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Medical News Today: Can you have the flu without a fever?

The influenza virus causes the flu, which is a respiratory illness. Fever is a common symptom of the flu, but it is possible to have the flu without having a fever.

The flu is a very common illness that affects around 5 to 20 percent of the United States population each year. The virus is highly contagious and enters the body through the nose and mouth. Once in the body, the virus affects the respiratory system.

A fever is an abnormally high body temperature. It is a symptom of many conditions, not just the flu.

In this article, learn more about whether a person can have the flu without experiencing a fever.

Flu without a fever

Woman working at desk coughing into tissue with flu and no fever
Flu can cause symptoms such as coughing, muscle pain, and fatigue.

When fighting an influenza infection, the body may raise its temperature to make it difficult for the virus to replicate. This abnormal increase in body temperature is known as a fever.

A fever is part of the immune system’s response to an infection and is a typical flu symptom. However, it is possible for the flu to occur without a fever.

In mild cases of the flu, the body may be able to fight off the influenza virus without raising its temperature.

Body temperatures over 100.4°F (38°C) usually indicate a fever, but the exact temperature can vary.

Fevers in children can cause temperatures between 103°F to 105°F (39.4°C to 40.6°C), typically higher than in adults.

In addition to an increase in body temperature itself, a fever may also cause:

  • sweating
  • shivers
  • headaches
  • muscle aches
  • skin flushing
  • restlessness
  • weakness or dizziness

Common flu symptoms

The symptoms of flu occur rapidly after the infection takes place, as a result of the immune system fighting off the virus.

While the illness occurs in the upper respiratory tract, which includes the nose, throat, and bronchi of the lungs, symptoms can also affect the whole body.

In addition to a fever, common flu symptoms include

  • fatigue
  • a headache
  • muscle and joint pain
  • a sore throat and cough
  • a blocked or a runny nose
  • nausea, vomiting, or diarrhea (more common in children)

The symptoms of the flu can range from mild to severe. They often have a rapid onset and can become debilitating as the body’s immune system fights off the virus.

Flu vs. cold

Man sitting on train blowing nose into tissue
Flu is often more severe than a cold.

The common cold and the flu are both viral infections that affect the respiratory system. There are many similarities between their symptoms, but there are some key differences as well.

In general, the symptoms of flu are more severe and appear much quicker than with a cold. The flu is also more likely to involve a fever, which is rare with a cold.

Similarly, serious complications are more likely to occur with flu than with colds.

Complications are more likely to affect those with a weakened immune system, such as older adults, those with a severe chronic illness, and children.

Treatment

Most people can treat the flu at home by getting plenty of rest and drinking lots of clear fluids, such as water and herbal tea.

It is not always necessary to seek medical care or take medications to recover from the flu. During this period of rest, the immune system will fight off the infection.

Antiviral medications are also available for people with the flu. These medications can reduce symptoms and speed up recovery when taken within 1 or 2 days of the infection.

Two common antiviral medications for the flu are oseltamivir (Tamiflu) and peramivir (Rapivab).

These treatments can be useful for severe cases or for people who are at risk of complications. Those at risk of complications include:

  • young children
  • people aged 65 years or over
  • pregnant women
  • people with conditions that suppress the immune system, such as HIV
  • people taking immunosuppressants

When to see a doctor

A person experiencing chest or abdominal pain alongside a flue should see a doctor.
A person experiencing chest or abdominal pain alongside flu should see a doctor.

For people who do not have a high risk of complications, it may not be necessary to see a doctor. However, if symptoms are severe, a doctor may be able to prescribe antiviral medications.

Additionally, people should see a doctor if they have the flu and experience any of the following symptoms:

  • breathing difficulties
  • chest or abdominal pain
  • sudden dizziness
  • confusion
  • severe vomiting
  • symptoms that initially improve, then return with a worse cough

Children should visit a doctor if they show the following signs:

  • rapid breathing
  • changes in skin color
  • not drinking enough fluids
  • high irritability
  • fever with a rash

People in at-risk groups of complications should always contact a doctor if they have the flu.

Summary

The flu is a viral infection that spreads easily. It can occur without a high temperature, or fever, but typically does include this symptom.

A fever is the body’s reaction to the infection and helps it fight back and recover.

The best way to treat the flu is to stay home and rest while keeping hydrated with plenty of clear liquids.

People can consult a doctor if symptoms do not improve or if they experience severe symptoms, such as breathing difficulties, vomiting, or confusion.