How Does the Flu Spread? All About Flu Transmission, Contagious Period, and More

To avoid getting the flu (influenza), it helps to understand how it spreads. The flu virus most commonly spreads from person to person through the air. But it also spreads through the surfaces people touch. 

Here’s the good news: There are simple steps you can take to help protect yourself and loved ones from the flu this season.

Is the flu airborne?

Yes, the flu can spread through the air. The flu virus enters the body when you breathe in viral particles through your nose and mouth, or when these particles land on the surface of your eye. Then the virus infects the lining of your respiratory tract (your nose, throat, and lungs). When someone gets infected, they can transmit the virus to the next person when they cough, sneeze, or breathe. 

Droplets vs. aerosols

Respiratory viruses like the flu can actually spread through the air in two ways:

• Droplets are small beads of saliva or mucus that contain the virus. Because they’re bigger and heavier than other small particles, they don’t float in the air for too long. This means they have less time to enter the nose or mouth of someone nearby.

• Aerosols are much smaller than droplets, so they can stay in the air for minutes to hours. An “airborne” virus means it spreads through aerosols.

Both droplets and aerosols are created when you cough, sneeze, or talk. And both can infect nearby people when the particles enter their noses, mouths, or eyes. 

Most experts agree that the flu spreads by droplets. But some studies suggest that the flu virus may be spread by both droplets and aerosols, which would technically make the virus airborne. 

Environmental factors like humidity, temperature, and how crowded a space is impact how quickly flu will spread. It’s difficult, though, to study flu transmission by aerosols and droplets in the real world. So it’s unclear how much each one contributes to the spread of the flu.

How does the flu spread through contact?

The flu can also spread by contact (or touch) with surfaces containing viral particles. Viral droplets are often on the skin or nearby surfaces of people who are sick. The virus can enter your body if you touch one of these surfaces and then touch your eyes, nose, or mouth. 

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How long can the flu virus live on surfaces?

The flu virus can survive on surfaces for hours to days, depending on the type of surface. One study found that the flu survived for up to 2 days on hard surfaces, such as plastic or stainless steel. But it didn’t survive over 12 hours on tissues or cloth. 

The flu probably spreads more often through the air than through contact with surfaces. But it’s still important to take steps to prevent both ways of spreading the flu. 

When is someone with the flu most contagious?

Once you’re exposed to the flu, it may take several days until you develop symptoms. And people can spread the flu before they even know they’re sick — usually starting 1 day before they notice symptoms. But people are most contagious 3 to 4 days after their symptoms start. 

The contagious period typically lasts for a week or longer after symptoms start. If you have a fever, it’s safe to assume that you’re contagious. But keep in mind that you can be contagious without a fever.

Experts recommend that you stay away from others until the fever has been gone for over 24 hours without the help of fever-reducing medications.

How to prevent the flu

Getting your yearly flu shot is one of the best ways to protect yourself from getting the flu. Beyond vaccination, here are other steps you can take to help prevent the flu:

• Keep your distance from people who are sick, and avoid direct contact with them.

• Wash your hands with soap and water frequently. Or use hand sanitizer if soap and water are unavailable.

• Avoid touching your eyes, nose, and mouth.

• Disinfect high-touch surfaces often.

If you have the flu, you can help prevent spreading it by taking these additional precautions:

• Avoid contact with others and stay home until you’re feeling better and you haven’t had a fever for 24 hours without using a fever reducer.

• Wear a mask if you must be around others.

• Cover your mouth with a tissue or your elbow when you cough or sneeze.

How is the flu treated?

Even with the best prevention, you may still get the flu. There’s no cure for the flu. But many people can manage symptoms at home with natural flu remedies, like:

• Getting plenty of rest

• Drinking lots of fluids

• Using a nasal irrigator

• Trying a saltwater gargle to relieve a sore throat

Prescription flu medication is also available. But you’ll need to act quickly, since this works best if you take it within 48 hours of when your symptoms start. 

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Written by:

Joanna Jan, MD

Joanna Jan, MD, is board-certified in internal medicine and licensed to practice medicine in the state of Pennsylvania. In 2017, she received her board certification from the American Board of Internal Medicine.

Edited by:

Alex Eastman, PhD, RN

Alex Eastman, PhD, RN, is a California-based registered nurse and staff medical editor at GoodRx, where he focuses on clinical updates and Latino health.

Reviewed by:

Kerry R. McGee, MD, FAAP

Kerry McGee, MD, FAAP, has over a decade of experience caring for babies, children, and teenagers as a primary care pediatrician. She has a special interest in adolescent health, particularly in adolescent mental health.

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