Normal body temperature is typically 98.6°F (37°C). However, slight fluctuations can occur throughout the day. For example, your body temperature is lowest in the early hours of the morning and highest in the late afternoon.

You’re considered to have a fever when your body temperature rises a few degrees above normal. This is typically defined as 100.4°F (38°C) or higher.

In some cases, your body temperature can rise greatly above its normal temperature due to things other than fever. This is referred to as hyperthermia.

When your body temperature exceeds 106°F (41.1°C) due to a fever, you’re considered to have hyperpyrexia.

Call your doctor if you or your child has a temperature of 103 degrees or higher. You should always seek emergency medical care for a fever if you’re experiencing the following symptoms:

  • temperature of 100.4°F (38°C) or higher in children under three months of age
  • irregular breathing
  • confusion or sleepiness
  • seizures or convulsions
  • severe headache
  • skin rash
  • persistent vomiting
  • severe diarrhea
  • abdominal pain
  • stiff neck
  • pain while urinating

In addition to a fever of 106°F (41.1°C) or higher, symptoms of hyperpyrexia can include:

  • increased or irregular heart rate
  • muscle spasms
  • rapid breathing
  • seizures
  • confusion or changes in mental state
  • loss of consciousness
  • coma

Hyperpyrexia is considered to be a medical emergency. If left untreated, organ damage and death can occur. Always seek immediate medical attention.

Infection

Various severe bacterial, viral, and parasitic infections can lead to hyperpyrexia.

Infections that can cause hyperpyrexia include but are not limited to:

  • S. pneumoniae, S. aureus, and H. influenzae bacterial infections
  • enterovirus and influenza A viral infections
  • malaria infection

Sepsis can also cause hyperpyrexia. Sepsis is a life-threatening complication from an infection. In sepsis, your body releases a variety of compounds into your bloodstream to help fight infection. This can sometimes produce a severe inflammatory response that can lead to organ damage and failure.

In order to diagnose an infectious cause of hyperpyrexia, your doctor will take a sample to test for the presence of microorganisms. Depending on the nature of the suspected infection, this sample could be a blood sample, urine sample, stool sample, or sputum sample. Your doctor can then identify the infectious agent using various culture or molecular methods.

Anesthesia

In rare circumstances, exposure to some anesthetic drugs can cause extremely high body temperature. This is referred to as malignant hyperthermia (sometimes called malignant hyperpyrexia).

Being prone to malignant hyperthermia is hereditary, which means that it can be passed from parent to child.

Malignant hyperthermia can be diagnosed by testing a sample of muscle tissue. If you have a relative who has malignant hyperpyrexia, you should consider being tested for the condition.

Other drugs

In addition to anesthesia drugs, use of certain prescription drugs can lead to conditions in which hyperpyrexia is a symptom.

An example of one such condition is serotonin syndrome. This potentially life-threatening condition can be caused by serotonergic drugs, such as selective serotonin reuptake inhibitors (SSRIs).

Another example is neuroleptic malignant syndrome, which can be caused by a reaction to antipsychotic drugs.

Additionally, some recreational drugs, such as MDMA (ecstasy), can cause hyperpyrexia.

Symptoms for these conditions typically develop shortly after exposure to the drug.

Your doctor will perform a physical exam and review your history of exposure to specific drugs to diagnose drug-related hyperpyrexia.

Heat stroke

Heat stroke is when your body overheats to dangerous levels. This can be caused by overexerting yourself in a hot environment. Additionally, people who have difficulty regulating their body temperature may develop heat stroke. This can include older adults, very young children, or individuals with chronic illnesses.

Your doctor will perform a physical examination to diagnose heat stroke. Since heat stroke and dehydration can stress the kidneys, they may also test your kidney function.

Thyroid storm

Thyroid storm is a rare condition that can occur when thyroid hormones are overproduced.

Early identification and treatment of thyroid storm are essential. Your doctor will use your medical history, symptoms, and lab tests to confirm thyroid storm.

In newborns

Hyperpyrexia is rare in infants. However, an infant with hyperpyrexia may be at risk for a serious bacterial infection.

Several studies have indicated an association with high fever and risk of serious bacterial infection in very young infants.

If your child is under 3 months old and has a fever of 100.4°F or higher, it’s very important that they receive prompt medical attention.

Treatment for hyperpyrexia involves addressing both the increase in body temperature and the condition that’s causing it.

Sponging or bathing in cool water can help lower your body temperature. Ice packs, blowing cool air, or spraying with cool water may also help. Additionally, any tight or extra clothing should be removed. When you have a fever, these measures may not work to bring down the temperature to normal, or even more than a degree or two.

You may also be given intravenous (IV) fluids as a supportive treatment and to help with dehydration.

If the hyperpyrexia is due to an infection, your doctor will identify the cause. They’ll then administer the proper drug therapy to treat it.

If you have malignant hyperthermia, your doctor or anesthesiologist will stop all anesthetic drugs and give you a drug called dantrolene. Going forward, you should always inform your doctor or anesthesiologist of your condition.

Drug-related hyperpyrexia is treated by discontinuing use of the drug, receiving supportive care, and managing symptoms such as rapid heart rate and increased blood pressure.

Conditions such as thyroid storm can be treated with antithyroid drugs.

Hyperpyrexia, or fever of 106°F or higher, is a medical emergency. If the fever is not lowered, organ damage and death can result.

In fact, if you’re experiencing a fever of 103°F or higher with other significant symptoms, it’s important that you seek immediate medical care.

Your doctor will work quickly to diagnose what’s causing your high fever. They’ll work to safely lower the fever before serious complications occur.