Health expert explains how extreme heat could shape the 2026 World Cup

As the 2026 FIFA World Cup kicks off, millions of fans from around the world are converging in the United States, Canada and Mexico to cheer their teams toward international glory. Alongside the excitement, sports medicine experts are watching another factor that could influence the tournament: extreme heat.

With all matches scheduled throughout June and July, heat and humidity will create challenging conditions for players, fans, coaches, staff and event personnel in and around stadiums. Ten of this year's 16 World Cup venues are considered at very high risk for extreme heat, and Miami's open-air stadium ranks as the tournament's hottest venue.

Eric Coris, MD, professor of Orthopedics and Sports Medicine and chair of the Department of Family Medicine at the USF Health Morsani College of Medicine, says the danger stems from the combination of heat, humidity, exertion, hydration status, acclimatization and access to cooling strategies.

An international expert in heat illness, concussions and dehydration in athletes, Dr. Coris has provided care for competitors at the highest level. He serves as head team physician for USF Athletic Medicine and team physician for the Tampa Bay Buccaneers, and previously held a similar role with the Ohio State Buckeyes.

Dr. Coris explains what extreme heat could mean for the World Cup, who is at greatest risk and what can be done to help protect players and fans.

Q - Why is heat an important issue for this World Cup?

A - Summer conditions can be challenging for any athlete or non-athlete, especially in hot and humid locations such as Florida, Texas and Mexico where matches are being played. The risk is higher for athletes, fans and staff arriving from cooler regions - including parts of Northern Europe or the Southern Hemisphere - where they may not yet be acclimatized to summer heat.

Heat is always a concern in sports, but the World Cup presents a unique challenge because of the intensity of play and the variety of climates involved. Soccer players generate tremendous metabolic heat during a match, especially during repeated running and sprinting. In hot and humid conditions, the body has a harder time releasing that heat.

Humidity is particularly important because it limits evaporation, one of the body's main cooling mechanisms during exercise. As surrounding temperature climbs above 68°F, the body depends almost entirely on sweat evaporation to shed heat. When the air is already saturated with moisture, that mechanism is severely limited.

The physiological stakes are significant. During vigorous exercise, the body generates heat 15 to 20 times faster than when it is at rest, enough to raise core temperature 1.8°F every five minutes without adequate cooling. On a humid July afternoon in Miami, there is very little margin for error.

Q - What impact can heat and humidity have on athletes?

A - The biggest risk is the lack of acclimatization to the environment, and the World Cup draws teams from every climate on Earth.

Heat illness exists on a spectrum. Understanding where on that spectrum an athlete sits and acting early is what separates a recoverable situation from a tragedy.

In milder cases, heat leads to decreased performance, dehydration, fatigue and heat cramps. In the most extreme cases, such as exertional heat stroke, the effects can be deadly if not recognized and treated urgently.

Q - What do teams do to prepare their athletes for extreme heat?

A - The most important thing they can do is acclimatize to the heat ahead of time. Ideally, teams arrive early enough in the host city to train in those conditions before match day.

The body adapts after repeated sessions in hot conditions. Adults typically need four to seven sessions lasting at least one hour to become meaningfully acclimatized. The changes that occur are significant and improve performance: increased sweat rate, expanded blood plasma volume, lower resting core temperature and reduced electrolyte loss in sweat.

For teams arriving from cooler climates, this window matters enormously. For example, a Northern European squad flying into Miami without a structured acclimatization protocol is capable of generating enormous heat loads, but lacks the adaptations to dissipate it. Such a situation would represent the highest-risk profile in elite sport.

Beyond acclimatization, elite programs use several additional strategies:

• Pre-cooling: ice vests and cold fluid ingestion in the 30 minutes before kickoff to lower starting core temperature
• Halftime cooling: cold water immersion tubs, cooling vests and ice towels during the break
• Cooling breaks: mandated by FIFA for the 2026 World Cup
• Individualized hydration plans: based on each athlete's measured sweat rate and sodium losses
• Environmental monitoring: on-site measurements of environmental heat, called Wet Bulb Globe Temperature, that account for heat, humidity and sun exposure together

Q - Are fans and others in attendance also at risk?

