As the world marked the fifth Heat Action Day on Tuesday, health experts and climate organisations warned of a growing but often overlooked threat: indoor heat in homes, schools, workplaces and care facilities.
The International Federation of Red Cross and Red Crescent Societies (IFRC), which launched Heat Action Day in 2022, made “indoor heat” the theme of this year’s campaign, highlighting the dangers of poorly ventilated buildings and homes without cooling systems.
While public concern often focuses on outdoor temperatures, experts say indoor environments can pose equal or greater health risks, particularly in overcrowded or poorly ventilated spaces.
According to the IFRC, prolonged exposure to high indoor temperatures can cause dehydration, heat exhaustion and heat stroke, with risks worsening when temperatures remain high overnight.
Children, older adults and people with chronic illnesses are especially vulnerable, while low-income households and residents of informal settlements face disproportionate risks due to limited access to cooling.
A study released ahead of Heat Action Day 2026 by World Weather Attribution, Climate Central and the Red Cross found that 4 billion people—nearly half the global population—experienced at least 30 additional days of extreme heat because of human-caused climate change.
Researchers said climate change has made many heat events at least twice as likely compared to historical conditions.
Health experts warned that prolonged indoor heat can worsen respiratory illnesses, diabetes and dementia, while also disrupting sleep, reducing productivity and affecting students’ learning.
Bangladesh has experienced increasingly severe heatwaves in recent years. In April this year, a mild-to-moderate heatwave affected 27 districts, including Dhaka.
Chuadanga recorded the country’s highest temperature at 39.7°C for three consecutive days, while Rajshahi reached 40°C, classified as a severe heatwave by the Bangladesh Meteorological Department.
The department classifies heatwaves as mild at 36–37.9°C, moderate at 38–39.9°C, severe at 40–41.9°C and very severe above 42°C.
Climate experts warned that rising temperatures are increasing health risks for vulnerable communities, particularly children and older adults in low-income areas.
A separate report published Tuesday by the Red Cross Red Crescent Climate Centre warned that more intense heatwaves and rising cooling demand are likely to continue across South Asia.
Based on surveys of more than 2,000 people in Bangladesh and Nepal, the report found that extreme heat is severely affecting health, livelihoods and overall well-being.
Outdoor workers remain highly exposed to dangerous conditions, while many women reported struggling to balance income generation, household work and health protection during heatwaves.
One respondent from an informal settlement in Dhaka described living in a cramped tin-roofed home with limited cooling, saying family members often struggle to sleep due to extreme heat.
The survey found that nearly all respondents had experienced dangerous heat conditions, while many reported financial hardship linked to poor sleep, reduced productivity and declining earnings.
Researchers said heat awareness programmes significantly improve protective behaviour, but only 14% of respondents believed enough was being done to address extreme heat.
The report called for stronger adaptation measures, including shaded public spaces, cooling centres, water points and improved heat awareness campaigns.
Experts said housing materials, poor ventilation and urban heat island effects are major contributors to indoor heat, especially in densely populated informal settlements.
To reduce heat exposure, the IFRC’s #BeatTheHeat campaign recommends measures such as painting roofs white, improving ventilation and increasing shaded spaces.
Health experts also advised people to drink water regularly, wear lightweight clothing, avoid outdoor activity during peak afternoon heat and check on elderly or chronically ill neighbours during heatwaves.
UN Secretary-General António Guterres warned that developing El Niño conditions could intensify global heat impacts in the coming months.
“El Niño conditions will pour fuel on the fire of a warming world,” he said, urging faster climate action and stronger protection for vulnerable populations.
The World Meteorological Organization said there is an 80% likelihood that El Niño conditions will develop by August and continue through at least November.
IFRC Secretary General and CEO Jagan Chapagain said more than 500,000 people die annually from heat-related causes worldwide.
“Extreme heat is here, and it is deadly,” he said.
Experts warned that as temperatures continue to rise, indoor heat can no longer be ignored, particularly for millions living in densely populated and poorly ventilated homes.
