GoodRx Guide
Flu (Influenza): Symptoms, Causes, and Treatments
Comprehensive information for you or a loved one — including treatment options and discounts on popular medications.
Definition
The flu is a respiratory infection caused by influenza viruses. It’s different from the common cold or COVID-19.
Influenza viruses spread from person to person, either in the air or on surfaces. Flu symptoms are similar to a cold. But they can last longer and be more severe.
Flu season
You can get sick with the flu at any time of the year. But the flu is most common in the fall and winter months. Flu cases tend to start ramping up in October and then peak between December and February.
Sometimes, the flu season peaks a second time later in the year. And, sometimes, the season can extend well into March and April. The exact timing of the flu season varies year by year, depending on which strains of the virus are circulating and how strong the vaccine is.
Types
There are four different types of influenza viruses: A, B, C, and D.
Influenza A and B are responsible for seasonal flu and flu epidemics in humans. Influenza A is most likely to cause pandemics. Both influenza A and B are included in the annual flu vaccine.
Influenza C causes a very mild illness in humans. It doesn’t cause pandemics.
Influenza D is a virus that mostly infects cattle. It doesn’t cause disease in humans.
Millions of people get the flu every year in the U.S. Most people have a mild illness and are fine. But hundreds of thousands of people end up hospitalized with the flu. Of those, many thousands of people — including children — will die from flu-related illnesses every year.
Symptoms
Flu symptoms usually come on more suddenly than the common cold. And they tend to be more severe.
People with the flu will have some (or all) of the following symptoms:
Some people with the flu also have nausea, vomiting, or diarrhea. These symptoms are more common in children.
The flu can also cause sneezing, sore throat, and a runny nose. However, these symptoms are more likely in people who have a common cold.
Severe flu symptoms
Most of the time, you can safely take care of yourself at home. But in some people, flu can turn serious.
Flu can lead to complications like pneumonia (a severe type of chest infection), sinus infections, and ear infections. In some rare but life-threatening cases, flu can cause inflammation of the heart, the brain, and organ failure. It can also cause a bodywide inflammatory response to infection called sepsis.
You should go to the emergency room (ER) if you have any of these symptoms:
Difficulty catching your breath
Fever or cough that gets better, but then returns or worsens
Chest or abdominal pain that doesn’t settle
Headaches, dizziness, or drowsiness
Not urinating, or passing small amounts of dark urine
Difficulty getting out of bed, severe muscle pains, or extreme weakness
Worsening symptoms of an underlying medical condition like asthma, heart failure, or diabetes
In children, the signs might be a little different and harder to spot. You should take your child to the ER if they have:
Difficulty breathing
Bluish lips or face
Ribs pulling in with each breath
Chest or muscle pain
Signs of dehydration, such as not urinating for 8 hours, a dry mouth, or no tears when crying
A change in their level of alertness
A lack of desire to walk
Seizures
Fever above 104°F, or any fever in a child less than 12 weeks old
Fever or cough that gets better, but then returns or worsens
How long does the flu last?
You’ll feel your worst anywhere between 2 and 7 days. But symptoms like fatigue and weakness can linger, and it can take up to a week or two to feel completely better.
Are flu symptoms and COVID symptoms the same?
Pretty much. This wasn’t the case in the first few years of the pandemic, but it is now.
Both the flu and COVID can have all the symptoms listed above. And both COVID and flu symptoms can start within a few days of exposure.
COVID symptoms still tend to last a little longer than the flu. But this can vary from person to person. The best way to tell if you have COVID or the flu is to get tested.
Causes
The flu is caused by influenza viruses. Influenza viruses usually spread through the air. They can also spread by touching contaminated surfaces. If the influenza virus enters your body, it can make you sick.
Anyone can get the flu, even young, healthy people. Some groups of people are more likely to get very sick (or even die) from the flu:
Pregnant women
Children under 5 years old
Adults over 65 years old
People with extreme obesity, such as a body mass index (BMI) of 40 or more
People with chronic illnesses
People experiencing homelessness
Children and teens on certain long-term medications
People who are immunocompromised
People who have had a stroke
Residents of nursing homes or long-term care facilities
Some racial and ethnic groups are also more likely to be hospitalized with the flu, including people who are:
Non-Hispanic Black
Hispanic
Latino
American Indian
Alaska Native
Diagnosis
Most of the time, a healthcare professional can diagnose the flu based on your symptoms. But in some situations, a flu test can be helpful.
There are several tests that can diagnose the flu. Here’s what to know:
A “positive” flu test means you have the influenza virus.
You can be tested for the flu from a nose or throat swab. A healthcare professional might also take a sample of phlegm from your respiratory (breathing) tract.
Many health clinics use a quick 15-minute test, called a rapid influenza diagnostic test (RIDT). Unfortunately, RIDTs only pick up influenza A. They can also be falsely reassuring (false negatives).
Other flu tests are more accurate, but they take longer. These range from 30 minutes for some tests (called “rapid molecular assays”) to a few days for viral cultures.
But keep in mind: You don’t need a flu test to be treated for the flu. If your primary care provider suspects you have the flu, they can still recommend flu medications and home care — even without a positive test result.
