Influenza, commonly called the flu, is a contagious respiratory illness caused by influenza viruses. It can range from a mild infection to a serious illness, especially for older adults, very young children, pregnant people, and those with certain medical conditions.
What Is the Flu?
The flu is a viral respiratory infection that affects the nose, throat, and lungs. It often begins suddenly, unlike a common cold, which may develop more gradually. Influenza can spread when an infected person coughs, sneezes, talks, or releases virus-containing particles into the air.
Several influenza viruses circulate over time, and the strains that spread can change. This is one reason seasonal vaccination is recommended and why having the flu once does not provide lifelong protection against every future strain.
Common Flu Symptoms
Flu symptoms often appear one to four days after exposure. Common signs include fever or chills, muscle aches, and marked tiredness. Not everyone with influenza develops a fever.
- Fever, chills, or feeling feverish
- Cough, often dry or persistent
- Sore throat
- Runny or stuffy nose
- Headache
- Body or muscle aches
- Fatigue and weakness
- Occasionally, nausea, vomiting, or diarrhea, particularly in children
Symptoms can overlap with COVID-19, a cold, and other respiratory infections. Symptoms alone cannot always identify the cause, so testing or medical advice may be useful when the diagnosis affects treatment or precautions.
Flu Symptoms in Children
Children may have the usual respiratory symptoms along with poor appetite, irritability, or stomach symptoms such as vomiting and diarrhea. Infants and young children may not be able to describe how they feel, so changes in feeding, behavior, sleep, or breathing are important to notice.
Contact a healthcare professional promptly if a child has trouble breathing, signs of dehydration, unusual sleepiness, a seizure, worsening symptoms, or a fever in an infant. Follow age-specific medical guidance rather than giving medicines intended for adults.
What Causes the Flu?
Influenza viruses cause the flu and spread mainly through respiratory particles and close contact. Infection may also occur after touching a contaminated surface and then touching the mouth, nose, or eyes, although direct respiratory spread is an important route.
A person can spread influenza before symptoms begin and while ill. Crowded indoor spaces, close household contact, and poor ventilation can make transmission more likely. People are generally most contagious during the first few days of illness, but the infectious period varies.
How Long Does the Flu Last?
For many otherwise healthy people, the most intense flu symptoms improve within three to seven days. However, cough and low energy may continue for several days or even a few weeks after the fever and aches have eased.
Recovery may take longer in young children, older adults, pregnant people, and those with chronic health conditions. Seek medical advice if symptoms are not improving, improve and then become worse, or interfere significantly with drinking, breathing, or normal activity.
How the Flu Is Treated
Treatment usually focuses on rest, fluids, and relief of uncomfortable symptoms. Rest and hydration support recovery, while fever relief may make it easier to sleep and drink enough.
- Rest and avoid strenuous activity while feeling unwell.
- Drink water, broth, or other suitable fluids to help prevent dehydration.
- Use over-the-counter fever or pain medicine only as directed on the label or by a healthcare professional.
- Consider warm liquids, throat soothing measures, or a humidified environment for comfort.
- Stay home and limit close contact with others while symptoms are significant.
Antibiotics do not treat influenza because it is caused by a virus. They may be prescribed only when a healthcare professional identifies a separate bacterial infection.
Antiviral Medicines
Prescription antiviral medicines may help some people, especially when started early in illness. They are particularly important to discuss with a clinician if you are pregnant, have a chronic condition, are very young or older, or have severe or worsening symptoms.
Antivirals are not appropriate for everyone, and the choice depends on factors such as symptoms, health history, possible exposure, and local medical guidance. Contact a healthcare professional as soon as possible if you may be at higher risk of complications.
When to Seek Urgent Medical Care
Get urgent medical help for difficulty breathing, chest pain, or sudden confusion. Emergency warning signs can also include bluish or gray lips or face, severe weakness, inability to stay awake, or signs of serious dehydration.
In children, urgent symptoms may include fast or labored breathing, ribs pulling in with each breath, no tears or very little urination, a seizure, or a child who is difficult to wake. If you are unsure how serious the symptoms are, contact a medical professional or local emergency service.
How to Prevent the Flu
Annual flu vaccination is a key prevention measure and can reduce the risk of influenza and its complications. Additional protection includes handwashing, better ventilation, and staying home when sick.
- Wash your hands regularly with soap and water or use hand sanitizer when appropriate.
- Cover coughs and sneezes with a tissue or your elbow.
- Avoid sharing cups, utensils, and personal items during illness.
- Improve indoor airflow when possible.
- Follow current guidance from trusted public health or medical authorities.
Vaccination, hygiene, and staying away from others while contagious work together to reduce spread. If you have a weakened immune system or another condition that raises your risk, ask a healthcare professional about personalized prevention advice.
Flu or a Cold?
The flu commonly causes rapid onset, stronger body aches, and more pronounced fatigue than a typical cold. Colds more often produce a runny or stuffy nose and milder symptoms. Still, there is considerable overlap, and testing may be needed to tell influenza from other infections.
Regardless of the cause, rest, fluids, monitoring symptoms, and avoiding close contact while sick are sensible steps. Seek medical advice when symptoms are severe, persistent, or occurring in someone at higher risk.
Key Takeaways
The flu is a contagious viral illness that often begins suddenly with fever or chills, cough, aches, headache, and fatigue. Most people improve within a week, although cough and tiredness can last longer. Early medical advice, especially for high-risk people, can help determine whether antiviral treatment is appropriate.
Remember the essentials: rest and hydrate, monitor for warning signs requiring urgent care, avoid spreading the infection, and seek urgent care for breathing problems, chest pain, confusion, severe dehydration, or rapidly worsening symptoms.
