Hot Weather and Older Adults: Heat Illness, Dehydration, and Medication Safety

Hot weather is not only a concern for people exercising outdoors. For older adults, heat illness can also happen at home, especially in a warm living room, a poorly ventilated bedroom, or an afternoon when the air conditioner is not used.

The World Health Organization notes that high temperatures can increase the risk of heat exhaustion and heatstroke, and can worsen cardiovascular disease, respiratory disease, kidney disease, diabetes, and mental health conditions. Heatstroke is a medical emergency.[1] The U.S. CDC also explains that adults aged 65 and older are more vulnerable to heat because the body may adjust to temperature changes more slowly, chronic diseases are more common, and some medicines can affect sweating, hydration, or temperature regulation.[2][3]

In other words, heat risk in older adults is not just about feeling tired. Some people may not notice that they are overheating. Others may have heart, kidney, blood sugar, or medication factors that make it harder for the body to handle heat. Caregivers should watch for changes in alertness, appetite, urine amount, body temperature, skin condition, and unusual weakness or confusion.

Recent systematic review and meta-analysis evidence also supports this concern: heat and heatwaves increase mortality and morbidity risk in older populations, with higher risk seen in very old adults, women, people with comorbidities, and some climate regions.[9] This article therefore treats heat illness as part of older-adult care and chronic disease management, not only as a reminder to drink water.

Taiwan data show a clear seasonal pattern. According to Taiwan Health Promotion Administration open data on heat injury monitoring, there were 3,496 monitored heat-injury medical visits in 2025. The highest months were June, July, August, and September, with July reaching 683 visits. Adults aged 65 and older accounted for about 18.5% of the 2025 monitored visits.[11] This is surveillance data and does not cover every medical institution, so it should not be interpreted as the complete national number of visits. It is still useful for showing that heat injury increases clearly during Taiwan's summer.

Why Older Adults Are More Vulnerable To Heat

Older adults often have a reduced ability to regulate body temperature. Taiwan's Health Promotion Administration lists adults aged 65 and older, people with chronic diseases, outdoor workers, infants and young children, and people taking certain medicines as higher-risk groups for heat illness.[4]

Several factors often overlap in older adults:

This is why the same weather may feel only uncomfortable for a younger person but cause dizziness, weakness, poor appetite, confusion, or heatstroke in an older adult.

Warning Signs Of Heat Illness

Heat illness is not limited to fainting. Taiwan's Health Promotion Administration describes several heat-related conditions, including heat cramps, heat syncope, heat edema, heat exhaustion, and heatstroke.[6] Family members do not need to diagnose the exact category at home. The key is to notice warning signs early.

If an older adult develops the following symptoms, help them move to a cool or air-conditioned place, loosen clothing, begin cooling, and consider medical care:

• Marked fatigue, weakness, dizziness, or unsteady standing.
• Headache, nausea, vomiting, or clearly reduced appetite.
• Heavy sweating, or very little sweating despite heat.
• Hot, flushed, or dry skin.
• Fast heartbeat, shortness of breath, or chest tightness.
• Less urination or darker urine.
• Speaking, responding, or behaving differently than usual; confusion, unusual sleepiness, or difficulty waking.

Call emergency services or seek urgent medical care if there is confusion, seizure, loss of consciousness, very high body temperature, chest pain, breathing difficulty, or no improvement after moving to a cool place and starting cooling measures.

What Caregivers Can Check Every Day

The CDC recommends that caregivers proactively check whether older adults are drinking enough fluids, have access to a cool environment, know how to stay cool, and have symptoms of heat stress.[2] In a Taiwan home-care setting, this can become a practical daily checklist:

Many heat problems build up gradually. A poor night's sleep, reduced food intake, too little fluid, and a hot room can together lead to sudden weakness or confusion later in the day.

Making “Cool, Hydrate, Pay Attention” Practical

Taiwan's Health Promotion Administration uses three simple reminders for heat prevention: stay cool, replenish fluids, and pay attention to body changes.[7] These ideas are easy to remember, but they need to be made practical at home.

