What Is the Difference Between a Cold and the Flu?
Cold and flu symptoms overlap significantly — but they're different illnesses requiring different responses. Here's how to tell them apart.
General information, not medical advice — see terms of use.
Key differences:
Onset:
- Cold: Symptoms develop gradually over 1–3 days
- Flu: Symptoms come on suddenly and severely
Fever:
- Cold: Rare in adults
- Flu: Very common, often 100–104°F, lasting 3–5 days
Muscle aches and fatigue:
- Cold: Mild if present
- Flu: Severe — the hallmark 'hit by a truck' feeling
Headache:
- Cold: Uncommon
- Flu: Common and often severe
Runny/stuffy nose:
- Cold: Very common
- Flu: Less common
When to see a doctor for flu: Seek attention for difficulty breathing, persistent chest pain, confusion, or symptoms that improve then return with worsening cough and fever. Antiviral medications (Tamiflu) are most effective within 48 hours of symptom onset.
Follow-up questions
How long are you contagious with a cold or flu?
Cold: Contagious 1–2 days before symptoms appear until symptoms resolve, typically 7–10 days. Flu: Contagious 1 day before symptoms through 5–7 days after. You're infectious before you know you're sick.
Does the flu shot actually work?
Yes. The flu vaccine is reformulated annually to match predicted strains. In most years it reduces flu illness by 40–60% and significantly reduces the risk of severe illness, hospitalization, and death even when it doesn't prevent infection entirely.
When should I go to the ER for the flu?
Seek emergency care for: difficulty breathing or shortness of breath, persistent chest pain or pressure, confusion or altered mental status, severe or persistent vomiting, symptoms that improve then return with fever and worsening cough. Children under 2 and adults over 65 with flu symptoms should see a doctor promptly.
This page is general information, not medical advice, and it may not reflect the latest rules where you live. For your own situation, talk to a qualified clinician. Spotted an error? Email per@upperia.se and we will fix it.