They share many symptoms, but fever, body aches, itchy eyes and how fast it starts give clues. A side-by-side table, what helps each one and the warning signs to act on.
Why they're easy to mix up
Colds, flu and COVID-19 are infections caused by viruses. Seasonal allergies are not an infection at all: they happen when your immune system overreacts to something harmless, such as pollen, dust mites, mold or pet dander. All four can give you a runny or stuffy nose, sneezing and a cough – but a few symptoms point more strongly to one than the others.
Symptoms side by side
| Symptom | Cold | Flu | COVID-19 | Allergies |
|---|---|---|---|---|
| How it starts | Gradually | Suddenly | Gradually or suddenly | When you meet the trigger |
| Fever | Rare in adults | Common, often high | Common | Never |
| Body aches and chills | Mild | Common, often severe | Common | No |
| Tiredness | Mild | Common, can last weeks | Common | Sometimes |
| Sneezing | Common | Sometimes | Sometimes | Very common |
| Stuffy or runny nose | Common | Sometimes | Common | Very common |
| Sore throat | Common | Sometimes | Common | Sometimes, from postnasal drip |
| Cough | Mild to moderate | Common, can be severe | Common | Sometimes |
| Itchy, watery eyes | Rare | Rare | Rare | Very common |
| New loss of taste or smell | Rare | Rare | Possible | Rare |
| How long it lasts | 7–10 days | 1–2 weeks | Varies | As long as you're exposed |
Two quick clues: itchy eyes and no fever point to allergies, and a sudden start with fever and aches points to flu or COVID-19. Children with a cold get a fever more often than adults do.
Flu and COVID-19 can look exactly alike, so a test is the only way to know – a home COVID-19 test, or a test at a clinic. It matters because prescription antiviral medicines work best when they're started early: within about 2 days for flu, and within 5 days for COVID-19. That's especially important if you're 65 or older, pregnant, or have a long-term condition such as asthma, diabetes or heart disease.
What helps
A cold
There's no cure for the common cold, and antibiotics don't work on it. Rest, drink plenty of fluids and treat the symptoms that bother you:
- Aches, sore throat or fever: acetaminophen or ibuprofen
- Chest congestion: guaifenesin thins mucus so coughs bring it up more easily
- Several symptoms at once: a multi-symptom product such as Day & Night Cold and Flu Relief
Many cold and flu products already contain acetaminophen. Check every label and never take more than one product with the same ingredient.
Flu
Treat the symptoms the same way, rest, and stay home until you've been fever-free for 24 hours without a fever reducer and you feel better overall. If you're in a higher-risk group, call your doctor as soon as symptoms start – an antiviral may help. A yearly flu vaccine is the best protection.
COVID-19
Symptom relief is the same as for flu. Test, follow current CDC advice about staying home, and contact your doctor early if you're at higher risk, as antiviral treatment may be an option.
Allergies
Avoid your triggers where you can, and try a non-drowsy antihistamine such as cetirizine or loratadine. A steroid nasal spray such as fluticasone works well for a blocked nose when used every day. Our guide to managing seasonal allergies has more tips.
When to see a doctor
Contact a doctor if:
- Symptoms last more than 10 days, or get better and then worse again
- You have a high fever, or a fever that lasts more than 3 days
- You have pain in your face or forehead with thick, discolored mucus, or ear pain
- You're in a higher-risk group and think you have flu or COVID-19
Call 911 for trouble breathing, chest pain or pressure that doesn't go away, new confusion, blue or gray lips or face, a seizure, not urinating, or severe weakness.
Frequently asked questions
Can allergies cause a fever?
No. Seasonal allergies don't cause a fever. If you have a fever, an infection is more likely.
Do I need antibiotics for a cold or the flu?
No. Both are caused by viruses, and antibiotics only work against bacteria. Taking them when they aren't needed can cause side effects and makes antibiotic resistance more likely.