What is a Fever?

What is a Fever?

Woman with fever lying in bed checking thermometer

A fever is a body temperature that is higher than average. It’s typically a sign of an immune system’s natural response to an infection or a virus.

A person’s average normal body temperature is 98.6° Fahrenheit. For adults, a fever is when your body temperature is above 100.4°F. For children, a fever is a body temperature higher than 99.5°F (taken orally), 99°F (taken under the arm), or 100.4°F (taken rectally).

Fevers show that your body is working to fight off a virus or infection—a normal and healthy response. Most fevers can be treated at home, but there are certain situations where a fever can be cause for concern.

Types of Fevers


A fever is traditionally categorized by how high your temperature is and how long it lasts. There are five general types of fever, including:

  • Intermittent fever - This type of fever fluctuates between normal body temperature and higher-than-normal levels through the day
  • Remittent fever - Like intermittent fever, this fever fluctuates throughout the day, but never falls all the way back to a baseline normal temperature
  • Hectic fever - With hectic fever, temperatures swing severely throughout the day, with a difference of at least 1.4 degrees Celsius between the lowest and highest measurements. A remittent or intermittent fever can be considered hectic.  
  • Continuous (or sustained) fever - Continuous fever is a steady, prolonged fever, with no change or slight fluctuations throughout the day
  • Relapsing fever - This type is an intermittent fever that spikes again after days or weeks of having a normal body temperature

Fevers can be considered mild, moderate, or high. What constitutes a fever temperature-wise varies between adults, children 11 and younger, kids 12 and older.

Fevers in infants (0 to 3 months) and sustained fevers in children, especially those under 2, warrant a call to your pediatrician.

Signs & Symptoms of Fevers


Fever symptoms vary depending on the type of fever, the temperature, and the cause. A fever in adults can produce different symptoms than children may have. 

Beyond an elevated body temperature, fever symptoms can include:

  • Chills or shivering
  • Sweating
  • Headaches
  • Body aches
  • Fatigue
  • Feeling dehydrated
  • Loss of appetite
  • Hot skin to the touch
  • Flushed complexion

A primary care doctor or your child’s general pediatrician can help address these symptoms, locate the cause, and recommend a specialist or emergency care when necessary.

Contact your pediatric doctor if your baby is under 3 months and develops a fever.

Conditions with fever as a symptom

A fever can be an indicator of many kinds of health issues, ranging from mild infections to severe diseases. Conditions that can have fever as a symptom include:

When to see a doctor

Fevers are common and typically don’t require medical attention. They are a sign of a health issue, however, so it’s important to pay attention to your symptoms and know when to get help.

If your child has a fever, contact a physician if the following criteria applies or these symptoms appear:

  • Your baby is younger than three months old
  • A fever lasts longer than three days
  • Your child is confused, listless, or has trouble making eye contact
  • Your child vomits repeatedly
  • Has ear pain or tugs on their ear
  • Develops a fever after being left in a hot car
  • Has a fever-related seizure

Seek medical attention for an adult fever right away if accompanied by the following symptoms:  

  • Stiff neck
  • Irritability or confusion
  • Seizure
  • Severe headache
  • Dehydration (no tears, less urine, sunken eyes)
  • Severe light sensitivity. (Photophobia)
  • A rash
  • Pain when urinating
  • Abdominal pain
  • Trouble breathing
  • Vomiting
  • A fever above 103°F lasting more than two hours after taking fever-reducing medicine

Any adult fever above 105°F that doesn’t respond to home medication could be life-threatening. Call 911 immediately. 

What Causes a Fever?


Your body’s temperature is balanced by the area of the brain called the hypothalamus—your own interior thermostat. The hypothalamus makes temperature adjustments when the body encounters certain conditions, occasionally resulting in an elevated body temperature.

Fever causes can include:

  • Viral infection
  • Bacterial infection
  • Immunization and vaccines
  • Medication side effects
  • Teething in babies (low-grade, lower than 102°)
  • Heat exhaustion
  • Sunburn



Most fevers subside on their own or with the help of fever-reducing remedies. But high, persistent fevers, or fevers that worsen over time, can result in brain damage or even death.

Febrile or fever seizures are convulsions in children that a fever spike can cause. Fever seizures are not the same as epileptic seizures, lasting for 1 to 3 minutes, and are generally not serious.



Anyone can develop a fever, but avoiding getting sick is the best way to prevent one. You can help prevent infections and other causes of fever by doing the following:

  • Wash your hands
  • Avoid sharing silverware, cups, and other dining materials
  • Avoid touching your face
  • Get vaccinated against infectious diseases, including the flu and COVID-19
  • Carry hand sanitizer/wipes with you
Get Care

Trust NewYork-Presbyterian for Fever Care

At NewYork-Presbyterian, we represent the best primary care options for adults and children. If you are experiencing high body temperatures or a prolonged fever, our expert doctors can evaluate your symptoms, help determine the cause, and discuss your treatment options.

In addition to our top-notch primary care physicians, NewYork-Presbyterian offers same-day appointments for critical needs and easy scheduling with early, late, and weekend hours. We accept most insurances, offer a user-friendly patient portal, and provide referrals to world-renowned specialists.