What the Guidance Really Says About Flu Versus a Cold

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 speak to a doctor" below apply to you.

What it is

How to tell influenza, a potentially serious viral illness, from a common cold caused by other respiratory viruses. It sits within Infectious Diseases. The figures come from the bodies named at the foot of this page.

The numbers, in one place

What helps

You do not have to do all of it, and you do not have to start today.

• 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

These come up often, and several of them sound like good ideas.

• 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.

Treatment and support options

Flu antivirals

Prescription antiviral medicines can shorten flu and reduce the risk of complications. They are especially recommended for people at higher risk and anyone hospitalized. They work best when started early, but a doctor may still prescribe them later for people who are very sick or at high risk. Side effects can include nausea.

Symptom relief

Rest and fluids help with both illnesses. Acetaminophen (Tylenol) or ibuprofen can ease fever and aches. Saline sprays and humidified air help a stuffy nose. Honey can ease a cough in adults and children over 1 year. Check that you are not taking acetaminophen in several combination products at once.

Over-the-counter cold medicines

Decongestants and antihistamines may relieve some symptoms in adults but do not shorten a cold. Decongestants can raise blood pressure and heart rate, so check with a pharmacist if you have heart disease or high blood pressure. Read labels carefully, since many multi-symptom products contain the same ingredients.

Knowing when to seek care

Most people with a cold do not need to see a doctor. With flu-like symptoms, contact your doctor early if you are at higher risk. Anyone with warning signs, such as difficulty breathing or symptoms that improve then worsen, needs prompt care.

Prevention

• Get a flu vaccine every year
• Wash your hands with soap and water or use hand sanitizer
• Avoid touching your eyes, nose and mouth
• Stay home when sick to protect others
• Clean frequently touched surfaces during cold and flu season
• Improve indoor ventilation when people are sick at home

Day to day

Recovering from flu often takes a week or more, and tiredness and cough can linger for several weeks. Return to work, school and exercise gradually. If fatigue or breathlessness keeps you from normal activity well after the illness ends, check in with your doctor.

At home, care for sick family members while protecting yourself: wash hands after contact, avoid sharing utensils and towels, and keep high-risk people away from the person who is sick if possible. If you live with someone at high risk, ask your doctor whether they should take an antiviral to prevent flu after exposure.

For specific groups

Young children

Children under 5, especially under 2, are at higher risk of flu complications. Watch for fast breathing, dehydration, high fever or unusual sleepiness. Antivirals are available for children; call their doctor early.

Pregnancy

Flu is more likely to be severe during pregnancy and for two weeks after birth. The flu shot is recommended in any trimester, and antivirals are recommended if you develop flu symptoms.

Older adults

People 65 and older are at the highest risk of hospitalization from flu. Higher-dose or enhanced flu vaccines are preferred for this age group. Early antiviral treatment is important.

Questions to ask your doctor

• Am I in a group at higher risk from flu?
• Which flu vaccine is best for me?
• Should I take an antiviral if I get flu symptoms?
• Are cold medicines safe with my other medicines and conditions?
• When should I be tested for flu or COVID-19?

More questions, answered

Can the flu shot give me the flu?

No. Flu shots contain inactivated virus or a single protein and cannot cause flu. Some people feel achy or have a sore arm for a day or two, which reflects the immune system responding.

Why do I need a flu vaccine every year?

Flu viruses change, and vaccines are updated each season to match. Protection also fades over months. A yearly vaccine gives you the best match and the strongest protection.

Does vitamin C or zinc prevent colds?

Evidence is mixed and generally shows small effects at best. Vitamin C does not prevent colds for most people, and zinc nasal products have caused loss of smell. Talk to your doctor or pharmacist before using supplements.

Is a stomach bug a form of flu?

No. "Stomach flu" usually refers to viral gastroenteritis, often norovirus, which is different from influenza. Flu is a respiratory illness, though some children with flu do vomit.

How long am I contagious with flu?

People with flu are most contagious in the first few days of illness. Some people, especially young children and those with weakened immunity, can spread it for longer. Follow guidance about staying home until fever has been gone for 24 hours without medicine.

Can I get flu even after being vaccinated?

Yes, but vaccination lowers the risk of illness and makes severe illness, hospitalization and death less likely. The vaccine is still worth getting even if it does not prevent every case.

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

• Answers to the Common Questions on Flu Versus a Cold
• Flu Versus a Cold: Just the Figures
• Flu Versus a Cold — the reference entry
• Infectious Diseases: The Complete Guide
• Measles: What the Evidence Actually Says
• Lyme Disease and Ticks: What Published Guidance Supports

When to speak to a doctor

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

• CDC — Cold Versus Flu
• CDC — Treating Flu with Antiviral Drugs

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.