Cool: Indoor Cooling Matters

If air conditioning is available, use it during hot periods at a comfortable and affordable setting, and use a fan to circulate air. Taiwan's Health Promotion Administration suggests setting air conditioning around 26 to 27 degrees Celsius with a fan when appropriate.[8] WHO also notes that fans can help with cooling when used with air conditioning, but fans alone may not be enough in extreme heat.[5]

Taiwan summers are often hot, humid, and still. High humidity makes sweat evaporate less easily, reducing the body's ability to cool down. Caregivers should not only ask whether windows are open; they should actually feel whether the room is hot and stuffy.

• Avoid going out during the hottest part of the day when possible; if going out is necessary, use shade and sun protection.[7]
• Close curtains during strong sunlight.
• Choose loose, breathable, light-colored clothing.
• Use a cool towel on the neck, armpits, arms, or legs.
• Avoid long cooking sessions in a hot kitchen during very hot weather.
• If power is out after a typhoon or air conditioning is unavailable, move to a shaded and ventilated place and ask family, neighbors, or local community offices about temporary cooling options.

Hydrate: Do Not Wait Until Thirsty

Older adults may not say they are thirsty. Taiwan's Health Promotion Administration and the CDC both remind people to drink fluids during hot weather and not wait until thirst appears.[2][7]

However, hydration advice is not the same for everyone. If an older adult has heart failure, kidney disease, dialysis, low sodium, or clinician instructions to restrict fluids or salt, do not simply say “drink more water.” Ask a physician, nurse, or pharmacist how much fluid is appropriate in hot weather and what warning signs should trigger medical contact.

For general care, small amounts throughout the day may be easier: after waking, between meals, before and after going out, and after bathing. Avoid replacing water with sugary drinks, alcohol, or large amounts of caffeinated drinks.[7]

If dizziness, weakness, heavy sweating, or suspected heat exhaustion occurs, Taiwan's Health Promotion Administration recommends leaving the hot environment, starting cooling measures, and using cool water with a small amount of salt or an electrolyte drink when appropriate. Avoid drinking a large amount of ice water at once. If symptoms do not improve, seek medical care.[7]

Pay Attention: Medicines And Chronic Disease Can Change Risk

Some medicines require extra attention during hot weather. CDC clinical guidance notes that diuretics, medicines with anticholinergic effects, some psychiatric medicines, and ACE inhibitors or ARBs used with diuretics may increase risk during heat exposure.[3]

The most important point is this: do not stop or change medicines on your own. Diuretics, blood pressure medicines, heart medicines, psychiatric medicines, antihistamines, pain medicines, and laxatives should be reviewed by a physician or pharmacist when there are concerns.

The evidence is not equally strong for every medication group. A 2026 scoping review on medication and heat-related illness in older adults found that diuretics, ACE inhibitors, ARBs, anticholinergic medicines, and antipsychotics are commonly discussed in the literature, but interactions among medicines, comorbidities, and heat exposure still need more research.[10] This article therefore uses a conservative message: be aware of risk and check with healthcare professionals, rather than changing medicines independently.

• Could these medicines increase dehydration, low blood pressure, heat illness, or fall risk during hot weather?
• If the older adult cannot eat, vomits, has diarrhea, or urinates much less, when should we call the clinic or go to the emergency department?
• If there are fluid or salt restrictions, how should fluids be managed in summer?
• What blood pressure, blood sugar, weight, edema, or breathing changes should trigger contact with the care team?
• How should insulin, inhalers, refrigerated medicines, or medical devices be stored during heat or power outages?[3]

Who Needs Extra Attention?

• Adults aged 65 and older, especially those living alone, with limited mobility, or with dementia.[2]
• People with hypertension, heart disease, stroke history, diabetes, kidney disease, or chronic lung disease.[1][4]
• People taking diuretics, some blood pressure medicines, psychiatric medicines, antihistamines, or medicines that affect sweating or alertness.[3]
• People with recent diarrhea, vomiting, fever, poor appetite, or poor sleep.
• People living in top-floor rooms, metal-roof houses, poorly ventilated homes, or rooms that become hot during the day.
• Older adults who need to go out for shopping, work, religious activities, rehabilitation, or family care duties.

