What is the Flu? Causes, Symptoms, Treatment, Prevention

The flu is a contagious, respiratory illness caused by influenza viruses. Learn more about what its symptoms are and how to prevent it—so you can avoid it altogether.

What is the flu?

Flu season comes around every year, but have you ever wondered what exactly the flu is? The flu—more formally known as influenza—is a contagious, acute respiratory illness caused by influenza viruses. These viruses are one of the most common causes of respiratory infections in people of all ages and often occur as outbreaks during winter months.1

There are two main types of influenza viruses that affect people: Type A and Type B. Both types are behind the influenza epidemic that hits the United States each year. Millions of people in the U.S. are impacted by the flu annually, with the elderly, infants, and those with chronic diseases being the most severely affected.1–3 Though the flu tends to be less serious in healthy school-age children, it is most prevalent amongst this group.1

Regardless of the type of flu virus, the symptoms often include fever, coughing, runny nose, headaches, and body aches.

Read on to learn more important information about the flu.

What causes the flu?

The flu is caused by viruses. Type A and Type B influenza viruses are what cause the main outbreaks of the flu each year. Type A is often hosted in animals such as such as ducks, chickens, pigs and whales, then passed on to humans, and is often more severe.3 Type B is found only in humans.

Both virus types are commonly spread through droplets that enter the air when people who are infected with the flu cough, sneeze, or talk.

A person with the flu can spread it to someone else that is up to about six feet away. You can also get the flu by touching a surface or object that has a flu virus on it and then touching your eyes, mouth or nose. If you become infected with a flu virus, you develop an immunity to that strain of virus. However, flu viruses regularly mutate.

Each year there tends to be a new strain of flu virus that infects people, and even those who have been sick with the flu before are vulnerable to infection with the new strain.4

What are the different types of flu?

Influenza Type A and influenza Type B are the flu viruses that affect humans. Influenza Type A is the virus type that is associated with pandemics such as H1N1 and H3N2. There is a lot of speculation about the differences in these subtypes of flu viruses that can cause pandemics, as well as the symptoms they may cause and the severity of those symptoms. Research has shown that the specific virus subtype that you are infected with is not highly predictive of the symptoms you will experience or how serious those symptoms become.5

Flu Symptoms

People who are infected with the flu may display no symptoms at all. They can also experience mild or moderate symptoms, and in some cases, severe symptoms.3,6

Flus can feel very much like colds, but the symptoms tend to be more severe and to come on faster.

The most common flu symptoms are:4,7,8

  • Fever
  • Dry cough
  • Muscle and joint aches
  • Fatigue
  • Chills or sweats

How long does the flu last?

Flu symptoms in kids and flu symptoms in adults usually last less than a week.8 Acute symptoms like fever do not generally persist beyond 10 days.

What is the difference between a cold and the flu?

Colds and flus are similar in that they are both caused by viruses and they both induce respiratory symptoms. They are caused, however, by different types of viruses, and flu symptoms tend to be more severe and to come on more rapidly than cold symptoms.3,6

Is the flu contagious?

The flu is highly contagious, and it also has a short incubation period, which means that once someone has been exposed to the flu virus, any infection that occurs is likely to cause symptoms rapidly.

If you become infected with a flu virus, you are likely to start feeling symptoms in 1 to 4 days.9

Flu viruses seem to spread most predominantly through aerosol infection where people become infected because of droplets in the air that contain the virus. The droplets enter the air when someone who is infected with the virus talks, coughs, or sneezes.10 Another way these flu viruses spread is through direct contact with surfaces that contain the virus. Shaking hands is heavily implicated in the transmission of flu from person to person.

A person with the flu can spread it to someone else that is up to about six feet away. The flu is contagious up to one day before symptoms even arise.

It is also important to note that young children can pass on the virus earlier on after exposure and for a longer duration than adults, so young children are contagious for a longer period.10 Given that children are contagious longer and also the most likely to be infected, experts urge vaccination in children to help reduce the overall burden of the annual flu.11

If you think you have the flu, be sure to limit contact with others. Once you’re on the mend, keep in mind that the infection can continue to spread for five to seven days after you get sick so it’s important to continue taking cautionary measures.

How can I treat symptoms from the flu?

Most kids and adults with the flu will recover from the flu symptoms on their own. There are several over-the-counter medications, however, that can help to address multiple symptoms of flu while they last. Many over-the-counter cold and flu medicines treat multiple symptoms. Make sure to identify what flu symptoms you are experiencing so you can get the relief you need.

DayQuil and NyQuil

The flu often comes with lots of uncomfortable symptoms. DayQuil Cold & Flu and NyQuil Cold & Flu can help relieve many of those symptoms while your body recovers from the flu virus. DayQuil Cold & Flu contains the active ingredients dextromethorphan for cough relief as well as acetaminophen to relieve muscle aches and pains, and phenylephrine, a nasal decongestant, to temporarily promote freer breathing. NyQuil Cold & Flu provides the same pain relief and cough suppression, combined with the antihistamine doxylamine succinate, to relieve runny nose.

DayQuil and NyQuil Hot Remedy

You may want to curl up with a medicated hot drink when flu symptoms hit. DayQuil or NyQuil Hot Remedy will do the trick. Dissolve the packet into 8 oz. of hot water, stir, and sip while hot, within 10-15 minutes. The soothing Vicks Vapors will comfort you as you sip on the hot drink. NyQuil Hot Remedy relieves nasal congestion, sore throat, body aches, fever, runny nose, and cough from the flu. DayQuil Hot Remedy relieves nasal congestion, sore throat, body aches, fever, and cough from the flu.

How to Prevent the Spread of the Flu

There are several things you can do to decrease chances of becoming infected with the flu and dealing with the associated symptoms. Here are a few:

  • Get a flu shot each year. Annual flu shots are one of the best ways to prevent getting the flu. Each year, scientists develop a vaccine based on what is known about the current strain to help reduce the overall negative impact of the seasonal flu.12 Because the flu virus regularly mutates, getting a flu shot each year is important for decreasing chances of getting the flu.
  • Practice social distancing. The flu virus spreads when an infected person’s respiratory droplets (think coughing and sneezing) make it into the eyes, mouth, or nose of a not yet infected person. With that said, keep your distance from others to avoid giving them the flu.13,14 It is especially important to maintain distance during the winter months when flu outbreaks are common and to stay away from people who are sick.
  • Keep your hands clean. If you become infected with the flu and did not catch the flu via droplets in the air, chances are you contracted the virus by getting the virus on your hands and transferring the virus to your face. Avoid handshakes, especially with people who are sick and during the winter months when the flu is circulating. Regularly washing your hands with soap and water for 15 to 20 seconds can help to remove viruses that have made their way onto your hands.15–17 In the case that you want to wash your hands but do not have access to soap and water, hand sanitizers can also help to kill viruses.18,19
  • Boost your health. Staying otherwise healthy may reduce your chances of getting the flu by helping your immune system to function properly. These practices, like getting enough sleep, can also help minimize the symptoms and duration of your illness if you get infected with the flu.20
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