How High of a Fever Is Dangerous for Adults? Here’s When It’s Serious

how high of a fever is dangerous for adults

5% to 20% of the US population gets the flu every year, resulting in 31.4 million outpatient visits annually. Whether you have the flu, the coronavirus, or another illness, one of the early symptoms is often a high-grade fever.

How high of a fever is dangerous for adults? Keep reading to find out.

By knowing how to recognize the symptoms, you can visit a doctor for treatment as soon as possible. Otherwise, the cause of your fever might lead to bigger complications in the future.

Don’t wait to get the help you need. Instead, learn how to recognize dangerous fever levels with this guide. 

A Little About Fevers

A fever is an elevation in body temperature. Usually, a body temperature above 98.6 F is considered elevated. However, a fever isn’t considered significant until it reaches about 100.4 F.

How high of a fever is dangerous for adults? Another below 100.4 F is considered a low-grade fever. If you have a fever above 100.4 F, you need to see a doctor.

Otherwise, your fever could result in delirium or convulsions. 

Possible Causes

Dangerous fever levels occur when your immune system is attacking a foreign invader, including a:

  • Virus
  • Bacteria
  • Fungi
  • Drug
  • Toxin

These invaders are fever-producing substances called pyrogens that trigger your body’s immune response. Pyrogens tell your brain to increase your body temperature to fight off the infections. Common medical conditions associated with high-grade fevers include:

  • Intracranial hemorrhage
  • Thyroid storm
  • Serotonin syndrome
  • Sepsis
  • Kawasaki syndrome
  • Drug overdose

A fever is also a natural response to colds, flu, infections, and autoimmune disorders. 


You’ll likely notice different symptoms between a low-grade and high-grade fever.

For example, low-grade (pyrexia) fever symptoms include:

  • Chills
  • Sweats
  • Headaches
  • Thirst
  • Low appetite
  • Feeling hot
  • Achy or tired eyes

An early high-grade (hyperpyrexia) fever can cause:

  • Extreme sweating
  • Dizziness
  • Muscle cramps
  • Fatigue
  • Weakness
  • Nausea

As the fever progresses, you might experience:

  • Cool, moist, pale skin
  • Mold confusion
  • Vomiting
  • Decreased urine
  • Contracted pupils

When your fever hits above 106.1 F, it can lead to:

  • Extreme confusion
  • Weak, fast heartbeat
  • Dilated pupils
  • Seizures
  • Shallow, rapid breathing
  • Loss of consciousness
  • Hallucinations

If you’re wondering how high of a fever is dangerous for adults, a fever about 106.1 F is extremely dangerous. Seek medical attention immediately to prevent long-term consequences.


You don’t always need to treat a low-grade fever. Remember, fevers indicate your body is fighting off an infection.

If you start to develop fever-related symptoms, however, you might want to use over-the-counter medications. These can include acetaminophen or ibuprofen. Make sure to rest and drink plenty of water.

If you develop a high-grade fever, however, the fever won’t go away until the infection is gone. Depending on the specific pathogen, you’ll likely need medical treatment.

Visit your local urgent care center right away if you develop a high-grade fever.

How High of a Fever Is Dangerous for Adults?: Know When It’s Time to See a Medical Professional

To recap, how high of a fever is dangerous for adults? If it’s above 106.1 F, it’s time to visit a medical professional.

Don’t wait to receive treatment. Contact us or just walk in to discuss your options.