Flu 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 - short for influenza - all year round, but it's especially common in winter, which is why it's also known as "seasonal flu".
It's not 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:
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.
If you're otherwise fit and healthy, there's usually no need to see a doctor 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.
Consider visiting your GP if:
In these situations, you may need medication to treat or prevent complications of flu. Your doctor may recommend taking antiviral medicine to reduce your symptoms and help you recover more quickly.
Read more about antiviral medication for flu.
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 will usually be most infectious from the day your symptoms start and for a further three to seven 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.
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 natural resistance to the new versions.
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:
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 (see below) or antiviral medication may be recommended to help reduce the risk of becoming infected.
Read more about how to stop the spread of flu.
A flu vaccine is available for free on the NHS for:
An annual flu vaccine nasal spray is also now offered to healthy children aged two, three and four years old, and to children in school years one and two.
The best time to have the vaccine is in the autumn, between September and early November. If you think you might need it, contact your local GP surgery.
You should have the flu vaccination every year so you stay protected, as the viruses that cause flu change every year.
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