What Causes Hyperthermia?

Hyperthermia is caused by the body’s inability to regulate its temperature in the presence of high environmental heat. Hyperthermia can be severe and dangerous in the case of heat stroke.

Hyperthermia is a high body temperature. Hyperthermia also refers to heat-related illnesses, such as heat rash, sunburn, heat cramps, heat exhaustion, and heat stroke. 

• Heat rash (also called sweat rash, prickly heat, or miliaria) describes red bumps that form when sweat ducts become blocked. 
• Sunburn is a type of skin burn and inflammation caused by overexposure to ultraviolet (UV) radiation from the sun or a UV/tanning lamp.
• Heat cramps are brief but painful muscle cramps that occur during or after exercise or work in a hot environment.
• Heat exhaustion often occurs when people work or play in a hot, humid environment and body fluids are lost through sweating, causing the body to overheat and become dehydrated. Body temperature may be elevated, but usually not above 104° F (40° C).
• Heat stroke (also called sun stroke) is the most severe form of heat-related illness. It is a life-threatening medical emergency that occurs when the body's cooling system stops working and the body’s core temperature increases to a point at which brain damage or damage to internal organs can occur (105° F [40.5° C] or greater).

This article focuses on hyperthermia that refers to heat-related illness, however, hyperthermia is also a type of cancer treatment in which body tissue is exposed to high temperatures (up to 113°F) to damage and kill cancer cells. 

Symptoms of heat rash include:

• A rash that most often appears on the head, neck, chest, or anywhere where the skin rubs together (such as an armpit)
• May look like a cluster of tiny bubbles under the skin or like a cluster of small pimples

Symptoms of sunburn include:

• Reddened skin that is hot to the touch 
• Skin pain
• Increased sensitivity to skin pressure and heat (e.g., hot water)
• Symptoms of serious sunburn include:
• Severe pain
• Skin swelling and blistering 
• Skin tanning later on due to skin damage
• Blisters
• Fever 

Symptoms of heat cramps are cramps that occur due to exercising in the heat and are: 

• Painful 
• Involuntary 
• Brief 
• Intermittent (they come and go) 
• Usually self-limited (they resolve on their own)

Symptoms of heat exhaustion include:

• Pale, cool, moist skin
• Profuse sweating
• Core temperature elevated to usually more than 100° F (37.7° C) but not above 104° F (40° C)
• Dizziness or lightheadedness

Symptoms of heat stroke include:

• Body temperature of 104°F (40°C) or higher
• Brain symptoms 
  • Confusion or problems thinking clearly
  • Seeing or hearing things that aren't real (hallucinations)
  • Trouble walking
  • Seizures
  • Fainting
  • Coma
• Fast breathing (hyperventilation)
• Fast heartbeat
• Skin redness (flushing) and warmth or heat
• Dry skin
• Vomiting or diarrhea
• Muscle cramps or weakness
• Headaches
• Absence of sweating due to dehydration
• Changes in blood pressure (may be high or low)

Hyperthermia (heat-related illness) is caused by heat exposure. 

Causes of heat rash include:

• Clogged sweat ducts that cause perspiration to become trapped under the skin
• Underdeveloped sweat ducts
• Hot, humid weather or tropical climates
• Intense physical activity that causes excessive sweating
• Overheating

Causes of sunburn include:

• Exposure to UVA and UVB rays from the sun or tanning beds

Causes of heat cramps include: 

• Sweating profusely 
• Most likely related to deficiencies in electrolyte including sodium, potassium, calcium, and magnesium 

Causes of heat exhaustion include: 

• Working or playing in a hot, humid environment a person has not adjusted to
• Excessive sweating that causes the body to lose fluids and salts (electrolytes)
• Inadequate fluid intake
• Wearing too many layers of clothing
• Alcohol consumption 
• Prolonged exposure to very hot and humid environments (more common in the elderly or people who have an underlying medical condition)

Causes of heat stroke include: 

• Not promptly treating heat exhaustion 
• Sweating no longer cools the body
• It can develop rapidly and can lead to death if not treated

Heat rash, sunburn, and heat cramps can be diagnosed with a patient history and physical examination. Additional testing is usually not needed unless there is a concern about dehydration or kidney damage. 

