Flu is a highly infectious and very common viral illness that is spread by coughs and sneezes.

It's not the same as the common cold. Flu is caused by a different group of viruses and symptoms tend to be more severe and last for longer.

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

Flu causes a sudden high temperature, headache and general aches and pains, tiredness and sore throat.

You can also lose your appetite, feel nauseous and have a cough.

Flu symptoms 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.

When to see a doctor

If you are otherwise fit and healthy, there is usually no need to see a doctor 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.

You should see a doctor if you have flu-like symptoms and you:

• are 65 or over
• are pregnant
• have a long-term medical condition such as diabetes, heart disease, lung disease, kidney or neurological disease
• have a weakened immune system

This is because flu can be more serious for you, and your doctor may want to prescribe antiviral medication.

Antiviral medicine can lessen the symptoms of flu and shorten its duration, but treatment needs to start soon after flu symptoms have begun in order to be effective.

Antibiotics are of no use in the treatment of flu because it is caused by a virus and not bacteria.

Read more about how to treat flu and who should see a doctor.

How long does flu last?

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

Symptoms peak after two to three days and you should begin to feel much better after a week or so, although you may feel tired for much longer.

You are usually infectious – that is able to pass on flu to others – a day before your symptoms start, and for a further five or six days. Children and people with weaker immune systems, such as cancer patients, may remain infectious for longer.

Elderly people and anyone with certain long-term medical conditions are more likely to have a bad case of flu, and are also more likely to develop a serious complication such as a chest infection.

In the UK, about 600 people a year die from a complication of seasonal flu. This rises to around 13,000 during an epidemic.

Read more about the complications of flu.

Preventing the spread of flu

The flu virus is spread in the small droplets of fluid coughed or sneezed into the air by an infected person. These droplets can travel a metre or so and infect anyone within range who breathes them in.

Flu can also spread if someone with the virus transfers it on their fingers. For example, if you have flu and you touch your nose or eyes and then touch someone else, you may pass the virus on to them. Similarly if you have flu and touch common hard surfaces such as door handles with unwashed hands then other people who touch the surface after you can pick up the infection.

Read more about the causes of flu.

You can stop yourself catching flu in the first place or spreading it to others by being careful with your hygiene. 

Always wash your hands regularly with soap and water and:

• regularly clean surfaces such as your keyboard, telephone and door handles 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

Learn more about stopping the spread of flu by watching this video about the government's Catch it, Bin it, Kill it campaign.

You can also help stop the spread of flu if you avoid all unnecessary contact with other people while you're infectious. You should stay off work until you are no longer infectious and you are feeling better.

Read more about how to stop the spread of flu.

The flu jab

A flu vaccine is available free on the NHS if you:

• are pregnant
• 65 or older
• have a serious medical condition
• are a healthcare worker or carer
• live in a residential or nursing home

Despite popular belief, the flu vaccine cannot give you flu as it doesn't contain the active virus needed to do this.

The flu vaccine is available from October each year. If you think you need it, talk to your GP or practice nurse.

For more information on who should have the flu jab and how to get it read our section on the seasonal flu jab.

Flu can give you any of these symptoms:

• sudden fever - a temperature of 38°C (100.4°F) or above
• dry, chesty cough
• headache
• tiredness
• chills
• aching muscles
• limb or joint pain
• diarrhoea or upset stomach
• sore throat
• runny or blocked nose
• sneezing
• loss of appetite
• difficulty sleeping

Your symptoms will usually peak after two to three days and you should begin to feel much better within five to eight days. However, you may have a lingering cough and still feel very tired for a further two to three weeks.

When to visit your GP

If you are otherwise fit and healthy, there is usually no need to visit 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.

You should visit your GP if you have flu-like symptoms and you:

• are 65 years of age or over
• are pregnant
• have a long-term medical condition, such as diabetes, heart disease, lung disease, kidney or neurological disease
• have a weakened immune system (the body's natural defence against infection and illness)

Flu can be more serious for these groups and antiviral medication may need to be prescribed.

Read more about how to treat flu and who should see a doctor.

The flu virus is contained in the millions of tiny droplets that come out of the nose and mouth when someone 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. And anyone who touches the surfaces the droplets have landed on can also catch flu if they pick up the virus on their hands and then touch their nose or mouth.

Everyday items at home and in public places can easily become contaminated with traces of flu virus including food, door handles, the remote control, handrails, telephone handsets and computer keyboards.

So, it's very important to wash your hands frequently to prevent catching and spreading flu.

Read more about how to prevent the spread of flu.

New types of flu

If you become infected with a flu virus your body will produce antibodies against it. Antibodies are proteins that recognise and fight off germs that have invaded your body. 

