Hyperthermia refers to a group of heat-related conditions characterized by an abnormally high body temperature. It is an umbrella term which refers to several conditions that can occur when your body’s heat-regulation system can’t handle the heat in your environment.
Hyperthermia differs from fever in that the body’s temperature set point remains unchanged. The opposite is hypothermia, which occurs when the temperature drops below that required to maintain normal metabolism.
In humans, core body temperature ranges from 95.9°F to 99.5°F during the day, or 35.5°C to 37.5°C. In contrast, people with some level of hyperthermia have a body temperature of more than 100.4°F (38°C).
It often occurs during physical exertion or exercise in a warm or humid environment. During exercise, blood pressure rises to deliver more oxygen to working tissues, increasing body temperature and the amount of work the body must do to maintain a stable temperature.
When combined with other factors, such as warm weather that also raises the body temperature and reduces its ability to release heat, it is unsurprising that exercise can increase the likelihood of overheating.
Though less common, hyperthermia can also take place while someone is resting, especially during extreme heat waves. Those on certain medications, diets, and with some medical conditions can also be affected by hyperthermia even when they are at rest.
Children and older adults are at increased risk as well. Many kids play hard in the hot outdoors without taking time to rest, cool off, and stay hydrated. Older adults tend to be less aware of temperatures changes, so they don’t often respond in time if their environment heats up. Older adults who live in a home without fans or air conditioning may also face hyperthermia in extremely hot weather.
General risk factors of hyperthermia include:
- Immune conditions
- Heart conditions
- Blood pressure or circulation conditions
- Lung, kidney, and liver conditions
- Dehydration, especially chronic dehydration
- Metabolic conditions
- Sweat gland or sweating conditions
- Excessive alcohol intake
- Being underweight
- Diuretic medications, usually for high blood pressure or conditions, such as glaucoma and edema
- Medications for the central nervous system, including antihistamines, antipsychotics, and beta-blockers
- A low sodium diet or low salt diet
- Illicit drug use, particularly synthetic marijuana
Types of hyperthermia and their associated symptoms
The symptoms of hyperthermia depend on the stage it has reached or how much the body is overheated. Symptoms of overheating may develop very quickly or over the course of hours or days.
In general terms, the symptoms of hyperthermia depends on the type that develops; here we will consider the types of hyperthermia together with the symptoms
If your body temperature starts to climb and you’re unable to cool yourself through sweating, you’re experiencing heat stress. Heat stress can lead to serious complications, such as heat exhaustion and heat stroke.
In addition to feeling uncomfortably hot, you may also experience:
If you’re feeling signs of heat stress, get to a cooler area and rest. Start drinking water or other fluids with electrolytes that will help restore hydration. Electrolytes are substances in the body, such as calcium, sodium, and potassium that keep you hydrated. They help regulate your heart rate, nerve function, and muscle health.
If your symptoms worsen, seek medical attention.
Heat fatigue and cramps
- Excessive sweating
- Flushed or red skin
- Muscle cramps, spasm, and pain
- Headache or mild light-headedness
Heat exhaustion, if left untreated, can lead to heat stroke, which is a life-threatening condition.
- Cold, pale, wet skin
- Extreme or heavy sweating
- Fast but weak pulse
- Nausea, vomiting, and diarrhea
- Muscle cramps
- Intense thirst
- Less frequent urination and dark urine
- Difficulty paying attention or concentrating
- Mild swelling of the feet and ankles or fingers and hands
- Temporarily fainting or losing consciousness
Syncope, also known as fainting, occurs when your blood pressure drops and blood flow to the brain is temporarily reduced.
It tends to happen if you’ve been exerting yourself in a hot environment. If you take a beta-blocker to lower your blood pressure, you’re at greater risk for heat syncope.
Fainting is often preceded by dizziness or lightheadedness. You may feel close to fainting, but if you relax and cool down quickly, you may prevent actually losing consciousness. Putting your legs up can help.
As with other heat-related illnesses, rehydrating is key. Any fluid will do, but water or electrolyte-filled sports drinks are best.
Heat edema can occur if you stand or sit for a long time in the heat and are not used to being in warmer temperatures. This can cause your hands, lower legs, or ankles to swell.
This swelling is from fluid buildup in your extremities. This is possibly related to a response involving the aldosterone-stimulated reabsorption of sodium into the blood through the kidneys.
Usually heat edema spontaneously subsides over time once you become used to the warm environment. Cooling down and putting your feet up will also help, as will staying hydrated with adequate water and electrolyte intake.
Sometimes, being active in the heat for prolonged periods of time can cause red pimple-like bumps to appear on the skin. This usually develops underneath clothing that has become soaked with sweat.
Heat rash typically disappears on its own after you cool down or change clothes.
However, infection is possible if the skin isn’t allowed to cool soon after the rash has appeared.
Without treatment, heat stroke can lead to dangerous complications, especially in young children, those whose immune system is compromised, and people over 65 years of age.
With heat stroke the body temperature is more than 103°F to 104°F, depending on a person’s normal, average body temperature.
Temperature and many of the other early signs of heat stroke are the same as those for heat exhaustion.
- Fast, strong pulse or very weak pulse
- Fast, deep breathing
- Reduced sweating
- Hot, red, wet, or dry skin
- Blurred vision
- Irritability or mood swings
- Lack of coordination
- Fainting or losing consciousness
- Organ failure
Hyperthermia is generally diagnosed by the combination of unexpectedly high body temperature and a history that supports hyperthermia instead of a fever. Most commonly this means that the elevated temperature has occurred in a hot, humid environment (heat stroke) or in someone taking a drug for which hyperthermia is a known side effect (drug-induced hyperthermia). The presence of signs and symptoms related to hyperthermia syndromes, such as extrapyramidal symptoms characteristic of neuroleptic malignant syndrome, and the absence of signs and symptoms more commonly related to infection-related fevers, are also considered in making the diagnosis.
If fever-reducing drugs lower the body temperature, even if the temperature does not return entirely to normal, then hyperthermia is excluded.
A person should immediately stop what they are doing and move to a cool, shaded place with good airflow if they suspect hyperthermia.
People should seek medical attention if heat cramps last longer than one hour after they have rested in a cool place.
Medical attention should also be sought for general symptoms that do not improve within 30 minutes of rest and care.
Additional tips for treating mild to moderate hyperthermia include:
- Sipping cool water or an electrolyte drink
- Loosening or removing excess clothing
- Lying down and trying to relax
- Taking a cool bath or shower
- Placing a cool, wet cloth on the forehead
- Running the wrists under cool water for 60 seconds
- Not resuming activity until symptoms have gone away
- Placing ice packs or compresses under the arms and groin
- Using a fan to cool the skin
How to prevent hyperthermia
The first step is recognizing the risks in working or playing in extremely hot conditions. Being in the heat means taking the following precautions:
- Take cool-down breaks in the shade or in an air-conditioned environment. If you don’t need to be outside in extreme heat, stay indoors.
- Stay well hydrated. Drink water or drinks containing electrolytes, such as Gatorade or Powerade, every 15 to 20 minutes when you’re active in the heat.
- Wear lightweight, light-colored clothing when outdoors.
- If your home isn’t well air-conditioned, consider spending time in an air-conditioned mall, library, or other cool public place during hot spells.