Every fall and winter, millions of Americans wake up with a sore throat and a stuffy nose and wonder whether it is a cold they can sleep off or the flu. The question matters more than it seems. Flu can be serious, especially for older adults, young children and people with chronic conditions, and the medicines that treat it work best when started early.

The quickest clue: how fast it started

A cold usually creeps up over a day or two, starting with a scratchy throat and a runny nose. The flu tends to hit abruptly. People often say they felt fine in the morning and terrible by the afternoon.

Typical flu symptoms, according to the CDC, include fever or chills, cough, sore throat, a runny or stuffy nose, muscle and body aches, headache and exhaustion. Vomiting and diarrhea are more common in children than adults. Not everyone with the flu has a fever.

Colds rarely cause high fever or severe body aches, and people with a cold can usually keep going about their day, if unhappily.

What about COVID-19 and RSV?

COVID-19 and RSV can look a lot like the flu, and symptoms overlap so much that you often can’t tell them apart without a test. Home tests for COVID-19 are widely available, and some pharmacies and clinics offer combined tests for COVID-19 and flu. Testing helps because the treatments are different, and some of them must be started early.

Why the first two days matter

Flu is a virus, so antibiotics won’t help. Prescription antiviral medicines can, and the CDC says they work best when started within two days after symptoms begin. They can shorten the illness and lower the risk of complications such as pneumonia. The CDC recommends treating people with suspected flu as early as possible if they are at higher risk or very sick, and later treatment can still help those groups.

Higher-risk groups include adults 65 and older, young children, pregnant people and anyone with conditions such as asthma, diabetes or heart disease. If you are in one of those groups and think you have the flu, call your doctor or use a telehealth service on the first day rather than waiting to see if it gets better.

Emergency warning signs in adults

Get medical care right away for:

  • Trouble breathing or shortness of breath.
  • Pain or pressure in the chest or belly that doesn’t go away.
  • Ongoing dizziness, confusion, or being hard to wake.
  • Seizures.
  • Not urinating, severe muscle pain, or severe weakness or unsteadiness.
  • A fever or cough that gets better and then returns or gets worse.
  • A chronic condition, such as asthma or heart disease, that is getting worse.

Emergency warning signs in children

In addition to many of the signs above, watch for:

  • Fast or labored breathing, or the ribs pulling in with each breath.
  • Bluish lips or face.
  • Signs of dehydration, such as no urine for eight hours, a dry mouth or no tears when crying.
  • Not being alert or interacting when awake, or severe muscle pain that makes a child refuse to walk.
  • A fever above 104°F that doesn’t come down with fever medicine, or any fever in a baby younger than 12 weeks.

These lists aren’t complete. Trust your instincts: if someone seems seriously ill, get help.

When home care is enough

Most healthy adults and older children with a cold or mild flu recover in about a week without a doctor. Rest, drink plenty of fluids, and use over-the-counter medicines for fever and aches if they are safe for you, following the label. Don’t give aspirin to children or teenagers with flu-like illness. A cough can linger for a couple of weeks after other symptoms fade.

Protecting the people around you

Stay home while you have a fever and for at least a day after it goes away without fever medicine. Cover coughs and sneezes, wash your hands often and keep away from vulnerable relatives while you are sick. Ask your doctor or pharmacist which vaccines are recommended for you this season.

What we think

The most useful habit this winter is simple: if you or a high-risk family member suddenly feels very sick, call a doctor on day one instead of day four. That small change gives antivirals their best chance to work and catches complications before they become emergencies.

This article is general information, not medical advice. If you have symptoms or questions about your own health, talk to a doctor, nurse or pharmacist. In an emergency, call 911.