What's the difference between a cold and the flu?

A sore throat, cough and runny nose are symptoms most people recognise as having a cold or the flu. However, telling whether you have one or the other is often more challenging. Both the flu and colds are caused by viruses that infect your upper respiratory system — this includes your nose, mouth and throat. 

The symptoms of a cold and the flu overlap, which is why it is easy to confuse the two conditions. However, there are key differences that can help you determine which you have, which is what we will explore here. 

What is a cold?

A cold is a viral infection of your upper respiratory system, which can be caused by over 200 different viruses that are present throughout the year. However, colds are most often caused by a group of viruses called rhinoviruses.

Cold symptoms

Cold symptoms usually come on gradually and commonly include a mild cough, a runny or stuffy nose, a sore throat, headaches, sneezing, as well as body aches and mild tiredness. Most people recover from a cold within seven to 10 days, although your symptoms may continue for up to two weeks.

What is the flu?

The flu is caused by specific groups of viruses, namely influenza A, B and C. As with colds, the viruses that cause the flu are present throughout the year. However, influenza viruses tend to be more prevalent, spreading from person to person, during the winter months.

Flu symptoms

Symptoms usually come on faster than with a cold and are more severe. As with a cold, flu symptoms include a cough, a runny or stuffy nose, a sore throat, body aches, headaches and sneezing. The cough is usually dry and hacking and the body aches are stronger than with a cold.

Other flu symptoms include a fever, a loss of smell and/or taste, chills, diarrhoea, nausea, vomiting and severe tiredness (fatigue) that can persist for up to two weeks. Most people recover from the flu in around one to two weeks. 

Comparing a cold, the flu and Covid-19

As with the flu and a cold, Covid-19 is caused by a virus that infects your respiratory system. However, Covid-19 is specifically caused by the coronavirus.

Covid-19 often causes a fever, as does the flu. However, unlike the flu, Covid-19 also often causes breathlessness.

A runny or stuffy nose, a sore throat, headaches, sneezing, as well as body aches and tiredness are also common symptoms of Covid-19, and occur with the flu and a cold too. Both the flu and Covid-19 can cause a loss of smell and/or taste and a dry cough. However, with Covid-19, the cough is usually continuous.

How to tell the difference between a cold and the flu

As both a cold and the flu cause a runny or stuffy nose, sneezing, headaches, tiredness and a cough, it can be difficult to distinguish between the two. However, in general, a cold causes milder symptoms and rarely causes a fever, nausea, vomiting or diarrhoea, which can all occur with the flu. If you do develop a fever with a cold, it is usually mild and will not run as high as with the flu.

Treating a cold and the flu

Antibiotics are not effective at treating the flu or a cold as these medicines target bacteria and both the flu and colds are caused by viruses. If you have a cold, it cannot develop into the flu, or vice versa, as these conditions are caused by different viruses. You can, however, catch a cold and the flu at the same time, although this is rare.

Whether you have the flu or a cold, it is important to drink lots of fluids so you can stay hydrated. You can also take over-the-counter decongestants and painkillers (eg ibuprofen and paracetamol) to ease your symptoms.

If you have the flu and belong to a high risk group ie you are pregnant, very young, aged 65 or older, or have a weakened immune system, your doctor can prescribe anti-viral medication to reduce the severity of your symptoms. However, these medications are not usually effective unless they are taken within 48 hours of your symptoms starting.

When to see a doctor

If you have cold or flu-like symptoms and belong to a high risk group ie are pregnant, very young (aged under two years), aged 65 or older, or have a weakened immune system, see your GP. Based on your symptoms, your GP will assess how likely it is that you have the flu and may prescribe anti-viral medication. 

You should also see your GP if your cold or flu-like symptoms don’t improve or get worse after a week eg you are coughing up green mucus, you are breathless, you develop chest pain or a severe sore throat. You may have developed a complication from your respiratory infection that needs further treatment.  

Complications of the flu and colds

Colds usually get better on their own without treatment. However, they can cause complications, especially if you are very young, aged over 65 or have a weakened immune system. Complications include bronchitis, sinusitis and the bacterial infection strep throat. In rare cases, a cold can cause inflammation of the lungs called pneumonia.

The flu is more likely to lead to complications than a cold. Complications include pneumonia, bronchitis, ear infections, sinus infections and inflammation of the brain called encephalitis.