About flu

Flu (influenza) is a common infectious viral illness spread by coughs and sneezes. It can be very unpleasant, but you'll usually begin to feel better within about a week.

You can catch flu all year round, but it's especially common in winter, which is why it's also known as seasonal flu.

Flu isn't the same as the common cold. Flu is caused by a different group of viruses and the symptoms tend to start more suddenly, be more severe and last longer.

Flu symptoms

Some of the main symptoms of flu include:

  • a high temperature (fever) of 38C (100.4F) or above
  • tiredness and weakness
  • headache
  • general aches and pains
  • a dry, chesty cough

Cold-like symptoms, such as a blocked or runny nose, sneezing, and a sore throat, can also be caused by flu, but they tend to be less severe than the other symptoms you have.

Flu can make you feel so exhausted and unwell that you have to stay in bed and rest until you feel better.

Read more about the symptoms of flu

Flu-like illness self-help guide

If you have a flu-like illness, complete our self-help guide to assess your symptoms and find out what to do next.

Self-help guide: Flu-like illness

What to do

If you're otherwise fit and healthy, there's usually no need to see your GP if you have flu-like symptoms.

The best remedy is to rest at home, keep warm and drink plenty of water to avoid dehydration. You can take paracetamol or ibuprofen to lower a high temperature and relieve aches if necessary.

Stay off work or school until you're feeling better. For most people, this will take about a week.

Read more about treating flu at home

When to see your GP

Consider visiting your GP if:

  • you're 65 years of age or over
  • you're pregnant
  • you have a long-term medical condition – such as diabetes, heart disease, lung disease, kidney disease or a neurological disease
  • you have a weakened immune system – for example because you're having chemotherapy or have HIV
  • you develop chest pain, shortness of breath, difficulty breathing or start coughing up blood
  • your flu symptoms are getting worse over time or haven't improved after a week

In these situations, you may need medication to treat or prevent complications of flu. Your GP may recommend taking antiviral medicine to reduce your symptoms and help you recover more quickly.

Read more about antiviral medication for flu

How long does flu last and is it serious?

If you have flu, you generally start to feel ill within a few days of being infected.

You should begin to feel much better within a week or so, although you may feel tired for much longer.

You'll usually be most infectious from the day your symptoms start and for a further 3 to 7 days. Children and people with weaker immune systems may remain infectious for longer.

Most people will make a full recovery and won't experience any further problems, but elderly people and people with certain long-term medical conditions are more likely to have a bad case of flu or develop a serious complication, such as a chest infection.

Read more about the complications of flu

How you catch flu

The flu virus is contained in the millions of tiny droplets that come out of the nose and mouth when someone who is infected coughs or sneezes.

These droplets typically spread about one metre. They hang suspended in the air for a while before landing on surfaces, where the virus can survive for up to 24 hours.

Anyone who breathes in the droplets can catch flu. You can also catch the virus by touching the surfaces that the droplets have landed on if you pick up the virus on your hands and then touch your nose or mouth.

Everyday items at home and in public places can easily become contaminated with the flu virus, including food, door handles, remote controls, handrails, telephone handsets and computer keyboards. Therefore, it's important to wash your hands frequently.

You can catch flu many times because flu viruses change regularly and your body won't have a natural resistance to the new versions.

Preventing the spread of flu

You can help stop yourself catching flu or spreading it to others with good hygiene measures.

Always wash your hands regularly with soap and warm water, as well as:

  • regularly cleaning surfaces such as your computer keyboard, telephone and door handles to get rid of germs
  • using tissues to cover your mouth and nose when you cough or sneeze
  • putting used tissues in a bin as soon as possible

You can also help stop the spread of flu by avoiding unnecessary contact with other people while you're infectious. You should stay off work or school until you're feeling better.

In some people at risk of more serious flu, an annual flu vaccine or antiviral medication may be recommended to help reduce the risk of becoming infected.

Read more about how to stop the spread of flu

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

Symptoms of flu

The symptoms of flu usually develop within 1 to 3 days of becoming infected. Most people will feel better within a week.

However, you may have a lingering cough and still feel very tired for a further couple of weeks.

Main symptoms

Flu can give you any of the following symptoms:

  • a sudden fever – a temperature of 38C (100.4F) or above
  • a dry, chesty cough
  • a headache
  • tiredness and weakness
  • chills
  • aching muscles
  • limb or joint pain
  • diarrhoea or abdominal (tummy) pain
  • nausea and vomiting
  • a sore throat
  • a runny or blocked nose
  • sneezing
  • loss of appetite
  • difficulty sleeping

Is it flu or a cold?

It can sometimes be difficult to tell if you have flu or just a cold, as the symptoms can be quite similar. The main differences are:

Flu symptoms:

  • come on quickly
  • usually include fever and aching muscles
  • make you feel too unwell to continue your usual activities

Cold symptoms:

  • come on gradually
  • mainly affect your nose and throat
  • are fairly mild, so you can still get around and are usually well enough to go to work

When to visit your GP

If you are otherwise fit and healthy, there's usually no need to visit your GP if you have flu-like symptoms.

You should just rest at home until you feel better, while keeping warm, drinking plenty of water and taking painkillers if necessary.

Read more about how to treat flu

Consider visiting your GP if:

  • you're 65 years of age or over
  • you're pregnant
  • you have a long-term medical condition – such as diabetes, heart disease, lung disease, kidney disease or a neurological disease
  • you have a weakened immune system – for example, because you're having chemotherapy or have HIV
  • you develop chest pain, shortness of breath or difficulty breathing, or start coughing up blood
  • your symptoms are getting worse over time or haven't improved after a week

In these situations, you may need extra treatment to prevent or treat complications of flu.

