What is Flu vs. Cold — Key Differences & What to Do?

How to tell influenza from a common cold, what symptoms to watch for, when to test, and when to seek care.

Infectious Diseases

Flu vs. Cold — Key Differences & What to Do

2025-08-30

Intro

Colds and flu are both respiratory infections, but influenza tends to start suddenly, hit harder, and cause higher fever and body aches. Knowing the differences helps you decide on testing, antivirals, and when to seek care.

Key Points

Onset: Flu = sudden; Cold = gradual.
Fever & aches: Flu = higher fever & prominent body aches; Cold = milder.
Cough: Both can cough; flu cough often deeper and more exhausting.
Sore throat/runny nose: More prominent with colds.
Antivirals: Flu may benefit from early antivirals (within 48 hours for higher-risk groups).
Testing: Consider if symptoms are severe, you’re high-risk, or during known flu waves.

Symptom Comparison

Feature	Flu (Influenza)	Common Cold
Onset	Abrupt (hours)	Gradual (1–2 days)
Fever	High (≥38°C / 100.4°F) common	Low-grade or none
Aches & chills	Prominent	Mild
Fatigue	Marked, can be prolonged	Mild–moderate
Headache	Common	Less common
Sore throat	Sometimes	Common
Runny/stuffy nose	Sometimes	Common
Cough	Common, can be severe	Common, milder

When to Test

Severe symptoms or high-risk (pregnancy, age ≥65, chronic heart/lung/kidney disease, diabetes, immunocompromise).
Outbreak exposure (household, school, workplace) during flu season.
If results will change management (e.g., antivirals, isolation).

Treatment

Flu: Rest, fluids, fever relief (paracetamol/acetaminophen or ibuprofen if appropriate).
- Antivirals (e.g., oseltamivir) may be recommended for high-risk patients or severe disease, ideally within 48 hours of symptom onset.
Cold: Symptomatic care—fluids, saline nasal rinse, honey for cough (age >1), decongestants/lozenges as appropriate.

Antibiotics do not treat viral infections like flu or colds.

Red Flags — Seek Urgent Care

Difficulty breathing, chest pain, bluish lips/face.
Confusion, severe dehydration, fainting.
Persistent high fever (>3 days) or fever that improves then returns with worse cough.
In children: fast/labored breathing, lethargy, poor intake/urine, or any cyanosis.
In infants <3 months: any fever ≥38.0°C.

Recovery & Prevention

Most colds resolve in 7–10 days; flu may take 1–2 weeks (fatigue can linger).
Vaccination: Annual flu shot reduces risk of severe disease.
Reduce spread: Stay home when unwell, hand hygiene, cover coughs, consider a mask in crowded indoor spaces when symptomatic.

FAQ

How do I know it’s flu without a test?
The combination of sudden onset, high fever, and body aches during flu season strongly suggests flu, but testing is the only way to be sure.

Do I need antivirals?
If you’re at higher risk or have severe disease, speak to a clinician as soon as symptoms start—treatment works best early.

Can you have flu without a fever?
Yes, especially in older adults or those on certain medications—but it’s less common.