Flu symptoms
Influenza (flu) can cause mild to severe illness, and at times can lead to death. Flu is different from a cold. Flu usually comes on suddenly. People who have flu often feel some or all of these symptoms:
- Fever* or feeling feverish/chills
- Cough
- Sore throat
- Runny or stuffy nose
- Muscle or body aches
- Headaches
- Fatigue (tiredness)
- Some people may have vomiting and diarrhea, though this is more common in children than adults
*It's important to note that not everyone with flu will have a fever.
Flu complications
Most people who get flu will recover in a few days to less than two weeks, but some people will develop complications (such as pneumonia) as a result of flu, some of which can be life-threatening and result in death.
Sinus and ear infections are examples of moderate complications from flu, while pneumonia is a serious flu complication that can result from either influenza virus infection alone or from co-infection of flu virus and bacteria. Other possible serious complications triggered by flu can include inflammation of the heart (myocarditis), brain (encephalitis) or muscle (myositis, rhabdomyolysis) tissues, and multi-organ failure (for example, respiratory and kidney failure). Flu virus infection of the respiratory tract can trigger an extreme inflammatory response in the body and can lead to sepsis, the body's life-threatening response to infection. Flu also can make chronic medical problems worse. For example, people with asthma may experience asthma attacks while they have flu, and people with chronic heart disease may experience a worsening of this condition triggered by flu.
People at high risk from flu
Anyone can get sick with flu (even healthy people), and serious problems related to flu can happen at any age, but some people are at high risk of developing serious flu-related complications if they get sick. This includes people 65 years and older, people of any age with certain chronic medical conditions (such as asthma, diabetes, or heart disease), pregnant women, and children younger than five years, but especially those younger than two years old.
What are the emergency warning signs of flu?
People experiencing these warning signs should obtain medical care right away.
In children
- Fast breathing or trouble breathing
- Bluish lips or face
- Ribs pulling in with each breath
- Chest pain
- Severe muscle pain (child refuses to walk)
- Dehydration (no urine for eight hours, dry mouth, no tears when crying)
- Not alert or interacting when awake
- Seizures
- Fever about 104°F
- In children less than 12 weeks, any fever
- Fever or cough that improves but then returns or worsen
- Worsening of chronic medical conditions
In adults
- Difficulty breathing or shortness of breath
- Persistent pain or pressure in the chest or abdomen
- Persistent dizziness, confusion, inability to arouse
- Seizures
- Not urinating
- Severe muscle pain
- Severe weakness or unsteadiness
- Fever or cough that improve but then return or worsen
- Worsening of chronic medical conditions
These lists are not all inclusive. Please consult your medical provider for any other symptom that is severe or concerning.
Cold vs flu
| Signs and Symptoms | Cold | Influenza (Flu) |
| Symptom onset | Gradual | Abrupt |
| Fever | Rare | Usual; lasts 3-4 days |
| Aches | Slight | Usual; often severe |
| Chills | Uncommon | Fairly common |
| Fatigue, weakness | Sometimes | Usual |
| Sneezing | Common | Sometimes |
| Chest discomfort, cough | Mild to moderate; hacking cough | Common; can be severe |
| Stuffy nose | Common | Sometimes |
| Sore throat | Common | Sometimes |
| Headache | Rare | Common |