Cancer and treatments such as chemotherapy weaken the immune system and so medics will be keen for the King to avoid infection as he resumes public duties.
Charles has returned to public life as the weather is improving, meaning many events can be held outside, minimising the risk he will pick up illnesses from other people in confined spaces.
According to Macmillan Cancer Support, patients can cut their risk of infection by avoiding contact with people suffering from illnesses such as sore throats, colds, flu, diarrhoea or vomiting.
We wish His Majesty The King all the very best with his return to public-facing duties.
If you have cancer and are considering returning to work, we can help. Find support and advice on our website: https://t.co/qJHmnytB0u https://t.co/knWvS3M8UU
— Macmillan Cancer Support (@macmillancancer) April 26, 2024
Patients may also wish to avoid swimming where other people could have spread germs, and may want to stay away from crowded places during busy times.
The types of cancers which people have can also wreak havoc with their immune system.
Cancers such as lymphoma and leukaemia can prevent the body making enough white blood cells to fight infection.
Chemotherapy treatment also reduces the number of white blood cells produced by the bone marrow and can lower immunity.
This is one of the most common reasons for reduced immunity in cancer patients.
According to Macmillan, people are particularly at risk of getting an infection seven to 14 days after having chemotherapy.
After this time, their number of white blood cells will increase slowly.
Surgery can also increase the risk of infection while another cancer treatment, radiotherapy, often only has a temporary effect on the immune system.
Cancer patients may be told they can improve their chances of not picking up an infection by washing their hands regularly, including after gardening, not sharing towels and washing hands after dealing with animals.