Heat stroke is a medical emergency and can be life-threatening. Seek medical care at a hospital’s emergency department right away if heat stroke is suspected or if the person has the following symptoms: 

• Inability to keep fluids down (vomiting) 
• Deterioration of mental status (confusion or delirium)
• Shortness of breath
• Chest pain
• Abdominal pain 

Other tests may be indicated to determine if heat stroke has affected other organs in in the body and may include:

• Blood tests
• Urine tests
• Chest X-ray
• Electrocardiogram (ECG) of the heart

Initial treatment for mild hyperthermia (heat-related illness) usually includes:

• Getting out of a hot, humid environment into a cool, dry environment 
• Cooling measures such as cool baths or clean cloth dipped in cold water and applied to areas with rash or sunburn
• Fluid intake
• Rest/stopping physical activity

Additional treatment for sunburn includes: 

• Nonsteroidal anti-inflammatory drugs (NSAIDs) such as aspirin, ibuprofen (Advil, Motrin), or naproxen (Aleve) for pain
  • Do not give aspirin to children because it can cause Reye’s syndrome, a rare but serious illness 
• Using a lotion or spray made for treating sunburn pain with a local anesthetic (numbing medication, e.g., Solarcaine, Dermoplast) or Aloe vera to soothe dry skin
• Avoid the sun until the redness and pain go away

Treatment for heat cramps involves the general remedies for hyperthermia and: 

• Drinking fluids with electrolytes such as sports drinks (for example, Gatorade or Powerade)
• Gently stretching muscles that are cramping

Treatment for heat exhaustion involves the general remedies for hyperthermia, however, it must be treated promptly. If symptoms last more than an hour despite home treatment, see a doctor immediately so heat exhaustion does not progress to heat stroke, which can be life-threatening.  

Heat stroke is a medical emergency. There is no home treatment for heat stroke. Seek medical attention immediately in a hospital’s emergency department. 

Heat stroke must be treated by a doctor; treatment involves cooling the body as soon as possible. Methods used to reduce a person’s body temperature may include: 

• Immersion techniques, such as placing the patient into an ice bath
• Evaporative techniques, such as using a fan to blow air on wet skin 
• Invasive cooling techniques, such as chilled intravenous (IV) fluids
• Additionally, ice packs applied to the body or cooling blankets may be used as adjuncts to the methods above

Treatment continues until the patient’s core body temperature is 101.3°-102.2° F (38.5°-39° C). 

Patients may be admitted to the hospital for observation and additional testing if needed.

Heat stroke can affect almost every organ system and can lead to complications such as:

• Brain damage
  • Cerebellar deficits
  • Dementia
  • Paralysis on one side of the body (hemiplegia)
  • Weakness of arms and legs (quadriparesis)
  • Personality changes
• Muscle damage
  • Breakdown of muscle tissue (rhabdomyolysis)
  • Compartment syndrome
• Acute kidney injury 
• Acute liver failure 
• Disseminated intravascular coagulation (DIC) (rare)
• Acute respiratory distress syndrome (ARDS)

When it is hot or humid, steps to prevent hyperthermia (heat-related illness) heat stroke include:

• Don’t exercise outdoors
• If you exercise outdoors, keep activity levels low and take frequent breaks
• Drink enough fluids, such as water or sports drinks
  • Avoid drinking large amounts in a short time, which can be harmful
• Exercise early in the day, before it gets too hot 
• Wear loose, lightweight clothing

Pay attention to symptoms of heat cramps or heat exhaustion and stop activity and cool down right away so symptoms do not progress to heat stroke, which is a medical emergency.