A cough is a reflex action to clear your airways of mucus and irritants such as dust or smoke.

Coughs may be dry or chesty (see box below). They're also classified according to how long they last:

• acute cough lasts for less than three weeks 
• subacute cough gets better over a three-to-eight-week period 
• chronic (persistent) cough lasts for longer than eight weeks

Coughs caused by the common cold or by flu usually clear up after several days. Most coughs clear up within two weeks.

For more information on treating cough, go to Treatment.

What are the causes?

Most people with a cough have a respiratory tract infection caused by a virus, such as the common cold, flu or bronchitis.

A persistent cough in adults may be caused by a condition such as rhinitis, or by a prescribed medicine such as an angiotensin-converting enzyme (ACE)-inhibitor, which is used to treat high blood pressure or cardiovascular disease, or by smoking.

In children, a persistent cough may indicate a more serious respiratory tract infection such as whooping cough.

For more information on conditions that cause cough, go to Causes of cough.

When to see your doctor

See your GP if you've had a cough for more than two weeks after a viral infection, or if your cough is progressively getting worse.

Most coughs are caused by viral infections and usually clear up on their own.

Acute cough

Most people with an acute cough have a respiratory tract infection caused by a virus.

It will usually be an upper respiratory tract infection (URTI), which means the virus has affected your throat or windpipe. Examples of URTIs causing cough are:

• the common cold 
• influenza (flu) 
• laryngitis

If your cough is caused by a lower respiratory tract infection (LRTI), the virus has infected your airways lower down, or your lungs. Examples of LRTIs are:

• bronchitis 
• pneumonia (although this is rare) 

Other possible causes for an acute cough are allergic rhinitis, such as hay fever. In rare cases it may be the first sign of a chronic disease (see below).

Chronic cough

Common causes of a persistent cough in adults are:

• smoking
• postnasal drip (mucus dripping down the throat from the back of the nose, caused by a condition such as rhinitis)
• gastro-oesophageal reflux disease

Some prescribed medicines can also cause a persistent cough (for example, angiotensin-converting enzyme [ACE]-inhibitors, which are medicines for treating high blood pressure or cardiovascular disease).

In children, common causes are:

• respiratory tract infections, such as bronchitis or whooping cough 
• gastro-oesophageal reflux disease

Rarely, a cough is a symptom of a more serious condition such as lung cancer, heart failure, a pulmonary embolism (clot on the lung), cystic fibrosis or tuberculosis (TB).

How long a cough lasts for depends on the cause. If it has been caused by the common cold, it can clear up after two to three days. Most coughs clear up within two weeks.

A dry cough will feel like a constant tickle in your throat. When you cough, there won't be any phlegm (thick mucus).

If you have a chesty cough as a result of a respiratory infection, you may cough up phlegm.

If you have a cough due to a viral infection, such as flu or bronchitis, you won't usually need to see a doctor unless your symptoms are severe.

When to see your doctor

See your GP if your cough has lasted for more than two weeks or is getting progressively worse.

Occasionally, a secondary bacterial infection occurs, which can lead to a more serious condition developing, such as pneumonia.

Typical symptoms of pneumonia include rapid and shallow breathing, wheezing and coughing up phlegm that may be yellow, green, brownish or blood-stained.

Coughs caused by the common cold or by flu usually clear up after several days, so you won't have to see your GP.

If you've had a cough for more than two weeks after a viral infection, seek medical advice from your GP.

Your GP will take your medical history, do a full clinical examination and sometimes take some tests.

Tests

Your GP may do a chest X-ray to see if you have a chest infection and, if there is an infection, to determine the extent of it.

If you have a chesty cough, a sample of your coughed-up phlegm may be taken for analysis in a laboratory, to determine which germ has caused the infection. This information can then be used to decide whether or not antibiotics should be used to treat it (see Treatment of coughs).

Spirometry may be used to see if you have an underlying respiratory condition. It involves breathing in and out of a tube connected to a machine, so that your GP can assess whether or not your airways have narrowed.