In Taiwan, heat, humidity, and poor ventilation often occur together. Older adults can develop heat illness even without direct sun exposure. During heat alerts, family members should call or visit proactively rather than waiting for the older adult to ask for help.

When To Seek Medical Care

Mild heat discomfort should improve after moving to a cool place, drinking appropriate fluids, loosening clothing, and cooling the body. Do not delay care in the following situations:

A practical rule for caregivers: if an older adult's mental status is different from usual, or symptoms do not improve with rest and cooling, do not push through. Heat illness and acute worsening of chronic disease can overlap and need clinical judgment.

A Summer Care Reminder For Families

Older adults may not clearly say they feel unwell. They may only say they are tired, have no appetite, or feel heavy-headed. In summer, those comments are worth checking.

1. Check the environment: Is the room hot? Is there air conditioning or a cooler space?
2. Check fluids: How much has the person drunk? Has urine amount or color changed?
3. Check alertness: Is the person unusually sleepy, confused, or slow to respond?
4. Check chronic conditions: Are blood pressure, blood sugar, breathing, edema, or body weight unusual?

Preventing heat illness is not only about staying indoors. It is about helping the body cool down, maintaining safe hydration, and noticing changes early. As summers become hotter, these small checks are becoming a practical part of caring for older adults.

Medical Disclaimer

This article is for general health education only and does not replace diagnosis or advice from a physician, pharmacist, nurse, or other healthcare professional. If you or an older family member has heart disease, kidney disease, diabetes, hypertension, dementia, psychiatric medicines, dialysis, fluid or salt restrictions, or symptoms such as altered consciousness, high body temperature, chest pain, breathing difficulty, reduced urination, or severe weakness, seek medical care promptly or call emergency services.

References

1. World Health Organization. Heat and health. 2026-07-31. https://www.who.int/news-room/fact-sheets/detail/climate-change-heat-and-health
2. Centers for Disease Control and Prevention. Heat and Older Adults (Aged 65+). 2024-06-25. https://www.cdc.gov/heat-health/risk-factors/heat-and-older-adults-aged-65.html
3. Centers for Disease Control and Prevention. Heat and Medications - Guidance for Clinicians. 2025-09-18. https://www.cdc.gov/heat-health/hcp/clinical-guidance/heat-and-medications-guidance-for-clinicians.html
4. Taiwan Health Promotion Administration. Heat illness prevention guidance. https://www.hpa.gov.tw/Pages/Detail.aspx?nodeid=577&pid=10748&sid=10745
5. World Health Organization. Heatwaves: how to stay cool. 2024-10-11. https://www.who.int/news-room/questions-and-answers/item/heatwaves-how-to-stay-cool
6. Taiwan Health Promotion Administration. Diagnosis and management of heat illness. https://www.hpa.gov.tw/Pages/Detail.aspx?nodeid=577&pid=10746
7. Taiwan Health Promotion Administration. Preventing heat illness with cool, hydrate, and pay attention. 2026-05-25. https://www.hpa.gov.tw/5020/20092/n
8. Taiwan Ministry of Health and Welfare. Hot weather and older-adult health reminder. 2025-08-22. https://www.mohw.gov.tw/cp-7175-83569-1.html
9. Günsche S, et al. Mortality, morbidity and healthcare costs of short-term high temperatures and heatwaves exposure in older populations: a global systematic review and meta-analysis. Environment International. 2026;208:110129. https://www.sciencedirect.com/science/article/pii/S0160412026000875
10. Bridgeman MB, et al. Recognizing and Mitigating the Effects of Medication on Heat-Related Illness in Older Adults: A Scoping Review. 2026. https://pmc.ncbi.nlm.nih.gov/articles/PMC13214780/
11. Taiwan Health Promotion Administration. Heat injury monitoring data, Government Open Data Platform, data through 2026-08-30, metadata updated 2026-08-31. https://data.gov.tw/dataset/157637