Cold or Flu? How to Tell the Difference

Colds and flu are both caused by viruses and share several symptoms, which is why people mix them up. The clearest difference is not the symptom list but how the illness starts and how bad you feel all over.

How can you tell a cold from the flu?

CDC's comparison is straightforward. A cold comes on gradually, while flu comes on abruptly. With a cold, fever is rare and body aches are slight. With flu, fever is common and usually lasts three to four days, body aches are often severe, and tiredness is the norm rather than the exception.

The NHS puts it another way: flu appears quickly, within a few hours, and makes your whole body feel bad, while a cold develops gradually and mainly affects your nose and throat.

What are the symptoms of each?

CDC lists cold symptoms as a runny nose, a blocked nose, cough, sneezing, sore throat, headache, mild body aches and sometimes fever. They usually peak within two to three days, and the whole cold normally lasts less than a week. More than 200 different respiratory viruses can cause a cold.

Flu symptoms, according to CDC and WHO, include a sudden fever or chills, a cough that is usually dry, sore throat, a runny or blocked nose, muscle and joint aches, headache and severe tiredness. Children may also vomit or have diarrhoea, and the NHS notes that children can get ear pain and swollen glands. WHO says flu symptoms usually appear about two days after exposure, with a range of one to four days, and that most people recover within a week, although the cough can last two weeks or more.

How do you care for a cold or flu at home?

• Rest. Do not try to push through flu
• Drink plenty of fluids
• Stay home while you are unwell so you do not pass it on
• Cover your mouth and nose when you cough or sneeze, and wash your hands often
• Avoid touching your face, and keep away from people who are ill

Antibiotics do not work on colds or flu. The NHS says plainly that antibiotics do not work for viral infections such as flu, so taking them will not shorten the illness. If a fever or aches need easing, ask a pharmacist or doctor which medicine is suitable for your age, and never give aspirin to a child under 16.

Who needs to be more careful with flu?

CDC and WHO list the groups at higher risk of serious illness: adults aged 65 and over, children under 5, pregnant women, people with long-term conditions such as asthma, diabetes or heart disease, and people with weakened immune systems. WHO says annual vaccination is the most effective way to prevent flu, and it matters most for these groups and the people who care for them.

When to get emergency help

CDC lists these emergency warning signs in adults:

• Difficulty breathing or shortness of breath
• Ongoing pain or pressure in the chest or abdomen
• Ongoing confusion or dizziness
• Severe muscle pain or weakness
• Symptoms that improve and then come back worse

In children, get emergency help for fast or laboured breathing, bluish lips or face, muscle pain so severe the child refuses to walk, signs of dehydration, a fever above 40°C (104°F) that does not come down with medicine, or any fever in a baby under 12 weeks old. The NHS also treats chest pain, severe difficulty breathing and coughing up blood as emergencies.

For any of these, call Rescue 1122 where available, or go to the nearest hospital emergency department. For milder illness, see a doctor if symptoms have not improved after seven days, or sooner if you are over 65, pregnant, or have a long-term condition or a weakened immune system.