Hyperthermia vs. hypothermia

You may be familiar with the term hypothermia. This happens when your body’s temperature drops to dangerously low levels. The opposite can also occur. When your temperature climbs too high and threatens your health, it’s known as hyperthermia.

Hyperthermia is actually an umbrella term. It refers to several conditions that can occur when your body’s heat-regulation system can’t handle the heat in your environment.

You’re said to have severe hyperthermia if your body temperature is above 104°F (40°C). By comparison, a body temperature of 95°F (35°C) or lower is considered hypothermic. The average body temperature is 98.6°F (37°C).

Hyperthermia comes in many stages. Heat exhaustion, for example, is a common condition. But others, such as heat syncope, may be less familiar to you. The following is a list of hyperthermic conditions and other heat-related illnesses.

Heat stress

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:

  • dizziness
  • weakness
  • nausea
  • thirst
  • a headache

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

If long hours in high heat are causing you physical discomfort and psychological stress, you may be dealing with heat fatigue. People who aren’t used to extremely hot weather or hot working conditions are especially vulnerable to heat fatigue.

In addition to simply feeling hot, thirsty, and tired, you may have difficulty concentrating on your work. You may even lose coordination.

If you notice a strain on your physical and mental well-being, get out of the heat and cool down with fluids.

Slowly adjusting to working or exercising in a hot environment can help prevent future heat fatigue.

Heat syncope

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.

Learn more: What to expect during and after a syncopal episode »

Heat cramps

Heat cramps usually follow intense exertion or exercise in the heat. They’re usually the result of an electrolyte imbalance and are typically felt in the abdomen, leg, or arm muscles.

To help relieve heat cramps, rest in a cool place, and be sure to replenish the fluids and electrolytes that are lost when you sweat.

Heat edema

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.

Heat rash

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.

Learn more: Types of heat rash »

Heat exhaustion

This is one of the most serious stages of hyperthermia. Heat exhaustion occurs when your body can’t cool itself any more.

In addition to sweating profusely, you may experience:

  • dizziness
  • weakness
  • thirst
  • coordination issues
  • trouble concentrating
  • skin that’s cool and clammy
  • rapid pulse

This is the last stage before heat stroke occurs, so it’s important that you rest and rehydrate as soon as you feel symptoms developing.

If you don’t feel your symptoms improving, seek immediate medical attention.

Keep reading: Do you have heat stroke or heat exhaustion? Learn the signs »

Hyperthermia’s most serious stage is heat stroke. It can be fatal. Other heat-related illnesses can lead to heat stroke if they aren’t treated effectively and quickly.

Heat stroke can occur when your body temperature reaches above 104°F (40°C). Fainting is often the first sign.

Other signs and symptoms include:

  • irritability
  • confusion
  • coordination issues
  • flushed skin
  • reduced sweating
  • weak or rapid pulse

When these signs start to emerge, you should:

  • Try to get to a cool location, preferably one with air conditioning.
  • Drink water or electrolyte-filled sports drinks.
  • Take a cool bath or shower to help speed up your recovery.
  • Place ice bags under your arms and around your groin area.

If your symptoms don’t improve when you try cooling off and rehydrating, or you see someone who appears to be having a heat stroke, call your local emergency services immediately.

People who work in very hot environments or are exposed to high heat during the course of the job are at high risk for hyperthermia.

Construction workers, farmers, and others who put in long hours outside in the heat should take precautions against hyperthermia. The same is true for firefighters and people who work around large ovens or in indoor spaces that are poorly air-conditioned.

Certain health conditions can also put you at higher risk for hyperthermia. Certain heart and blood pressure medications, such as diuretics, can reduce your ability to cool down through sweat. If you’re on a low-sodium diet to help manage high blood pressure, you may be quicker to develop hyperthermia.

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.

Your body’s temperature is regulated by a part of the brain called the hypothalamus. It normally keeps your temperature at around 98.6°F (37°C), with slight variations throughout the day and night.

If your body senses an infection of a virus or bacteria, the hypothalamus may reset your body’s “thermostat” to make your body a hotter, less hospitable host for those infectious agents. In this case, fever occurs as part of the immune system reaction. As the infection disappears, your hypothalamus should reset your temperature back to its normal levels.

With hyperthermia from heat stroke, however, the body is responding to changes in your environment. The body’s natural cooling mechanisms, such as sweating, aren’t enough to overcome the heat of your surroundings. Your temperature climbs in response, causing you to experience some of the symptoms previously described.

Some over-the-counter medications, such as acetaminophen (Tylenol), can help bring down a fever. However, they would be ineffective in treating hyperthermia. Only a change in environment, rehydration, and external cooling efforts (such as cool water or ice packs on the skin) can reverse hyperthermia.

The first step in preventing hyperthermia 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.

Learn more about heat emergencies »