Flu is an infectious and common viral illness spread by coughs and sneezes.
It's not the same as the common cold. Flu is caused by a different group of viruses. 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 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 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 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 feeling better.
Read more about how to stop the spread of flu.
The flu jab
A flu vaccine is available free on the NHS for:
- pregnant women
- children aged between two and three
- children aged 2-18 with a long-term health condition
- adults aged 65 or older
- people with a serious medical condition
- healthcare workers or carers
- people living 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.