bessd/liheap/


Residents can also call 2-1-1 for community-resource referrals. Utility-bill assistance is not automatically the same as financial assistance to purchase an air conditioner; ask what a particular program covers.


9. Create a Household Heat-Safety Plan


Identify the coolest room in your home and monitor indoor conditions. Know where you could go if your home becomes too hot. Keep needed drinking water, medications, and cooling supplies available, and plan for possible power outages.


If you take medications affecting fluid balance or temperature regulation, ask a healthcare professional for an individualized hot-weather plan. People using refrigerated medications or electrically powered medical equipment should plan for outages and transportation needs.


Arrange regular check-ins with older family members, neighbors, or people living alone during periods of excessive heat. Someone becoming confused may not recognize the danger or be able to ask for help.


A Final Thought


Heat safety is about more than preventing heatstroke. The body can experience significant stress from excessive temperatures without the dramatic symptoms usually associated with a heat emergency. People with existing medical conditions, limited access to cooling, or repeated exposure may face particularly serious consequences.


Understanding these risks doesn't mean avoiding all warm weather. It means recognizing when heat is creating unnecessary physiological strain and taking practical steps to reduce exposure, especially when days stay hot and the nights don't cool down.


References and Further Reading

  1. Honolulu Civil Beat, Twilight Greenaway. Hotter Than Ever: Hawaiʻi Preps Kūpuna For Extreme Heat. October 2026. https://www.civilbeat.org/2026/10/hotter-than-ever-hawaii-preps-kupuna-for-extreme-heat/
  2. World Health Organization. Heat and Health. https://www.who.int/news-room/fact-sheets/detail/climate-change-heat-and-health
  3. CDC. Heat and Your Health. https://www.cdc.gov/heat-health/
  4. CDC/NIOSH. Heat-Related Illnesses. https://www.cdc.gov/niosh/heat-stress/about/illnesses.html
  5. CDC. Heat and Medications: Guidance for Clinicians. https://www.cdc.gov/heat-health/hcp/clinical-guidance/heat-and-medications-guidance-for-clinicians.html
  6. Vaidyanathan A, et al. Heat-Related Deaths, United States, 2004–2018. MMWR, 2020. https://www.cdc.gov/mmwr/volumes/69/wr/mm6924a1.htm
  7. Hyndman KA, et al. High Environmental Heat Exposure Is a Risk Factor for Acute Kidney Injury and Chronic Kidney Disease. Seminars in Nephrology, 2025. https://pubmed.ncbi.nlm.nih.gov/40914669/
  8. U.S. Environmental Protection Agency. Reducing Urban Heat Islands. https://www.epa.gov/heatislands
  9. Hawaiʻi Department of Human Services. Hawaiʻi Home Energy Assistance Program. https://humanservices.hawaii.gov/bessd/liheap/

Educational material, not a substitute for personalized medical advice. Suspected heatstroke is an emergency: call 911.


Notes from Marsha


I hadn't realized that heat exposure could contribute to a heart attack, kidney injury, or even death without being identified as the primary cause. I was equally surprised by how much heat-related illness may be missing from the statistics we see.


The research on repeated exposure raises another concern. What happens when someone lives in a hot home day after day, with little opportunity for the body to recover overnight?


In Hawaiʻi, where many households lack air conditioning or can't afford to use it regularly, these are questions worth taking seriously. I hope this Guide helps readers recognize risks they may never have considered.

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