You may need to get plenty of rest and drink fluids to help your body heal. But if you have a high or long-lasting fever longer than 3 days, you may need urgent medical care.

A fever is a common side effect of illness like the flu. It happens when there is a temporary rise in body temperature. A fever is usually a sign that your immune system is busy fighting an infection or other illness.

In babies and toddlers even a slight fever may be a sign of a serious illness. In adults a fever is not usually serious or life-threatening.

However, sometimes a fever in adults can be a warning signal that something is not right. A high or persistent fever might be a sign of a serious health condition.

A fever is normally a short-term rise in temperature that helps your body get rid of illness. A fever begins when your immune system makes more white blood cells to fight an infection. The increase in white blood cells triggers your brain to heat your body up.

This causes a fever. In response, your body tries to cool itself off by tightening up on blood flow to your skin and contracting muscles. This makes you shiver and may cause muscle aches.

Your normal body temperature ranges from 97°F to 99°F (36.1°C to 37.2°C). You may have a fever if your temperature rises above this.

Adults typically have a fever if their body temperature increases to 100.4°F (38°C). This is called a low grade fever. A high grade fever happens when your body temperature is 103°F (39.4°C) or above.

Most fevers usually go away by themselves after 1 to 3 days. A persistent or recurrent fever may last or keep coming back for up to 14 days.

A fever that lasts longer than normal may be serious even if it is only a slight fever. This is because a recurrent fever might be a sign of a more serious infection or health condition.

Common fever symptoms in adults include:

  • sweating
  • chills (shivering)
  • headaches
  • muscle pain
  • loss of appetite
  • fatigue
  • weakness

Call your doctor immediately if you have a high grade fever — when your temperature is 103°F (39.4°C) or higher. Get medical help if you have any kind of fever for more than three days. Let your doctor know if your symptoms get worse or if you have any new symptoms.

Serious symptoms

A fever may be a sign of serious illness if you have:

  • a severe headache
  • dizziness
  • sensitivity to bright light
  • stiff neck or neck pain
  • skin rash
  • difficulty breathing
  • frequent vomiting
  • dehydration
  • stomach pain
  • muscle cramps
  • confusion
  • seizures

Other signs that a fever may be serious are:

  • pain when urinating
  • not urinating enough
  • passing dark urine
  • passing urine that smells bad

If you have serious fever symptoms, let your doctor know if you have recently traveled to a different country or attended an event that had lot of people. This may help your doctor find out the cause.

Common causes of a fever in adults are:

  • viral infection (like the flu or a cold)
  • bacterial infection
  • fungal infection
  • food poisoning
  • heat exhaustion
  • serious sunburn
  • inflammation (from conditions like rheumatoid arthritis)
  • a tumor
  • blood clots

Some adults may have a higher risk of getting a fever. If you have a chronic health condition or have been treated for a severe illness, you may be more likely to get a serious fever.

Let your doctor know about any fever symptoms if you have:

Some medications and treatments can also lead to a serious fever, these include:

A fever is not normally harmful on its own. Most fevers go away within a few hours to days as your body defeats an infection.

Help yourself feel better with these at-home flu remedies:

  • stay hydrated by drinking plenty of fluids, such as:
    • water
    • juice
    • soup
    • broth
  • eat light foods that are easy on the stomach
  • rest
  • use a cool compress, like a damp towel
  • take a warm sponge bath
  • dress in light, comfortable clothing
  • turn down the temperature in your room

Over-the-counter medications can help ease your fever and symptoms, like headaches and muscle pain:

  • ibuprofen (Advil, Motrin)
  • acetaminophen (Tylenol)
  • naproxen (Aleve, Naprosyn)

You may need treatment from your doctor for more serious causes of a fever. The treatment depends on the cause. Your doctor may prescribe medications to treat serious infections:

A fever may be a sign of serious illness. A high fever can also cause serious side effects.

Emergency Symptoms

Get emergency medical attention by going to the ER or calling an ambulance if you have any of these symptoms:

  • seizure or convulsions
  • fainting or loss of consciousness
  • confusion
  • hallucinations
  • severe headache pain
  • stiff or painful neck
  • difficulty breathing
  • hives or a rash
  • swelling in any part of the body

A fever in adults is usually not harmful on its own. It is a sign that your body is dealing with an infection or other illness. In some cases a high or long-lasting fever can be a sign of a serious illness. You may need urgent medical treatment.

Do not ignore a fever. Get plenty of rest and fluids to help your body heal. See your doctor if you have a fever that lasts longer than 3 days or if you have other severe symptoms.

If you have a chronic condition or have been treated for a serious illness, let your doctor know if you have any kind of fever.