The symptoms of flu are fever or feeling feverish and chills, cough, sore throat, runny or stuffy nose, muscle or body aches, headaches and fatigue, according to the Centers for Disease Control and Prevention. The agency says the symptoms usually come on suddenly, and that a person may have some or all of them. This page reports what the CDC states and is not personal medical advice.
The symptoms the CDC lists
The CDC's page on the signs and symptoms of flu gives this list:
- Fever or feeling feverish and chills
- Cough
- Sore throat
- Runny or stuffy nose
- Muscle or body aches
- Headaches
- Fatigue (tiredness)
- Vomiting and diarrhea in some people, which the agency says is more common in children than adults
The same page says not everyone with flu will have a fever. The CDC's About Influenza page says some people infected with an influenza virus do not develop any symptoms at all.
When symptoms start and how long they last
| Question | What the CDC says |
|---|---|
| When symptoms start | About two days after exposure, with a range of about one to four days |
| How long illness lasts | Most people recover in a few days to less than two weeks |
| When a person is most contagious | During the first three days of illness |
The first and third rows come from the CDC's About Influenza page, and the second comes from its page on signs and symptoms. The About Influenza page also says some otherwise healthy adults may be able to infect others beginning one day before symptoms develop and five to seven days after becoming sick.
For how much flu is circulating now, see Is flu and respiratory illness high in my state?
Flu, a cold or something else
The CDC says flu and the common cold are both respiratory illnesses but are caused by different viruses. Its comparison of the two describes the onset of a cold as gradual and the onset of flu as abrupt.
The agency's About Influenza page says it can be very difficult to tell flu apart from other viral or bacterial respiratory illnesses based on symptoms alone, and that tests are available to diagnose flu. For the symptoms of norovirus, see What are the symptoms of norovirus?
Emergency warning signs
The CDC says people who have these warning signs should get medical care right away. It lists these signs 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 8 hours, dry mouth, no tears when crying)
- Not alert or interacting when awake
- Seizures
- Fever above 104 degrees Fahrenheit that is not controlled by fever-reducing medicine
- In children younger than 12 weeks, any fever
- Fever or cough that improve but then return or worsen
- Worsening of chronic medical conditions
It lists these signs 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
The CDC says these lists are not all inclusive and that a person should consult a medical provider for any other symptom that is severe or concerning.
What the CDC says about treatment
The CDC's page on flu treatment says antiviral drugs for flu are prescription medicines, and that they work best when started within two days of symptoms beginning. The page says antibiotics do not work against viruses such as influenza.
The same page says people with flu symptoms who are at higher risk of complications, who are very sick or who are worried about their illness should contact a health care provider. The CDC's signs and symptoms page names people 65 and older, people with certain chronic conditions such as asthma, diabetes or heart disease, pregnant women and children younger than 5 among those at higher risk.