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.
Some of the main symptoms of flu include:
- a high temperature (fever) of 38C (100.4F) or above
- tiredness and weakness
- a 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 guideIf you have a flu-like illness, complete our self-help guide to assess your symptoms and find out what to do next.
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.
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