The flu (influenza) is a viral disease of the respiratory tract. Characteristic symptoms are
Other symptoms can occur, like
- nausea and vomiting,
- muscle or body aches,
- tiredness and fatigue,
- appetite loss,
- sore throat, and
- diarrhea.
Symptoms of the flu usually last for one to two weeks. If vomiting or diarrhea is severe, symptoms of dehydration may develop.
Other conditions can sometimes cause similar symptoms, leading people to wonder if they really have the flu or a different condition. Haemophilus influenzae is a bacterium that was incorrectly considered to cause the flu until a virus was demonstrated to be the correct cause in 1933. This bacterium can cause lung infections in infants and children and can sometimes cause sinus or other infections. Other bacterial or viral infections, including the common cold, may cause symptoms similar to the flu. Sometimes with a runny nose, sneezing, head congestion, chest discomfort, stuffy nose, and cough, it is hard to determine whether a cold or the flu is the cause of the symptoms, although the flu tends to produce higher fever than the common cold. Sometimes, allergies produce severe respiratory symptoms as well. Symptoms of certain complications of the flu, such as pneumonia, lead to similar symptoms.
Causes of the flu (influenza)
Influenza viruses cause the flu (influenza). Influenza viruses are divided into three types, designated influenza types A, B, and C. Influenza types A and B are responsible for epidemics of illness that occur almost every winter and are often associated with increased rates of hospitalization and death. Influenza type C usually causes either a very mild respiratory illness or no symptoms at all.
Other flu
- Body Aches
- Cough
- Diarrhea
- Fatigue
- Fever
- Headache
- Malaise
- Muscle Aches
- Nausea
- Sneezing
- Sore Throat
- Tiredness
- Vomiting

QUESTION
Which illness is known as a viral upper respiratory tract infection? See AnswerPictures, Images, Illustrations & Quizzes
-
A Cold or The Flu? How to Tell the Difference
Discover the difference between cold vs. flu symptoms. Learn the difference between cold and flu symptoms. Read about cold and...
-
Cold & Flu Quiz: Influenza vs. Common Cold
Aches? Pain? Fever? This Cold & Flu Quiz tests your knowledge on the difference between coming down with the common cold and...
-
Cold and Flu: Finding Fast Cough Relief
Remedies for coughing to relieve symptoms, thin mucus, and clear phlegm include cough syrup and honey in hot water. Use...
-
Cold and Flu: The Truth About Hand Sanitizer
Hand sanitizers are a convenient way to kill germs. But do they really work? Here's what we found.
-
Cold and Flu: What Doctors Do to Boost Their Immune Systems
How can you make your immune system stronger? Why not try what the pros try?
-
Cold, Fever and Flu Symptoms in Children: Medications and Home Remedies
How long does a cold last? How long is a cold contagious? Colds and fevers are some of the most common ailments in children....
-
Cold, Flu, & Cough: How to Clean After Illness
This slideshow gives you a room-by-room look at how and what to disinfect after someone in your family has been sick.
-
Cold, Flu, & Cough: Symptoms of Immune System Problems
Your immune system is your main line of defense against infection and illness. Learn the warning signs that yours isn’t working...
-
Cold, Flu, and Cough: 13 Foods to Eat When Fighting the Flu
The best foods to eat when you have the flu soothe symptoms and help you feel better faster. Good foods to eat with the flu...
-
Cold, Flu, and Cough: How to Avoid Infectious Diseases
The right habits will lower your chances of catching an infectious disease. Learn what you can do to help yourself stay healthy.
-
Cold, Flu, and Cough: Things That Suppress Your Immune System
A strong immune system is your best protection against infections and illnesses. Find out what can weaken that defense.
-
Flu Shots: 10 Facts About Flu Shots
What are the side effects of a flu shot? Who should get vaccinated? Learn the benefits and risks of vaccination for seasonal...
-
Home Remedies for Sick Children
Home remedies for sick babies, toddlers, and kids can help with things like colds, flu, cough, sore throat, stuffy nose, fever,...
-
How to Get Rid of a Cold: Natural Remedies
What home remedies work to get rid of a cold fast? Many claim cold symptoms and flu symptoms can be relieved with Echinacea,...
-
Picture of Influenza Virus
The flu is caused by viruses that infect the respiratory tract which are divided into three types, designated A, B, and C. See a...
Examples of Medications for Flu
- acetaminophen/chlorpheniramine/phenylephrine
- Afluria Quadrivalent (Influenza Vaccine)
- artesunate
- benzonatate
- dextromethorphan
- FluMist, FluMist Quadrivalent influenza vaccine live intranasal
- Fluzone High-Dose (Influenza Vaccine)
- Mucinex DM (guaifenesin and dextromethorphan hydrobromide)
- oseltamivir (Tamiflu)
- pau d’arco
- quinine
- rimantadine
- Side Effects of Tamiflu (oseltamivir)
- Types of Coronavirus Disease 2019 (COVID-19) Medications
- Xofluza (baloxavir marboxil)
- Xofluza (baloxavir marboxil) Side Effects, Warnings, and Drug Interactions
- zanamivir (Relenza)
From 
Cold and Flu Resources
Featured Centers
Health Solutions From Our Sponsors
Subscribe to MedicineNet's General Health Newsletter
By clicking Submit, I agree to the MedicineNet's Terms & Conditions & Privacy Policy and understand that I may opt out of MedicineNet's subscriptions at any time.