Your antibodies will remember this flu virus and fight it if it invades your body again.

But, over time the flu virus can change into a different version or strain, which means your body may not recognise it and you can catch flu again.

When the virus changes to a new strain that people have little or no resistance to, it can cause a flu pandemic, which means it can spread globally. This is what happened in the swine flu pandemic of 2009.

If you are otherwise fit and healthy, you do not need to see your GP when you have flu.

Read more about treating flu.

When you should see your GP

You should see your GP if you have flu and any of the following applies to you:

• your symptoms have got much worse and include shortness of breath, chest pain or coughing up blood, or you have developed other symptoms that are not typical of flu, such as a rash
• your symptoms have lasted for longer than a week
• you have a medical condition that is making your flu worse (see Complications)

Your GP will diagnose flu based on your symptoms and your medical history. If they suspect that your symptoms are caused by a different condition - for example, malaria, if you have recently been travelling, you may need to have further tests or a referral to a hospital specialist.

If you have flu, it will usually be possible for you to treat yourself effectively at home.

If this is the case you should:

• rest
• keep warm
• drink 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 high temperature and relieve aches.

If you are in a 'high-risk' group (see box) and are more likely to suffer complications from flu, your doctor may prescribe antiviral medication.

Antibiotics are not prescribed for flu as they have no effect on viruses. However, occasionally it may be necessary to treat complications of flu, especially serious chest infections or pneumonia, with a course of antibiotics.

Antivirals will not cure flu but they will help to:

• reduce the length of time you are ill by around one day
• relieve some of the symptoms
• reduce the potential for serious complications.

Antivirals work by stopping the virus from multiplying in your body. There are two main types:

• Tamiflu
• Relenza

Tamiflu (oseltamivir)

Tamiflu is taken by mouth (orally) in capsule or liquid form. You need to start taking Tamiflu within 48 hours of getting the first symptoms of flu.

The dose is usually one tablet twice a day for five days. However, if you have kidney disease you may be prescribed a lower dose.

Tamiflu can cause nausea, vomiting, stomach pain and diarrhoea. These side effects shouldn't be serious, but see your GP if you are worried.

Relenza (zanamivir)

Relenza is a dry powder that you breathe in through an inhaler. As with Tamiflu, you need to start taking it within 48 hours of your first flu symptoms (36 hours for children). The dose is two inhalations twice a day for five days.

It's a safe treatment that rarely has any side effects.

Antiviral medication can sometimes be taken to prevent flu.

Read more about medicines for 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.

The most common complication is a bacterial chest infection. 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.

Other serious complications are uncommon.

Rare complications

Rare complications include:

• tonsillitis
• otitis media (a build-up of fluid in the ear)
• septic shock (infection of the blood that causes a severe drop in blood pressure)
• meningitis (infection in the brain and spinal cord)
• encephalitis (inflammation of the brain).

There are three main ways of preventing flu.

• Hygiene – handwashing and cleaning
• Flu vaccination
• Antiviral medicines

Good hygiene

Preventing the spread of germs is the most effective way to slow the spread of flu. Always:

• Make sure you wash your hands regularly with soap and water.
• Clean surfaces like 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.

The flu jab

Annual flu vaccination is available free to the following high-risk people, to protect them from flu:

• people aged 65 or over
• pregnant women
• people with a serious medical condition
• people living in a residential or nursing home
• carers of people at risk of complications of the flu 
• healthcare professionals

The flu jab is available from October each year. If you think you need it, talk to your doctor or nurse. Find your local GP surgery here.

It has been recommeded that children from age 2 to 17 should also have the annual influenza vaccination. 

However, it is unlikely that the vaccine, which will be given as a nasal spray rather than an injection, will be offered before 2014. For more information read our flu vaccine for children Q&A.

Vaccination advice for pregnant women

The flu vaccine will be offered to ALL pregnant women at any stage of pregnancy.

Read more about the seasonal flu jab, including background information on the vaccine and how you can get the jab.

Antiviral medication

It is recommended that you take the antiviral medicines Relenza or Tamiflu to prevent flu if all of the following apply:

• There is a lot of flu around.
• You have a medical condition that puts you at risk of flu such as diabetes, heart disease, lung disease or kidney disease.
• You are aged 65 or over. 
• You have been in contact with someone with a flu-like illness and can start antiviral treatment within 48 hours.
• You have not been effectively protected by vaccination.

You are not effectively protected by vaccination if you:

• Have not been vaccinated since last winter.
• Cannot be vaccinated, or have been vaccinated but it hasn't taken effect yet.
• Have been vaccinated for a different form of flu virus.

If there is 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 have been in contact with someone with confirmed flu.

For more information, go to the NICE guidelines on antivirals to prevent influenza.