Key takeaways

  • The period of time between getting a virus and developing symptoms is known as the incubation period. In cases of the flu, the incubation period can range between 1 and 4 days.
  • People with the flu can spread the virus to others 1 day before symptoms start and up to 5 to 7 days after becoming ill.
  • The flu spreads mostly through tiny respiratory droplets in the air. Preventive measures like hygiene practices are important to stop vulnerable groups from getting sick.

Influenza, often referred to simply as the flu, is a respiratory illness caused by the influenza virus. It’s contagious, meaning it spreads from person to person.

While influenza viruses can circulate year-round, they’re more common in the fall and winter months of the year. This period is referred to as the flu season.

Read on to learn more about how the flu develops and when it becomes contagious.

The typical incubation period for the flu is 2 days, but it can range between 1 and 4 days.

This means that, in most cases, people start to develop flu symptoms a few days after the flu virus enters their body.

Once you have the flu virus, you can spread it to other people around 1 day before you first notice symptoms.

Remember, the average incubation period for the flu is about 2 days. So, if you come into contact with the virus on Saturday morning, it can potentially spread to others by Sunday evening.

By Monday afternoon, you’ll likely start feeling the symptoms that come with the flu. These can range from mild to severe. Some people have no symptoms at all. This does not mean the virus can’t spread to others, though.

The flu tends to be most transmissible within the first 3 days of the illness. Once someone has symptoms, the virus may transmit to others for another 5 to 7 days.

The flu may be contagious for a longer period in children, older adults, and individuals with weakened immune systems.

Unlike the symptoms of the common cold, which develop gradually, the symptoms of the flu often come on suddenly.

The symptoms can include:

  • feeling fatigued, tired, or weak
  • headache
  • stuffy nose
  • sore throat
  • dry cough
  • aches and pains
  • fever or chills, though not everyone experiences this
  • vomiting or diarrhea, though this is more common in children

Most people recover within a few days to 2 weeks, but some may need antiviral drugs, especially if they have a higher risk of developing severe symptoms.

The flu mostly spreads through respiratory particles from coughs and sneezes. If you have the flu and visit a crowded area, those around you can inhale the particles from your breath, coughs, or sneezes and get the virus.

The flu can also transmit through contact with objects or surfaces that have virus particles on them, such as door handles or personal items. The virus can survive on surfaces outside the body for up to 1 day.

If you touch an object with respiratory particles on it and then touch your eyes, nose, or mouth, you may get the flu.

If you already have the flu, there are a few things you can do to reduce your risk of passing it to others:

  • Stay home: The flu can spread quickly in crowded settings, such as schools and offices. Try to limit your contact with others until you’ve been fever-free for at least 24 hours, and do not spend time with people who are sick or vulnerable to complications from flu.
  • Wash your hands: Wash your hands with soap and warm water often, especially after coughing, sneezing, or touching your face. If soap and water aren’t available, use an alcohol-based hand sanitizer.
  • Cover your mouth and nose: When you sneeze or cough, try to do so into a tissue or the crook of your elbow to reduce the spread of respiratory particles. Be sure to dispose of any used tissues as soon as possible.
  • Wear a mask: Consider wearing a mask if you need to leave your home, such as when visiting a doctor’s office.

If you want to avoid the flu altogether, the Centers for Disease Control and Prevention (CDC) recommends getting the seasonal flu shot as your best bet. Here’s a look at the pros and cons of the flu shot.

The flu is a respiratory infection that’s more common in the colder months of the year. The incubation period is typically around 2 days, but can last between 1 and 4 days.

Once you have the virus, it can begin spreading around 1 day before you notice symptoms. Even if a person has no symptoms, the virus can still transmit to others.

While many people experience mild or moderate symptoms and recover within 2 weeks or less, the flu can cause severe complications for some individuals, which is why it is important to prevent the spread of flu.

If you have concerns that you have the flu or could be at a higher risk for severe symptoms, contact a doctor.