Flu Versus a Cold
How to tell influenza, a potentially serious viral illness, from a common cold caused by other respiratory viruses.
Last revised
Key takeaways
- Flu onset: sudden: fever, chills, body aches, headache and exhaustion
- Cold onset: gradual: runny or stuffy nose, sneezing and sore throat
- Most useful single change: Get a flu vaccine every fall.
- Commonest mistake: Antibiotics for a cold or flu; they do not treat viruses.
- See a doctor if any of the signs under "When to get help" below apply to you.
Why it matters
Flu can lead to pneumonia and hospitalization, and antiviral medicines for flu work best when started early, so knowing the difference affects when to call a doctor.
The numbers, in one place
| Measure | Figure |
|---|---|
| Flu onset | sudden: fever, chills, body aches, headache and exhaustion |
| Cold onset | gradual: runny or stuffy nose, sneezing and sore throat |
| Flu antiviral medicine | works best started within 48 hours of symptoms |
| Yearly flu vaccine | everyone 6 months and older, ideally by the end of October |
| Back to normal activities | when symptoms are improving and you have had no fever for 24 hours without medicine |
What helps
- Get a flu vaccine every fall
- Call your doctor early in a flu-like illness if you are 65 or older, pregnant, or have asthma, diabetes, heart disease or another chronic condition
- Rest, drink plenty of fluids and use acetaminophen (Tylenol) or ibuprofen as the label directs
- Wash your hands often and cover coughs and sneezes
What to avoid
- Antibiotics for a cold or flu; they do not treat viruses
- Giving aspirin to children or teens with flu-like symptoms, because of the risk of Reye's syndrome
- Cough and cold medicines in children under 4 without a doctor's advice
In depth
Colds are caused by many viruses, most often rhinoviruses, which mainly infect the nose and throat. The immune response is local, so symptoms such as sneezing, a runny nose and sore throat dominate, and most people feel well enough to carry on. Influenza viruses infect the airways more widely and trigger a stronger body-wide immune response, which is why flu brings fever, chills, aches and exhaustion that can put you in bed.
Flu can also damage the airway lining and weaken defenses, which opens the door to bacterial pneumonia. It can worsen chronic conditions such as asthma, heart failure and diabetes, and it is linked to a higher short-term risk of heart attack. These complications explain why flu causes many hospital stays each year, while colds rarely do.
Several other viruses, including COVID-19 and RSV, cause similar symptoms. You cannot tell them apart reliably by symptoms alone, but the overall pattern helps guide decisions. A test is useful when the result would change care, such as starting a flu antiviral for someone at higher risk.
Signs and symptoms
- Flu: sudden fever or feeling feverish, often with chills
- Flu: muscle and body aches, headache and extreme tiredness
- Cold: sneezing, stuffy or runny nose and a scratchy throat
- Both: cough, which may linger for weeks after the illness ends
- Flu in children: vomiting and diarrhea are more common than in adults
- Older adults with flu may have confusion or weakness without a high fever
Causes and risk factors
- Close contact with sick people and touching contaminated surfaces, then the face
- Seasonal timing: flu peaks in fall and winter, colds circulate year-round
- Not having this season's flu vaccine
- Age 65 or older, pregnancy and young children under 5, who face higher flu risks
- Chronic conditions such as asthma, diabetes, heart disease and obesity
- Smoking, which damages airway defenses
How it is checked
Most colds are diagnosed from symptoms, and no test is needed. For flu, a doctor may diagnose it from symptoms during flu season, especially if flu is circulating widely. Rapid tests from a nose swab are available in many clinics and urgent care centers, and molecular tests are more accurate. Some home tests check for both flu and COVID-19.
If you are seriously ill, a doctor may order a chest X-ray, check oxygen levels and look for bacterial infections. Starting antivirals in high-risk or hospitalized people should not wait for test results when flu is likely.
Related topics
- Colds and Flu: What Published Guidance Supports (Immunity)
- The Evidence on Pneumonia, Without the Hype (Respiratory Health)
- The Evidence on Vaccination in Older Adults, Without the Hype (Healthy Aging)
- Common Childhood Infections: What the Evidence Actually Says (Children's Health)
Where to go next
- The First Steps With Flu Versus a Cold
- Answers to the Common Questions on Flu Versus a Cold
- Infectious Diseases: The Complete Guide
- Measles: What the Evidence Actually Says
- Lyme Disease and Ticks: What Published Guidance Supports
When to get help
Call your doctor if symptoms improve then return with fever and a worse cough, or if a cold lasts more than 10 days. Call 911 for difficulty breathing, chest or belly pain or pressure, new confusion, seizures, severe dehydration, or in a child, fast breathing, bluish lips or face, or ribs pulling in with each breath.
Where this comes from
How this page was put together
Every figure, recommendation and warning above is taken from the guidance named in Where this comes from. Nothing on this page is inferred, summarized or generalized beyond what those bodies publish: where they give a number, it is their number, and where they are silent, so are we. Pages are rebuilt whenever the underlying record changes. Sign-off by a named clinician, where it has happened, is shown at the top of the page along with the date.
Medical disclaimer
This article is general information, not medical advice. It cannot account for your own history, medication or circumstances. Always speak to your doctor, pharmacist or another qualified health professional before making changes that affect your treatment, and never delay seeking medical advice because of something you have read here. In an emergency, call 911.