Treating flu

Usually, you can manage flu symptoms yourself at home and there's no need to see a GP. Most people feel better within a week.

You should consider seeing your GP if you're at a higher risk of becoming more seriously ill. This includes people who:

  • are 65 or over
  • are pregnant
  • have a lung, heart, kidney, liver or neurological disease
  • have a weakened immune system 
  • have diabetes

In these cases, your GP may suggest taking antiviral medication.

Managing your symptoms at home

If you're otherwise healthy, you can look after yourself at home by resting, keeping warm and drinking plenty of water to avoid dehydration.

If you feel unwell and have a fever, you can take paracetamol or anti-inflammatory medicines such as ibuprofen to lower your temperature and relieve aches. Children under 16 shouldn't be given aspirin.

Stay off work or school until you're feeling better. For most people, this will take about a week. See your GP if your symptoms get worse or last longer than a week.

Read the page on preventing flu for more information about stopping the infection spreading to others.

Antiviral medication

In 2009, the National Institute for Health and Care Excellence (NICE) recommended that doctors should consider treating people in the at-risk groups mentioned above with the antiviral medications oseltamivir (Tamiflu) or zanamivir (Relenza) to reduce the risk of complications of flu.

Antivirals work by stopping the flu virus from multiplying in the body. They won't cure flu, but they may help slightly reduce the length of the illness and relieve some of the symptoms.

Recent research has suggested that Tamiflu and Relenza may not be effective at reducing the risk of flu complications and could cause side effects, so not all doctors agree they should be used.

But there is evidence that antivirals can reduce the risk of death in patients hospitalised with flu. In the light of this evidence, Public Health England says it is important that doctors treating severely unwell patients continue to prescribe these drugs where appropriate.

For more information read the NICE guidelines on antivirals to treat influenza.


Antibiotics aren't prescribed for flu as they have no effect on viruses, although they may be prescribed if you develop a complication of flu, such as a bacterial chest infection.

Complications of flu

Complications of flu mostly affect people in high-risk groups, such as the elderly, pregnant women and those who have a long-term medical condition or weakened immune system.

This is why it's important for people in these groups to have the annual flu vaccination and consider seeing their GP if they develop symptoms of flu.

Chest infections

The most common complication of flu is a bacterial chest infection, such as bronchitis. Occasionally, this can become serious and develop into pneumonia.

A course of antibiotics usually cures a chest infection or pneumonia, but it can very occasionally become life-threatening, particularly in the frail and elderly.

Worsening of existing conditions

In some people with long-term health conditions, getting flu can make their condition worse.

For example, people with lung conditions such as asthma or chronic obstructive pulmonary disease (COPD) may find that their symptoms become more severe when they get the flu.

In people with diabetes, flu can affect blood sugar levels, potentially causing hyperglycaemia (high blood sugar) or, in people with type 1 diabetes, diabetic ketoacidosis (a dangerous condition caused by a lack of insulin in the body).

If you have type 1 diabetes or have type 2 diabetes and take insulin, it's a good idea to monitor your blood sugar level more closely while you’re feeling unwell. 

Pregnancy complications

If you get flu while you're pregnant, there's a risk that the infection could cause problems with your pregnancy.

Flu may cause you to go into premature labour (before 37 weeks of pregnancy), or it may result in your baby having a low birth weight.

Occasionally, getting flu during pregnancy can result in a miscarriage or stillbirth.

Rare complications

Less common complications of flu include:

  • tonsillitis – inflammation of the tonsils
  • otitis media – an infection of the middle ear
  • sinusitis – inflammation of the lining of the sinuses (small, air-filled cavities behind your cheekbones and forehead)
  • febrile seizures (convulsions) – a fit that can happen when a child has a fever
  • meningitis – infection in the brain and spinal cord
  • encephalitis – inflammation of the brain

Preventing flu

There are 3 main ways of preventing flu:

  • the flu vaccination
  • good hygiene (such as handwashing and cleaning)
  • antiviral medication

The flu vaccine

The annual flu vaccine can help reduce your risk of getting flu each year, although it's not 100% effective because it doesn't work against every possible type of flu virus.

With coronavirus (COVID-19) around, it is more important than ever to get the flu vaccine this autumn to protect yourself, others and the NHS.

Find out more about the flu vaccine

Good hygiene

To reduce your risk of getting flu or spreading it to other people, you should always:

  • make sure you wash your hands regularly with soap and warm water
  • clean surfaces (such as your keyboard, telephone and door handles) regularly to get rid of germs
  • use tissues to cover your mouth and nose when you cough or sneeze
  • put used tissues in a bin as soon as possible

Antiviral medication

Taking the antiviral medicines oseltamivir (Tamiflu) or zanamivir (Relenza) to prevent flu is recommended if all of the following apply:

  • there's a lot of flu around
  • you're over 65, pregnant, or have a medical condition that puts you at risk of complications of flu, such as diabetes, heart disease, lung disease, kidney disease or a neurological disease 
  • you've been in contact with someone with a flu-like illness and can start antiviral treatment within 36-48 hours
  • you haven't had the flu vaccination

If there's an outbreak of flu in a residential or nursing home – where the flu virus can often spread very quickly – antiviral medication may be offered to people if they've been in contact with someone with confirmed flu.

For more information, read the guidelines from the National Institute for Health and Care Excellence (NICE) on antivirals to prevent influenza.

Last updated:
29 May 2023