Most people have a body temperature of about 98.6°F (37°C). Anything a degree above this is considered a fever. Fevers are often a sign that your body is fighting off some type of bacterial or viral infection. A viral fever is any fever that’s caused by an underlying viral illness.

A variety of viral infections can affect humans, from the common cold to the flu. A low-grade fever is a symptom of many viral infections. But some viral infections, such as dengue fever, can cause a higher fever.

Read on to learn more about viral fevers, including common symptoms and treatment options.

Viral fevers can range in temperature from 99°F to over 103°F (39°C), depending on the underlying virus.

If you have a viral fever, you might have some of these general symptoms:

  • chills
  • sweating
  • dehydration
  • headache
  • muscle aches and pains
  • a feeling of weakness
  • loss of appetite

These symptoms usually only last for a few days at most.

A viral fever is caused by infection with a virus. Viruses are very small infectious agents. They infect and multiply within the cells of your body. A fever is your body’s way of fighting off a virus. Many viruses are sensitive to shifts in temperature, so a sudden increase in your body temperature makes you less hospitable to viruses.

There are many ways that you can become infected with a virus, including:

  • Inhalation. If someone with a viral infection sneezes or coughs near you, you can breathe in droplets containing the virus. Examples of viral infections from inhalation include the flu or common cold.
  • Ingestion. Food and drinks can be contaminated with viruses. If you eat them, you can develop an infection. Examples of viral infections from ingestion include norovirus and enteroviruses.
  • Bites. Insects and other animals can carry viruses. If they bite you, you can develop an infection. Examples of viral infections that result from bites include dengue fever and rabies.
  • Bodily fluids. Exchanging bodily fluids with someone who has a viral infection can transfer the illness. Examples of this type of viral infection include hepatitis B and HIV.

Both viral and bacterial infections often cause similar symptoms. To diagnose a viral fever, a doctor will likely start by ruling out a bacterial infection. They can do this by considering your symptoms and medical history, as well as taking any samples to test for bacteria.

If you have a sore throat, for example, they might swab your throat to test for bacteria that causes strep throat. If the sample comes back negative, you likely have a viral infection.

They can also take a sample of blood or other bodily fluid to check for certain markers that might indicate a viral infection, such as your white blood cell count.

In most cases, viral fevers don’t require any specific treatment. Unlike bacterial infections, they don’t respond to antibiotics.

Instead, treatment usually focuses on providing relief from your symptoms. Common treatment methods include:

  • taking over-the-counter fever reducers, such as acetaminophen or ibuprofen, to reduce a fever and its symptoms
  • resting as much as possible
  • drinking plenty of fluids to stay hydrated and replenish fluids lost while sweating
  • taking antiviral medications, such as oseltamivir phosphate (Tamiflu), when applicable
  • sitting in a lukewarm bath to bring your body temperature down

In many cases, a viral fever isn’t anything to worry about. But if you have a fever that reaches 103°F (39°C) or higher, it’s best to call a doctor. You should also call a doctor if you have a baby with a rectal temperature of 100.4°F (38°C) or higher. Learn more about managing fevers in babies.

If you have a fever, keep an eye out for the following symptoms, which all indicate a need for medical treatment:

  • severe headache
  • difficulty breathing
  • chest pain
  • abdominal pains
  • frequent vomiting
  • a rash, especially if it quickly gets worse
  • a stiff neck, especially if you feel pain when bending it forward
  • confusion
  • convulsions or seizures

A viral fever refers to any fever that results from a viral infection, such as the flu or dengue fever. While most viral fevers resolve on their own within a day or two, some are more severe and require medical treatment. If your temperature starts reading 103°F (39°C) or higher, it’s time to call a doctor. Otherwise, try to get as much rest as possible and stay hydrated.