The Queen has been forced to withdraw from her engagements and is resting at home after being diagnosed with a chest infection.
Chest infections – an infection of the lungs or large airways – are common, especially after a cold or flu during autumn and winter.
Most chest infections are mild and clear up on their own, others can be severe and sometimes even life threatening.
The most common symptoms of a chest infection include a persistent cough, wheezing, breathlessness, a high temperature, coughing up phlegm, a rapid heart rate and chest pain or tightness.
People may also experience headaches, aching muscles and tiredness.
To ease symptoms people are advised to get plenty of rest and drink lots of fluids.
They can also use painkillers to relieve headaches and muscle pain as well as to bring down a fever.
Home remedies can also include sleeping with extra pillows to make breathing easier and a hot lemon and honey drink to soothe a sore throat.
Camilla, 77, is understood to be under doctors’ supervision.
The main types of chest infections are bronchitis and pneumonia.
According to NHS Inform, most bronchitis cases are caused by viruses while most pneumonia cases are due to bacteria.
If The Queen has been diagnosed with a bacterial chest infection, then she will be treated with antibiotics.
These drugs work by killing the bacteria.
Antibiotics can be prescribed with or without steroids, which help open the airways in the lungs and make breathing easier.
For viral chest infections, antibiotics are not advised. But people with viral chest infections can be prescribed steroids.
A number of groups can be at higher risk of developing serious chest infections, these include babies and very young children, children with development problems, people who are very overweight, elderly people, pregnant women, people who smoke and people with long-term health conditions.
Queen Camilla used to be a heavy smoker – a habit her husband Charles loathed – but she gave up many years ago.
Dr Andrew Whittamore, clinical lead at the charity Asthma and Lung UK, and a practising GP, said: “A chest infection is an infection that affects your lungs or airways and symptoms include a chesty cough, wheezing or shortness of breath, a high temperature of 38 degrees Celsius or above, and chest pains or discomfort.
“While most chest infections are not serious and last around three weeks, some can develop into more serious illnesses such as pneumonia or bronchitis. They can also worsen underlying health conditions such as asthma or COPD (chronic obstructive pulmonary disease).
“Pneumonia is a type of chest infection and a leading cause of emergency hospital admissions every winter, placing significant pressures on the NHS – symptoms can include a cough, difficulty breathing, a high temperature, chest pain and loss of appetite.
“The condition, usually caused by a bacterial infection or a virus such as flu, leads to the tissue in one or both lungs to swell or become inflamed. While mild pneumonia can be treated with medication at home, in some cases, pneumonia can be life-threatening and require hospital treatment.
“Bronchitis is inflammation of the airways in the lungs that may be caused by an infection, and it often gets better in around three weeks.
Dr Whittamore added: “Young children, those aged over 65 and those with existing lung conditions such as asthma or COPD, can be more prone to chest infections. They can also be more serious among these groups because the inflammation causes narrowing of the airways making it harder to breathe.
“Also, in young children and older people it may be harder for them to get rid of mucus because their body’s defences may not be working as well in the lungs.
“It’s important to see your GP if you think you have a chest infection, especially if you have a lung condition such as asthma.”
He added: “The best way to safeguard against a chest infection is to stop smoking if you smoke, keep up to date with your vaccinations, try to prevent spread of infection by washing your hands often with warm water and soap, using tissues to trap germs when you cough or sneeze, and throwing away used tissues as quickly as possible.”