What counts as flu symptoms

TL;DR:

Flu starts fast with fever, cough, aches, and deep fatigue.
Not everyone gets a fever, older adults may not.
Kids can have vomiting or ear pain along with typical signs.
Most recover at home, seek care if breathing, chest pain, or confusion occur.
High risk groups should call a doctor early for antivirals.

Influenza is a respiratory infection that hits hard and fast. The U.S. Centers for Disease Control and Prevention lists common signs as fever or chills, cough, sore throat, runny or stuffy nose, muscle and body aches, headache, and fatigue. Vomiting and diarrhea can occur, more often in children than adults, and some people never run a fever at all. Symptoms usually start suddenly and can range from mild to severe, according to the CDC. The World Health Organization describes a similar pattern, with sudden onset fever, dry cough, headache, muscle and joint pain, sore throat, and severe tiredness. Mayo Clinic notes that people often feel much worse with flu than with a cold, and symptoms commonly include fever, cough, headache, muscle aches, chills, and profound fatigue.

The quick checklist

Use this fast scan to decide if your illness looks like flu.

Sudden start, you felt fine then felt awful within hours
Fever or chills, though fever may be absent in some people
Dry cough and sore throat
Body and muscle aches, often severe
Headache and deep fatigue
Runny or stuffy nose
Children may also vomit or have diarrhea

If most boxes match, flu is likely.

How flu feels over time

Incubation and onset

Flu symptoms usually begin 1 to 4 days after exposure. The start is abrupt. Many people can recall the exact hour they “hit the wall.” Fever, aches, and fatigue peak in the first 2 to 3 days.

Days 3 to 7

Fever often eases by day 3 to 4. A dry cough and fatigue linger. Sore throat and congestion may continue. Appetite is low. Sleep can be poor.

Weeks 1 to 2

Cough and tiredness can last two weeks or more, even as you return to normal tasks. WHO notes cough may persist for two or more weeks.

Flu vs cold vs COVID at a glance

You cannot tell for sure without a test, but patterns help.

Feature	Flu	Common cold	COVID-19
Onset	Sudden, within hours	Gradual	Can be sudden or gradual
Fever	Common, may be high	Rare or low	Common, any level
Aches	Common, can be severe	Mild	Common
Fatigue	Marked	Mild to moderate	Common
Cough	Dry, persistent	Mild to moderate	Common
Sore throat	Common	Very common	Common
Loss of smell	Uncommon	Sometimes	More common than with flu
Stomach upset	Children more than adults	Uncommon	Sometimes

Testing guides care. If you are high risk or very unwell, call a clinician to ask about flu or combined flu and COVID tests. Mayo Clinic notes multiplex tests are available in many settings.

Who is at higher risk from flu

Some people face higher odds of severe illness or complications. If you or a loved one is in one of these groups and flu symptoms start, contact a doctor quickly to discuss antivirals.

Adults 65 and older
Children under 5, especially under 2
Pregnant or up to 2 weeks after delivery
People with long term lung, heart, kidney, liver, or metabolic disease
People with weakened immune systems
People with obesity

This list aligns with public health guidance from CDC and WHO. If unsure, call your clinician.

Red flag symptoms, get urgent care

Most people can manage at home, but some signs need same day care. Mayo Clinic advises seeking care right away for:

Trouble breathing or shortness of breath
Chest pain or pressure
New confusion, fainting, or seizures
Severe weakness or muscle pain
Worsening of long term conditions, like asthma or heart disease
Dehydration signs, such as no urination for 8 hours, very dry mouth, dizziness

Children need urgent care for fast or labored breathing, bluish lips or face, severe dehydration, persistent high fever, or if they are very sleepy, hard to wake, or not interacting.

How long you are contagious

People are most contagious in the first 3 to 4 days after illness starts, but can spread virus from about a day before symptoms until at least 5 to 7 days after. Young children and people with weak immune systems may spread for longer. This pattern comes from CDC summaries of flu transmission.

Home care that actually helps

Simple steps help most people recover.

Rest. Your body needs energy to fight the virus.
Fluids. Aim for pale yellow urine. Use oral rehydration if needed.
Fever and pain relief. Acetaminophen or ibuprofen as labeled, unless a doctor says otherwise.
Avoid aspirin in children and teens.
Honey for cough if over age 1. Avoid in infants.
Saline spray, steam, or a humidifier for congestion.
Light meals, broths, or soups if appetite is low.

Antivirals

If started within 48 hours of symptom start, antivirals can shorten illness and lower the risk of complications, especially in high risk groups. Ask a clinician about options if you qualify. Treatment can still help even after 48 hours for severe or progressive illness. This approach is consistent with CDC and Mayo Clinic guidance.

Common mistakes to avoid

Waiting too long to call if you are high risk. Early treatment matters.
Assuming it is “just a cold” when symptoms start fast and hit hard.
Returning to work or school while feverish. Stay home until fever free for 24 hours without fever reducers.
Using antibiotics for flu. Flu is viral. Antibiotics do not help unless there is a bacterial complication.
Giving aspirin to children or teens. Risk of Reye’s syndrome.
Ignoring dehydration, especially in kids and older adults.

When to test

Testing is most useful if you are high risk, very unwell, in a setting with outbreaks, or if a positive result would change treatment. Combined tests for flu and COVID exist. Clinicians can advise which test makes sense based on your setting and timing. Mayo Clinic and CDC clinical pages explain that rapid antigen tests give quick answers, while PCR tests are more sensitive.

A short symptom checklist to print

Symptoms began suddenly
Fever or chills
Dry cough
Sore throat
Muscle or body aches
Headache
Fatigue
Runny or stuffy nose
For children, vomiting or diarrhea
I am in a high risk group
Red flag symptoms present

If you checked many of the top items and any of the last two, call your doctor today.

Prevention, in one minute

Get a flu shot each season.
Wash hands with soap and water for 20 seconds.
Cover coughs and sneezes.
Improve airflow at home and work.
Stay home when sick.
Consider a well fitting mask in crowded indoor spaces during peak flu weeks.

These steps line up with WHO and CDC prevention advice.

Why it matters

Flu spreads fast, and it can cause serious illness in some people. Knowing the key symptoms helps you act early, protect family members, and reduce spread at school or work. Quick action can also unlock antiviral treatment for those who need it most.