Medications
If you’re managing your flu symptoms at home, both over-the-counter (OTC), meaning non-prescription, and prescription medications can help.
OTC flu treatments
OTC options to treat flu symptoms include:
Pain relievers like acetaminophen and ibuprofen
Throat sprays or drops to ease a sore throat
Expectorant cough medicine containing guaifenesin to help you clear congestion from your lungs
Cough suppressants containing dextromethorphan to help keep you from coughing
Decongestants with pseudoephedrine to relieve a runny nose
Saline (saltwater) sprays to clear nasal congestion
Prescription antivirals
Prescription medications called antivirals can also shorten flu illness by 1 or 2 days. They work best if given within 48 hours of the start of symptoms.
Common prescription flu medications include:
Oseltamivir (Tamiflu)
Keep in mind that pharmacies may not always have flu medications in stock, especially during peak flu season.
And lastly, antibiotics only treat bacterial infections. They don’t work on viral infections like the flu.
Home remedies
If you have the flu, the best thing you can do is to stay home, rest, and drink plenty of fluids. If possible, keep your distance from those you live with and wash your hands frequently with soap and water.
Congested noses and coughs can also be managed with home remedies like a humidifier, a hot shower, or steam inhalation. And don’t forget that drinking plenty of water helps to loosen mucus in the nose and chest, and it can soothe sore throats.
If you have a fever, the CDC also recommends you stay home from work, school, and other public places until you’ve been fever-free for at least 24 hours.
Prevention
The best way of treating the flu is to prevent it. That means all adults and children over 6 months should get a flu shot every year (except in very rare cases).
Ideally, you should get a flu shot right at the start of the flu season, before flu viruses start circulating in your community. But you can still get the flu shot later in the year.
There are many ways to get the flu vaccine for little to no cost at:
Health clinics
Pharmacies
Public health departments
Workplaces and schools
Protecting yourself also means taking preventive steps in your everyday life to avoid getting or spreading the flu:
Avoid contact with people who are sick.
Stay away from people if you’re sick.
Cover your coughs and sneezes in your elbow. Or, better yet, in a tissue that you throw away right after. Kids can be taught to cough or sneeze into their shirts.
Wash your hands often with soap and water. If that’s not possible, use an alcohol-based hand rub.
Keep your hands away from your face to avoid spreading germs.
Wear a mask if appropriate.
Frequently asked questions
The flu season is different every year because the viruses that cause it are different every year. Flu viruses have a protein coat around them. The influenza A virus — and, to a lesser extent, the influenza B virus — regularly updates its protein coat. This means that every year, flu viruses behave a little differently. The changes in the protein coat affect how contagious the flu viruses are and how severe the flu illness is.
Every year at the end of the flu season, experts worldwide try to predict what the following year’s flu virus strains will be. The next season’s flu vaccine is made based on these predictions. Some years, the match between what’s predicted and what actually happens is more or less better than others.
Colds and the flu can be difficult to tell apart. Both are respiratory illnesses caused by a virus. However, the viruses involved are different.
Usually, the symptoms of a cold are milder than the flu. The flu tends to come on more suddenly and to be more severe. Fever, chills, and body aches are more likely with the flu than with a cold. Sneezing and a runny or congested nose is more likely to be a sign of a cold than the flu.
Importantly, colds don’t typically lead to complications such as pneumonia, whereas the flu can.
The CDC recommends that all people with suspected flu who have a higher risk of complications receive antiviral medications as soon as possible — without needing to have a positive flu test. For these people, antiviral medications can prevent serious flu complications. This may shorten or even prevent hospitalization, and it could mean the difference between life and death.
In addition, anyone with a flu-like illness who’s sick enough to need hospitalization should get antivirals for treatment.
Finally, the CDC also says that healthcare professionals can decide to give early treatment with antivirals to any non-high-risk people with possible flu. The treatment should be given within 48 hours of the start of symptoms.
References
Centers for Disease Control and Prevention. (n.d.). Pandemic flu.
Centers for Disease Control and Prevention. (2022). Diagnosis for flu.
Centers for Disease Control and Prevention. (2024). Cold versus flu.
Centers for Disease Control and Prevention. (2024). Flu season.
Centers for Disease Control and Prevention. (2024). Flu: What to do if you get sick.
Centers for Disease Control and Prevention. (2024). Key facts about seasonal flu vaccine.
Centers for Disease Control and Prevention. (2024). People at increased risk for flu complications.
Centers for Disease Control and Prevention. (2024). Preventing seasonal flu.
Centers for Disease Control and Prevention. (2024). Selecting viruses for the seasonal influenza vaccine.
Centers for Disease Control and Prevention. (2024). Types of influenza viruses.
Morbidity and Mortality Weekly Report (MMWR). (2024). Prevention and control of seasonal influenza with vaccines: Recommendations of the Advisory Committee on Immunization Practices (ACIP)—United States, 2024-25 Summary of recommendations. Centers for Disease Control and Prevention.
National Heart, Lung, and Blood Institute. (n.d.). Calculate your body mass index. National Institutes of Health.
Tokars, J. I., et al. (2018). Seasonal incidence of symptomatic influenza in the United States. Clinical Infectious Diseases.
