The flu, or influenza, is a contagious respiratory illness caused by influenza viruses. It affects the nose, throat, and sometimes the lungs. While it often goes away on its own, it can sometimes lead to serious complications, especially for older adults, young children, and people with weakened immune systems.
Every year, millions of people in the United States catch the flu. It spreads quickly, especially in colder months, and is responsible for many doctor visits and hospital stays. Even though most people recover within a week or two, knowing how to recognize it and treat it early can help prevent more serious problems.
In this article, we’ll walk through what the flu is, how it spreads, the different types, symptoms to watch for, how it’s diagnosed, and the treatment options that can help you feel better faster.
What Is the Flu?
The flu is an illness caused by influenza viruses. These viruses infect the respiratory system, which includes your nose, throat, and lungs. The flu comes on suddenly and can make you feel very sick, very fast. It’s more severe than the common cold and often causes fever, body aches, and extreme tiredness.
Most cases of the flu get better on their own, but for some people, especially those with other health problems, it can lead to more serious conditions like pneumonia, bronchitis, or even heart complications. That’s why it’s important to take it seriously, even if you’re normally healthy.
Influenza viruses are different each year. They change often, which is why a new flu vaccine is needed every season to match the most common strains going around.
Causes and Types of Influenza
The flu is caused by influenza viruses that spread from person to person, usually through tiny droplets released into the air when someone who is infected coughs, sneezes, or talks. These droplets can land in the mouths or noses of people nearby, or on surfaces that others touch.
People can also catch the flu by touching their own mouth, nose, or eyes after touching a surface that has the virus on it. Because the virus spreads so easily, it’s common for it to move quickly through households, schools, and workplaces during flu season.
There are three main types of influenza viruses that affect people: Influenza A, Influenza B, and Influenza C.
Influenza A is the most common and tends to cause the most severe outbreaks. It’s also the type most often responsible for large flu epidemics. It can spread between people and animals, such as birds and pigs.
Influenza B is also common and usually only spreads among humans. It’s often milder than type A but can still lead to serious illness, especially in children and older adults.
Influenza C causes milder symptoms and doesn’t spread as widely. It’s not usually part of the yearly flu vaccine.
Each year, different strains of these viruses circulate. That’s why public health experts track flu patterns and develop a new vaccine to protect people based on the most likely strains for the season.
Symptoms to Watch For
Flu symptoms often come on quickly. You might feel fine in the morning and suddenly very sick by the afternoon. Unlike a cold, which develops slowly and mostly affects the nose and throat, the flu tends to hit your whole body.
The most common flu symptoms include:
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Fever or feeling feverish, with chills
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Body aches or muscle pain
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Fatigue or weakness
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Dry cough
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Sore throat
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Headache
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Runny or stuffy nose
Some people also experience nausea, vomiting, or diarrhea, though this is more common in children than in adults.
Not everyone with the flu will have a fever, but feeling very tired and achy is a classic sign. If you or a loved one starts feeling this way during flu season, it’s a good idea to rest, stay home, and consider seeing a doctor if the symptoms get worse.
How Doctors Diagnose the Flu
In many cases, doctors can diagnose the flu based on your symptoms and the time of year. If the flu is going around and you suddenly have a fever, body aches, and a cough, there’s a good chance you have it.
To be sure, a doctor may use a flu test. There are different types of tests available. Some can give results in less than 15 minutes, while others take a bit longer but are more accurate. These tests usually involve a swab from your nose or throat.
Testing is most useful when it helps guide treatment, especially in people at higher risk of complications. The sooner you know for sure, the sooner you can begin treatment if needed.
Treatment Options and Self-Care
Most healthy people recover from the flu with rest, fluids, and time. There’s no cure, but there are ways to ease your symptoms and help your body heal. The most important things you can do are to stay home, get plenty of rest, and drink enough fluids to stay hydrated.
Over-the-counter medications like acetaminophen or ibuprofen can help reduce fever and relieve body aches. Cough drops, throat sprays, and warm tea with honey can soothe a sore throat or dry cough.
For some people—especially those at higher risk for serious flu complications—doctors may prescribe antiviral medications like oseltamivir (Tamiflu) or baloxavir (Xofluza). These medicines work best when taken within the first 48 hours after symptoms begin. They don’t cure the flu but can help shorten how long you’re sick and reduce the severity of symptoms.
It’s also important to know when to seek medical care. If you have trouble breathing, chest pain, severe weakness, or a high fever that won’t go down, you should contact a doctor right away. Young children, pregnant women, older adults, and people with chronic conditions like asthma or diabetes should be especially careful.