A - The soccer players participating in the World Cup are among the best-conditioned athletes in the world, and they have great opportunities to get adjusted to the heat - so while extreme temperatures will certainly affect them, their risk is comparatively lower than that of the general public.

For the rest of us, the danger is real and often underestimated. Non-athletes, older adults, children and people with underlying medical conditions face significantly higher risk in extreme heat. Those who are not acclimatized can get into trouble quickly. And unlike athletes, most fans have no medical team standing by.

Certain factors raise the risk considerably for anyone in attendance:

• Arriving from a cooler climate without heat exposure in the preceding weeks
• Obesity or low fitness levels, which create a higher metabolic heat load and make it harder to cool down
• Recent illness, especially anything involving fever, vomiting or diarrhea in the past week
• Medications including diuretics, antihistamines (common allergy pills), antidepressants, ADHD stimulants or beta-blockers - all of which impair heat dissipation
• Alcohol consumption, which accelerates dehydration and impairs judgment about symptoms
• Standing in direct sun for extended periods, as radiant heat from stadium surfaces adds significantly to the heat load

Anyone working or attending the World Cup should be alert, prepared and proactive. It is important to hydrate before, during and after the event. Find shade when possible. Know where medical stations are located. And look out for the people around you.

Q - What are the warning signs people should look for?

A - The most dangerous condition is exertional heat stroke, and the key warning sign is mental confusion. If someone becomes confused, disoriented or behaves unusually while exercising or active in the heat, it should be treated as heat stroke until proven otherwise. Do not wait. Do not assume they are just tired.

Cooling the body temperature is absolutely critical and cold-water immersion is needed immediately. Heat stroke is 100% treatable, but it needs to be treated right away. Every minute that core temperature remains elevated above 104.9°F increases the risk of organ damage and death.

Earlier warning signs, before heat stroke develops, provide an opportunity to intervene:

• Muscle cramps, particularly if severe or involving the abdomen, back or full body
• Dizziness, lightheadedness or feeling like you might faint
• Nausea or vomiting
• Headache that comes on during activity
• Unusual fatigue
• Skin that feels cold and clammy even in the heat
• "Chills" or goosebumps on the head or neck during exercise (a classic and underappreciated early sign)
• Stopping sweating in hot conditions, a serious warning that the cooling system is failing

Q - What should people remember if they are active outdoors this summer?

A - The preventive steps are straightforward: stay conditioned, get acclimatized and hydrate well. And see your doctor before you participate in a sport, because some people have pre-existing conditions that might increase their risk.

Hydration deserves special emphasis because it is the most impactful and modifiable factor. And most people get it wrong. You should begin activity well hydrated, continue hydrating during participation and rehydrate thoroughly afterward.

The average male athlete can sweat about 1.5 liters per hour, while the average female athlete can sweat about 1 liter per hour. That creates a significant fluid deficit that accumulates quickly, especially in multi-hour practices or events. Most people fall further and further behind as activity continues, and that is exactly where they run into trouble.

• Before activity: Drink about 16 ounces of water two hours before going out in the heat. Start every session already hydrated.
• During activity: Drink at least 8 ounces every 20 minutes. Do not wait until you are thirsty. Thirst lags well behind actual dehydration.
• After activity: Replace about 150% of the fluid lost. A practical rule is that for every pound of body weight lost during activity, drink 16-24 ounces of fluid within six hours. Combining carbohydrates with fluid replacement speeds recovery.

Finally, if someone around you collapses in the heat and shows signs of confusion or altered behavior, do not wait for emergency services to start cooling. Get them into cold water immediately. An ice bath up to the chest is ideal. If no tub is available, a tarp filled with ice and water can work too.

Heat stroke is survivable, but only if it is recognized and treated without delay.

To learn more about heat illness prevention and treatment, click here.