You may have allergy testing, such as a skin prick test, to see whether your cough is caused by something you're allergic to, such as house dust mites.

Referral

If your GP is unsure what's causing your cough or your cough is getting worse, they may refer you to a respiratory specialist.

Antibiotics

Antibiotics are medicines that can be used to treat infections caused by micro-organisms, usually bacteria or fungi. For example amoxicillin, streptomycin and erythromycin.

Inflammation

Inflammation is the body's response to infection, irritation or injury, which causes redness, swelling, pain and sometimes a feeling of heat in the affected area.

X-ray

An X-ray is a painless way of producing pictures of inside the body using radiation.

There's no quick way of getting rid of a cough that's caused by a viral infection. It will usually clear up after your immune system has fought off the virus.

The simplest and cheapest way to treat a short-term cough may be a homemade cough remedy containing honey and lemon. The honey is a demulcent, which means it coats the throat and relieves the irritation that causes coughing.

Cough medicines

There's little evidence to suggest that cough medicines actually work, although some of the ingredients may help to treat symptoms that are associated with a cough, such as a blocked nose or fever.

Some contain paracetamol, so don't take more than the recommended dosage. Cough medicines should never be taken for more than two weeks.

They can be used for any type of cough and are generally safe, but diabetics should note that they're usually sugar-based.

Treating children

The Medicines and Healthcare products Regulatory Agency (MHRA) has recommended that over-the-counter cough and cold medicines shouldn't be given to children under the age of six.

The MHRA is the government body responsible for ensuring that medicines are safe and effective.

The agency has made this recommendation because it feels there's a potential risk of these medicines causing unpleasant side effects, such as allergic reactions, sleep problems or hallucinations (seeing and hearing things that aren't real). These would outweigh any benefit provided by the medicines.

Instead, give your child a warm drink of lemon and honey or a simple cough syrup that contains glycerol or honey.

However, honey shouldn't be given to babies under the age of one, due to the risk of infant botulism.

For more information, see News: child cold medicines Q&A.

Cough suppressants

Cough suppressants, such as pholcodine, dextromethorphan and antihistamines, act on the brain to hold back the cough reflex. They're used for dry coughs only.

• Pholcodine and dextromethorphan have few side effects or interactions with other medicines.
• Antihistamines sometimes cause drowsiness, which can be helpful if your cough is disrupting your sleep. Other possible side effects are a dry mouth, constipation, difficulty in passing urine and blurred vision. Antihistamines might interact with other medicines, such as antidepressants and those that cause drowsiness.

Check with your GP or pharmacist before taking cough suppressants.

Expectorants

Expectorants help bring phlegm up so that coughing is easier, which may help chesty coughs. They include:

• guaiphenesin
• ammonium chloride
• squill
• sodium citrate
• ipecacuanha

These compounds are all found in small quantities in cough mixtures, so they're unlikely to have any side effects or interact with other medicines.

Antibiotics

Antibiotics are medicines that can be used to treat infections caused by micro-organisms, usually bacteria or fungi. For example amoxicillin, streptomycin and erythromycin.

Antidepressants

Antidepressant medicine is used to treat depression. For example Fluoxetine, Paroxetine.

Antihistamines

Antihistamine medicine counteracts the action of histamine (a chemical released during an allergic reaction). For example loratadine, hydroxyzine.

Bacteria

Bacteria are tiny, single-celled organisms that live in the body. Some can cause illness and disease and some others are good for you.

Congestion

Congestion is an excess of fluid in part of the body, often causing a blockage.

Decongestant

Decongestant medicine relieves congestion by reducing the swelling of the lining the nose and sinuses and drying up the mucous.

Expectorants

Expectorant medicine helps you to cough up phlegm.

Fever

A high temperature, also known as a fever, is when someone's body temperature goes above the normal 37ºC (98.6ºF).

Immune system

The immune system is the body's defence system, which helps protect it from disease, bacteria and viruses.