5 crucial facts about heat-related illnesses
Medically reviewed by Dr. Betsy Koickel, MD on July 1st, 2025.
Heat-related illnesses are the most dangerous weather-related health conditions during the summer months, with heat-related deaths peaking in July and August.
Without rapid intervention, heat exhaustion can progress to heatstroke, a potentially fatal condition that leads to hundreds of deaths in the U.S. each year. Each year, heat waves result in more fatalities in the U.S. than tornadoes, earthquakes, floods and hurricanes combined.
Here are the facts about heat-related illness, including risk factors, signs and symptoms, prevention tips and what to do if you’re experiencing heat-related illness.
Heat-related illnesses range from mild to life-threatening
There are varying degrees of heat-related illness, and it can manifest in people differently. The most common heat-related illnesses include:
- Heat rash, also called prickly heat, develops when your sweat ducts are blocked, trapping sweat under the skin and causing irritation.
- Heat cramps are muscle pains or spasms in the legs, arms or abdomen caused by heavy sweating and loss of salts during intense activity.
- Heat syncope is dizziness or fainting after prolonged standing or sudden rising from another position in the heat, often due to dehydration.
- Heat exhaustion occurs when your body loses too much water and salt. It can develop after a long period of being in high temperatures and not drinking enough fluids.
- Heat stroke is a life-threatening condition that occurs when your body’s temperature regulation system fails, rising above 104°F (40°C).
While conditions like heat rash are rarely dangerous, if more significant heat-related illnesses aren’t treated immediately, they can result in organ injury and death.
There are several risk factors for heat-related illnesses
Heat illnesses are most likely to occur in July and August when temperatures in the U.S. reach their peak.
The very young, the elderly and people with chronic health conditions are most susceptible to heat-related medical conditions since their bodies may not be able to regulate their internal temperature properly.
Effective heat illness prevention is possible
Tragically, between 600-700 people die every year from heat-related illnesses in the U.S. The good news is that these deaths are entirely preventable.
Know the heat index as part of your heat illness prevention plan
Knowing the temperature forecast for a hot day isn’t as helpful as knowing the heat index. Most weather apps and websites include heat index information.
A heat index is calculated by factoring in the relative humidity with the actual air temperature, and it’s a more accurate indicator of how your body perceives the heat. For instance, if the air temperature is 96 degrees F and the relative humidity is 65%, your body will experience a heat index of 121 degrees F.
Drink plenty of fluids to prevent heat illness
Your body needs more fluids than usual on hot days because of water loss from sweating, and because water evaporates faster off hot skin.
Staying hydrated is one of the most effective ways to avoid a heat-related illness. Drink plenty of water and avoid excessive amounts of caffeine and alcohol, since these are diuretics that cause you to urinate more. Eating hydrating foods, such as fruits and vegetables, can help as well.
It is important to start drinking before you feel thirsty because thirst is a symptom of early dehydration. Pro-tip: Keep a water bottle handy at all times so drinking water becomes a habit and doesn’t feel like a task.
There’s no specific recommendation for the amount of water you “should” drink because everyone’s body and hydration needs are different. However, if you’re urinating at least every 4 hours and your urine is a pale yellow color, you’re likely drinking enough to avoid early dehydration.
Wear appropriate clothing for heat illness prevention
Your skin is your largest organ, which means it’s a key player in keeping your body temperature within a safe range. In hot weather, make sure to wear lightweight, loose-fitting clothing that allows your skin to sweat and cool properly.
Also, if you wear a hat, make sure it allows for good ventilation since 50% of body heat is emitted from the scalp and face.
Time outdoor activities carefully to prevent heat illness
Heat-related illnesses can be prevented by avoiding the sun during peak temperatures (usually 12 p.m. - 3 p.m.) and properly cooling your home during those hours.
If your job or hobby requires frequent time in the heat, be prepared with plenty of water, sun-protective clothing and a hat. Find areas where you can escape the heat, like a car, a shade tree or a pavilion.
Acclimatization can also help, which is the process by which the body gradually adapts to higher temperatures. It typically takes 1-2 weeks of regular and gradual exposure to hot conditions.
It’s important to know the signs and symptoms of heat-related illnesses
Heat illness symptoms can vary depending on the condition:
- Heat rash: Red clusters of pimples or small blisters and uncomfortable itchiness that generally affect the neck, chest, groin or elbow creases.
- Heat cramps: Cramping of your muscles, excessive sweating, fatigue and thirst.
- Heat syncope: Lightheadedness, fainting, pale or sweaty skin and a weak pulse.
- Heat exhaustion: Sweating, skin that feels cold, pale, or clammy, a rapid faint pulse, nausea or vomiting, cramps, dizziness, headache and fainting.
- Heat stroke: Hot, red, dry, or damp skin, a strong and rapid heartbeat, confusion or trouble speaking and understanding others.
In extreme cases, heat-related illnesses can cause confusion, seizures and loss of consciousness.
Heat-related illnesses require urgent medical attention.
While many cases of heat-related illnesses can be prevented if you take the recommended precautions, it’s also important to remember that if you or someone you know does develop heat illness signs, it’s imperative to seek immediate medical attention.
Most cases of heat-related illnesses can be reversed with IV hydration and rapid core cooling if patients receive medical attention soon enough.
We're here to help
These are all interesting facts about heat, and we’re equipped to help with heat-related medical conditions. We offer IV hydration and a range of other services to treat illnesses and injuries. We are open 7 days a week. Walk in or save your spot online to get started.
FAQs
Here are some questions and facts about heat:
What is the main difference between heat exhaustion and heat stroke?
Heat exhaustion causes heavy sweating, weakness and dizziness, while heat stroke is more severe and includes confusion, no sweating and a high body temperature.
How quickly can heat-related illness develop?
Heat illness can develop within minutes during intense heat, especially with high humidity or physical activity.
What is an interesting fact about heat and how it affects us?
An interesting fact: the body can lose its ability to sweat as heat illness worsens, making it harder to cool down.
When should I visit urgent care for a heat illness?
Visit urgent care if symptoms of heat exhaustion don’t improve within an hour or if there are signs of heat stroke, like confusion or fainting.
What are some key heat illness prevention tips for children?
Keep kids hydrated, dress them in light clothing, avoid outdoor play during peak heat and never leave them in a parked car.
References:
