- When a person coughs, there is a short intake of breath and the larynx (the voice box) closes momentarily. The abdominal and chest muscles used for breathing contract, which in turn increases the pressure needed to drive air out the lungs when the larynx re-opens.
- The resulting blast of air comes out at high speed, scrubbing and clearing the airway of dust, dirt or excessive secretions. Coughing is a common symptom when the airways are 'tight', as in asthma.
- The cough reflex is a vital part of the body's defence mechanisms. Normally, the lungs and the lower respiratory passages are sterile. If dust or dirt get into the lungs, they could become a breeding ground for bacteria and cause pneumonia or infection in the breathing tubes.
What causes coughing?
Coughing usually means there is something in the respiratory passages that should not be there.
It could also be a sign that an infection in the lungs is making the respiratory passages produce phlegm.
Coughing can be provoked by:
- the common cold, which is a frequent cause of acute cough that usually settles in less than three weeks.
- sucking material into the breathing tubes from your mouth.
- more severe illnesses, such as pneumonia, acute heart failure or pulmonary embolism (a clot in the blood vessels of the lung).
- smoking, which often causes chronic cough (smoker's lung).
- asthma – particularly in children who may only cough and show no wheezing.
- stomach acid coming back up the gullet and spilling over into the windpipe (gastro-oesophageal reflux).
- medicines used in heart disease called ACE inhibitors.
- bacterial or viral infections in the lungs, eg acute bronchitis, pneumonia, whooping cough, croup in children
- rarely coughing can be provoked by psychological illness
- damage to the nerves that supply the vocal chords (known as vocal chordpalsy) and chronic cough can occur.
Coughing is more efficient when preceded by a full intake of air.
For this reason, patients with weak muscles, poor coordination of airway closure and re-opening, or who have airflow obstruction (as in COPD) will have a poor cough and be susceptible to complications including infection in the lower respiratory tract and pneumonia.
How can coughing be treated?
Coughing is a symptom, not a disease. It is the underlying cause of the cough that needs to be treated.
You should consult your doctor if any of the following symptoms accompany a cough, so that possible underlying causes can be investigated and treated where necessary:
- coughing up phlegm that is green, rusty brown, yellow, blood-stained or foul smelling
- chest pain
- shortness of breath or wheezing
- pain and swelling in the calf
- recurrent night-time cough
- whooping cough or croup
- worsening smoker’s cough
- sudden weight loss
- fever and sweating
- hoarseness of the voice with a chronic cough that doesn’t clear up spontaneously.
If you can't cough but need to, problems soon arise. Equally, when coughing is painful (for example, because of a broken rib), patients try not to cough and this can be dangerous.
Ineffective clearance of the airway can lead to a chest infection and possible pneumonia. In these circumstances, pain-relieving medicine can be useful to permit an efficient cough.
- Infections in the breathing tubes can be caused by both bacteria and viruses, although the most common cause in children is a virus. Bacterial infections can be treated with antibiotics, but viral infections cannot.
- Vaccination has greatly diminished the incidence of whooping cough (pertussis), but if this is the diagnosis, antibiotic treatment with a macrolide antibiotic such as erythromycin decreases the severity of this illness within the first week of treatment.
- Asthma may cause coughing without wheeziness. This tends to be worst through the night, disturbing sleep. It may be the first sign of asthma in children, or a warning sign that asthma is worsening or not controlled properly. Conventional asthma treatment with inhaled anti-inflammatory preventative medicines and relievers will usually relieve a cough that is due to asthma.
- However, a metered-dose inhaler may itself induce cough, and you may need to use a large volume spacer device or a dry powder inhaler instead.
- Gastro-oesophageal reflux requires treatment with antacids to neutralise the stomach acid, or H2 antagonists or proton-pump inhibitors to reduce the production of stomach acid.
- Giving up cigarettes will lessen or abolish smokers' cough in 94 per cent of people within four weeks.
- If an ACE inhibitor is the cause of coughing, switching to alternate treatment such as an angiotensin II receptor antagonist will help.
How effective are cough medicines?
- In cases where a cough is particularly annoying, but not life-threatening, a simple cough mixture may be useful. There are a range of over-the-counter medicines that can be helpful in such circumstances.
- Taking these can be justified when there is no special reason to suspect any serious underlying disease, such as the symptoms listed above. You should ask your pharmacist for advice on which of the many available over-the-counter cough remedies are suitable for you.
- A productive, chesty cough, in which phlegm is coughed up, should be treated with an expectorant cough mixture to help loosen the phlegm and make it easier to cough up from the airways. Expectorants contain ingredients such as guaifenesin, ipecachuana or ammonium citrate.
- A non-productive, dry, tickly or irritating cough, in which no phlegm is coughed up can, be treated with a cough suppressant to reduce the cough reflex.
- Cough suppressants include pholcodine, dextromethorphan and codeine. Other cough suppressants include simple linctus, glycerin and lemon and honey, which coat and soothe the back of the throat.
Antihistamines, such as diphenhydramine and promethazine, reduce the cough reflex and also dry up nasal secretions, which can be useful for coughs that are caused by a postnasal drip (mucus running down the back of the throat), or are associated with a cold.
Ipratropium bromide nasal spray also reduces watery nasal secretions that can cause postnasal drip and contribute to a cough.
Some cough remedies also contain sympathomimetics such as ephedrine, for their airway relaxing and decongestant effects, and can be useful if you have a blocked nose as well as a cough.
Patients should not treat themselves with cough mixture for any longer than two weeks. If the cough persists, a visit to the doctor is definitely required – informed medical assessment will help identify the underlying cause and allow treatment.
What if a young child has a cough?
Older children and adults usually have some idea whether their cough is caused by a foreign body, dust or smoke particles, or an infection in the breathing tubes. Clinical inspection will reveal features that may suggest a specific cause.
If a young child coughs, parents need to be able to tell whether the cough is a sign of disease or whether their child has a foreign body in their respiratory passages.
- If your child also has a fever or a cold, the cough is a sign of an infection. If nothing else seems to be wrong, wait for the cough to go away. If the coughing goes on for more than a couple of days, consult a doctor.
- In the meantime, if you want to give your child a medicine to help soothe the cough, it is best to use a simple cough syrup containing glycerol, honey or lemon. Other over-the-counter cough and cold remedies are no longer recommended for children under six years of age, because there is no evidence that they work and they can potentially cause side effects, such as allergic reactions, effects on sleep or hallucinations. For children over six years of age other cough and cold medicines are still available from pharmacies - ask your pharmacist for advice. Any medicine you give should be administered carefully using the spoon or measuring device supplied to ensure the maximum dose is not exceeded.
- You should avoid using more than one cough and cold medicine at the same time when treating your child's symptoms. Different medicines may contain the same active ingredient(s) and using more than one may lead to you exceeding the maximum recommended dose(s). Ask your pharmacist for more advice.
- If the coughing comes on suddenly, and is very forceful, it's likely your child has swallowed something that's causing the cough. This could be life-threatening for your child, who could choke. Lift your child by the legs so their head points downwards, then slap their back with a cupped hand. If this doesn't help, call an ambulance immediately.
- If at any point your child seems very ill, you should consult an emergency doctor immediately.
Diagnostic testing for chronic cough
If you suffer from a chronic cough, tests will need to be carried out to determine the cause.
- After initial assessment, a chest X-ray is taken to ensure that serious diseases such as lung cancer or tuberculosis (TB) are unlikely.
- Blood and skin tests are of little help, although they may reveal an allergic tendency.
- Sputum (phlegm) examination for bacteria, TB and cancer cells can be ordered, together with non-invasive heart tests such as an ECG or even echocardiography.
- In difficult cases, further tests can be considered, including fibre optic bronchoscopy, CT examination of the chest and sinuses and even methacholine inhalation challenge or oesophageal pH monitoring. These are only available in special centres.
- Whether a particular factor is responsible for chronic coughing can be determined when treatment for a specific cause achieves some benefit for the patient.
But often there is more than one cause for the cough, in which case treating only one factor will not succeed in completely relieving the symptoms. This is frustrating for both you and your medical adviser.
In such a case, a progressive and incremental approach is appropriate. Treatment directed at a specific cause is started and the result assessed.
If there is a partial but incomplete response, other treatments are then tried in turn. Eventually, the vast majority of coughing can be successfully managed in this manner.
If treatment is fruitless with no realistic chance of working – for example in the case of advanced lung cancer, the use of powerful cough suppressants may be justified.