The global health body said on Wednesday that timely risk assessment, adequate preparation and effective on-site medical response could prevent or manage most heat-related illnesses that occur during large events.
According to the WHO, evidence from decades of mass gatherings shows that event organisers can significantly reduce the burden on hospitals and emergency services when appropriate medical systems are established at venues.
“A WHO evidence review covering studies published between 1980 and 2025 documented nearly 500,000 medical encounters at mass gatherings, including more than 22,000 heat-related illnesses. The review found that more than 90 per cent of patients can be treated at event venues when on-site medical systems are well organised, reducing pressure on local hospitals and ambulance services,” it said.
The new guidance comes amid increasing concern over the health effects of extreme heat and its implications for large gatherings, where thousands or even millions of people may be exposed to high temperatures at the same time.
Heat becomes an event-planning challenge
Dr Chikwe Ihekweazu, Executive Director of the WHO Health Emergencies Programme, said extreme heat should no longer be viewed solely as an environmental concern but as an issue that requires direct attention from event planners, governments and emergency-response authorities.
Ihekweazu said heat was becoming an increasing threat to health, safety and operational continuity during mass gatherings.
“Heat should be addressed not only as an environmental hazard but also as a core operational and governance challenge requiring consistent risk assessment, preparedness and response,” he said.
The WHO official said heat-related deaths had increased by an estimated 63 per cent since the 1990s, with an average of 546,000 deaths recorded annually between 2012 and 2021.
He warned that the characteristics of mass gatherings could intensify people's exposure to extreme heat and make it more difficult for vulnerable individuals to access immediate assistance.
“Mass gatherings can increase heat risks through prolonged outdoor exposure, dense crowds, limited access to safe water, travel-related stress and unfamiliarity with local climatic conditions. Increasing demands on health services during major events can further compound the risks associated with extreme heat and delay access to appropriate medical care,” he said.
Climate change increasing heat risks
According to Ihekweazu, the risks facing mass gatherings are being compounded by the broader increase in extreme heat linked to climate change.
He cited findings from the Intergovernmental Panel on Climate Change showing that hot extremes, including heatwaves, have become more frequent and intense across most land regions since the 1950s.
He added that projections indicate further increases in the frequency and intensity of extreme heat as global temperatures rise.
For event organisers, the implications extend beyond the health of individual attendees. Extreme heat can affect transportation, crowd movement, security operations, communications and the ability of medical teams to respond quickly to emergencies.
WHO recommends water, cooling facilities
The WHO said its new resources, titled Prevention and management of heat-related illness at mass gatherings, were developed from systematic reviews and lessons learned from mass gatherings around the world.
Ihekweazu said the recommendations include ensuring that attendees have easy access to safe drinking water and adequate toilet facilities, while also providing cooling infrastructure and considering changes to event schedules when temperatures are particularly high.
“The new resources, titled Prevention and management of heat-related illness at mass gatherings, are based on systematic reviews and lessons learned from mass gathering events worldwide. The guidance recommends accessible safe drinking water and toilets, cooling infrastructure, schedule adjustments and effective crowd-flow management to reduce heat-related health risks,” he said.
The guidance also calls for organisers to consider how people move through venues, particularly where large crowds could create conditions that increase exposure to heat or restrict access to water, shade and medical assistance.
Protection of workers and real-time monitoring
The WHO further recommended protecting workers involved in mass gatherings, noting that staff, security personnel, medical teams and other event workers can also face prolonged exposure to high temperatures.
Ihekweazu called for comprehensive workforce protection, clear public communication, real-time health surveillance and properly prepared medical teams stationed at event venues.
Such measures, he said, should form part of broader event preparedness rather than being treated as emergency measures introduced only after heat-related incidents occur.
The guidance takes what the WHO described as a whole-of-event approach, recognising that decisions made in areas such as venue design, transport, security, communications, water supply and sanitation can affect whether attendees are able to reach cooling areas and medical services.
Guidance covers entire event cycle
The WHO said the recommendations are intended to cover the full life cycle of an event, from planning and preparation through operations and emergency response.
“The guidance covers the full event cycle and is designed to complement national heat-health action plans, occupational health and safety requirements, emergency preparedness arrangements and clinical guidance,” Ihekweazu said.
The organisation urged governments, event organisers and other partners to incorporate heat-risk management into health planning and operational preparedness for mass gatherings.
With extreme heat becoming an increasingly important public-health challenge, the WHO said effective preparation could help protect attendees and workers while reducing the strain that heat-related emergencies place on hospitals, ambulance services and other local health systems.