Cancer and its treatments can weaken the immune system. It is important to try and avoid infection if your immunity is reduced.

What is infection?

You might get an infection if harmful organisms such as bacteria and viruses enter the body. Your body’s immune system usually helps protect you from infection. But cancer and its treatment can stop the immune system from working properly.

Infections can usually be treated with antibiotics. If an infection is not treated quickly, it can be much more difficult to get it under control.

Sepsis (also called blood poisoning) is a serious and potentially life-threatening complication of an infection. We have more information about sepsis, contacting your hospital team, and protecting yourself.

It is important to follow any advice your cancer treatment team gives you. Contact the hospital straight away on the number you have been given if:

  • you develop a high temperature, which may be over 37.5˚C (99.5˚F)
  • you suddenly feel unwell, even with a normal temperature
  • you have symptoms of an infection.

Symptoms of an infection include:

  • feeling shivery
  • a sore throat
  • a cough
  • diarrhoea
  • needing to pass urine often.

How does the immune system work?

The immune system is the body's defence against bacteria, viruses and other foreign organisms or harmful chemicals.

The immune system has three parts:

  • the skin and mucous membranes
  • proteins produced by the body
  • blood and lymph cells.

The skin and mucous membranes

The skin protects our body and internal organs from infection. The mucous membranes also act as a protective barrier to stop germs getting into your body. They are in areas of the body that are more open to germs, such as the:

  • mouth
  • nose
  • digestive system
  • urethra (the tube that urine passes out of).


There are special proteins and chemicals in the fluids your body produces. If organisms get into your body, the proteins attack them.

Blood and lymph cells

Blood and lymph cells are produced by the bone marrow and the lymphatic system. The bone marrow is the spongy material in the middle of some of our bones. The lymphatic system is a system made up of organs such as the:

  • lymph nodes
  • thymus
  • spleen, which contains white blood cells that fight infection.

Different types of white blood cells work to destroy organisms that get into the body. They travel through your blood or lymphatic vessels to the area of damage or infection. Then they destroy the harmful organisms.

The lymphatic system full body

How cancer and treatments may affect the immune system

Cancer and its treatment can affect the immune system in different ways.

The type of cancer you have

Some cancers, particularly lymphomas and leukaemias, can prevent the body's immune system from working properly. For example, they may do this by preventing the bone marrow from producing enough healthy white blood cells.

The type of cancer treatment you have


Chemotherapy reduces the number of white blood cells produced by the bone marrow. This can have a big effect on the immune system. It reduces your body's defences against infection during and after treatment. Chemotherapy treatment is usually the most common reason for reduced immunity.

You are particularly at risk of getting an infection 7 to 14 days after having chemotherapy, when the level of white blood cells is at its lowest. This time is called the nadir. It can vary slightly depending on the drugs used.

The number of white blood cells will increase steadily and usually returns to normal before your next cycle of chemotherapy.

You will have your blood checked before you have more chemotherapy, to make sure the white cells are at a normal level. Your chemotherapy nurse will give you more information.


Surgery can make you more at risk of infection. This is because it makes a break in the skin or in the mucous membranes, which both help protect the body from infection.

If the operation involves removing the spleen, infection is much more likely. The spleen is an important part of the immune system. It contains white blood cells that fight infection and gets rid of old red blood cells. Having your spleen removed means that your immunity is permanently affected. Your doctor will advise you to take low-dose antibiotics for the rest of your life, to protect your from infection.


Radiotherapy usually only has a mild and temporary effect on the immune system. It is unlikely to cause any problems.

But some people will have radiotherapy to the whole body (total body irradiation). For this, all of the bone marrow gets a dose of radiation, so the person will be at risk of infection for some time afterwards. This type of radiotherapy may be used for people who are having a bone marrow or stem cell transplant.

Tips for avoiding infection

Below are some general tips to help you to reduce your risk of getting an infection when your immunity is reduced. Your cancer doctor or specialist nurse will give you more advice.


One of the best ways to avoid infection is having good personal hygiene. You can do this by doing the following:

  • Wash your hands regularly with soap and hot water.
  • Always wash your hands after you have been to the toilet.
  • Always wash your hands before you prepare or eat food.
  • Have a daily shower or bath, but do not share towels or flannels with anyone else because there is a risk of infection.

