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.
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.
Consider visiting your doctor 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.
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.
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.
A flu vaccine is available for free on the NHS for:
An annual flu vaccine nasal spray is also offered to healthy children aged two and three, and to children in reception class and school years one, two, three and four.
The best time to have the vaccine is in the autumn, from the beginning of October to early November. If you think you might need it, contact your local doctor surgery.
You should have the flu vaccination every year so you stay protected, as the viruses that cause flu change every year.
For more information on who should have the flu vaccine and how to get it, read the sections on the flu jab for adults, the flu jab for pregnant women and the children's flu vaccine.
The symptoms of flu usually develop within one to three 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.
Flu can give you any of the following symptoms:
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:
If you are otherwise fit and healthy, there's usually no need to visit your doctor 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 doctor if:
In these situations, you may need extra treatment to prevent or treat complications of flu.
Usually, you can manage flu symptoms yourself at home and there's no need to see a doctor. Most people feel better within a week.
You should consider seeing your doctor if you're at a higher risk of becoming more seriously ill. This includes people who:
In these cases, your doctor may suggest taking antiviral medication.
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 doctor if your symptoms get worse or last longer than a week.
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 or those at risk of being severely unwell continue to prescribe these drugs where appropriate.
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.
There are three main ways of preventing flu: the flu vaccination, good hygiene (such as handwashing and cleaning) and antiviral medication.
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.
A flu vaccine is available for free on the NHS for:
Adults over 18 and children aged six months to less than two years in these groups are given an annual injection, while children aged two to 17 are given an annual nasal spray.
The annual nasal spray is also given to children aged two and three, and to children in reception class and school years one, two, three and four.
The best time to have the vaccine is in the autumn, from the beginning of October to early November. If you think you need it, contact your local doctor surgery or local pharmacy.
You should have the flu vaccination every year so you stay protected. The viruses that cause flu change every year, so this winter's flu will be different from last winter's.
Read more about:
To reduce your risk of getting flu or spreading it to other people, you should always:
Taking the antiviral medicines oseltamivir (Tamiflu) or zanamivir (Relenza) to prevent flu is recommended if all of the following apply:
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 have been in contact with someone with confirmed 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 doctor if they develop symptoms of flu.
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.
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.
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.
Less common complications of flu include:
Click on the links above for more information about the symptoms of these conditions and to find out how they're treated.
Important: Our website provides useful information but is not a substitute for medical advice. You should always seek the advice of your doctor when making decisions about your health.