Contact with others

You can avoid infection by being careful about your contact with others. You can do this by doing the following:

  • Avoid people with obvious infections

    Stay away from people with sore throats, colds, flu, diarrhoea or vomiting, or infections such as chickenpox. If you are in contact with anyone who has an obvious infection, ask your hospital doctor or specialist nurse for advice as soon as possible. You may need to take medicines to stop you from getting the infection.

  • Avoid crowded places and public transport

    Stay away from crowded places where there are likely to be people with infections. This means avoiding public transport during rush hour and crowded shopping centres. This does not mean you should not go out, but try to avoid the busiest times.

  • Avoid swimming

    Avoid swimming or using a public pool or spa where there is a risk of picking up an infection from the water or in the changing room. If you are doing sports or social activities, try to go at quieter times.

  • Wash your hands after touching animals

    If you have pets or work with animals, you need to be extra careful. It is usually safe to touch or stroke animals, as long as you wash your hands thoroughly afterwards. Avoid handling any animal waste, such as litter trays or manure.

  • Ask to make adjustments at work

    If you aim to keep working during your treatment, talk to your employer or the HR department. They can give you support and look at making adjustments to help you avoid getting an infection. This could include working part-time or working from home when your immunity is reduced.

Mould and fungus

Avoid places where there is likely to be a mould or fungus called aspergillus. It can grow in dead leaves, grain stores, compost piles or other decaying vegetation. Aspergillus may also be found in building materials such as brick, mortar and cement dust. So it might also be in building sites. If you are worried about this, talk to your cancer doctor or specialist nurse.


Vaccinations can reduce your risk of getting certain infections. If you are planning to have any vaccinations, it is always best to discuss this with your cancer doctor or specialist nurse. If you are having cancer treatment, you may not be able to have some vaccinations.

Your doctor or nurse may talk to you about having a flu vaccination and a coronavirus vaccination. These are both inactivated vaccines that can help reduce the risk of infection. As they are not live vaccines, they cannot harm you when your immunity is reduced.

You will need to avoid live vaccines if your immune system is weak. Live vaccines include shingles, measles, mumps, rubella (MMR), oral typhoid, BCG and yellow fever. Live vaccines contain a very weak version of the illness they are vaccinating you against. If your immune system is weak, you may become unwell.

If you are planning a holiday abroad and need certain vaccinations before you travel, check with your cancer doctor or specialist nurse first.

Central lines and PICC lines

Some people having cancer treatment have central lines or PICC lines. These are long, hollow tubes made of plastic.

These lines can stay in place for many months. Your nurse will show you how to clean the line, and protect it from bacteria and possible damage.

Mouth care

You can develop a mouth infection when your immunity is low. It is important to take extra care to keep your mouth clean. Use a soft-bristled toothbrush if your gums are sore. Check inside your mouth once a day for any signs of:

  • redness
  • swelling
  • ulcers
  • white patches
  • bleeding.

Your nurse at the hospital can show you how to do this.

Your doctor may prescribe antiseptic mouthwashes for you to use after meals and at night. Sometimes they may also prescribe antifungal tablets, mouthwashes or lozenges. These can help prevent infection from developing when they are used regularly.

Because of your risk of infection, it is important not to have any dental work done without discussing it with your cancer doctor first.

Eating and drinking

Drinking plenty of fluids can help prevent infection. Fluids help keep your mouth moist and healthy. Drinking plenty of fluids also flushes out your kidneys and bladder, which helps prevent bacteria from growing.

People may find it difficult to eat and drink for different reasons. This may be due to the side effects of treatment or the cancer itself. For example, you may feel sick or have taste changes that affect your appetite. But it is important to try to eat a healthy and balanced diet, as this helps your immune system.

Some foods can have harmful bacteria in them, especially shellfish, poultry and eggs. You can reduce the risk of harmful bacteria in your food by:

  • storing food at the correct temperature and cooking it thoroughly
  • not reheating food that has cooled, as this may allow bacteria to grow again
  • using all your food before its use by date
  • keeping raw and cooked foods apart
  • always washing salads, fruits and vegetables thoroughly.

You may also be told to peel fruit before eating it.

If you have had an autologous stem cell transplant or if you have leukaemia and are having high doses of chemotherapy, you may be given diet guidelines to follow.