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 protects you from infection. But cancer and cancer treatment can stop the immune system from working properly.

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

Sepsis is blood poisoning. It is a serious and potentially life-threatening complication of an infection.

Contact the hospital straight away on the number you have been given if:

  • your temperature goes over 37.5˚C (99.5˚F)
  • you suddenly feel unwell, even with a normal temperature
  • you have symptoms of an infection
  • your temperature goes below 36°C (96.8°F).

Symptoms of an infection

Symptoms of an infection include:

  • feeling shivery
  • a sore throat
  • a cough
  • diarrhoea
  • needing to pass urine (pee) a lot, or discomfort when you pass urine.

It is important to follow any specific advice your cancer treatment team gives you.

How does the immune system work?

The immune system help to protect us from infection and disease. It has different parts:

  • the skin and mucous membranes
  • proteins produced by the body
  • organs and 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. Mucous membranes 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).


Your body produces fluids that contain special proteins and chemicals. 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 white blood cells 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
Image: The lymphatic system

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, such as lymphomas and leukaemias, can prevent the body's immune system from working properly. For example, the cancer may stop the bone marrow 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 is one of the most common reasons for reduced immunity.

You are particularly at risk of getting an infection 7 to 14 days after having chemotherapy. This is 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.

After the nadir, the number of white blood cells will increase steadily. It should return 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. It makes a break in the skin or in the mucous membranes, which both protect the body from infection.

The spleen is an important part of the immune system. It contains white blood cells that fight infection and get rid of old red blood cells.

Surgery to remove the spleen can increase the risk of infection.

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 you from infection.


Radiotherapy usually only has a mild and temporary effect on the immune system. But some people will have radiotherapy to the whole body. This is called total body irradiation. This means that all of the bone marrow also gets a dose of radiation.

This type of radiotherapy may be used for people who are having a bone marrow or stem cell transplant. The person will be at risk of infection for some time afterwards.

Ask your doctor or radiologist for more information about your risk of infection.

Other cancer drugs

Other treatments such as targeted therapies, immunotherapy or hormonal therapies are less likely to affect your white blood cells than chemotherapy.

But some of these drugs may reduce the number of white blood cells and mean you are at increased risk of infection.

Tell your doctor or nurse if you have any signs of infection.

Tips for avoiding infection

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


One of the best ways to avoid infection is with good personal hygiene. You should:

  • 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 cooking or eating
  • always wash your hands after working in a garden
  • clean your hands with hand gel, if you are not able to wash them
  • have a shower or bath every day
  • not share towels or flannels.

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

Contact with others

You can lower your risk of infection by being careful around other people. You should:

  • Avoid people with infections

    Stay away from people with sore throats, colds, flu, diarrhoea, vomiting or infections.

  • Avoid crowded places and public transport

    Stay away from crowded places where there may be people with infections. You should avoid 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. You may choose to wear a mask or face covering to protect yourself.

  • Ask to make reasonable 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 protect you. This could include working part-time or working from home when your immunity is reduced.

  • Avoid swimming

    Avoid swimming or using a public pool or spa. There may be a risk of infection from the water or in the changing room. If you are doing sports or social activities, try to go at quieter times. 

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.

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
  • 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, thin 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:

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

Your doctor may prescribe antiseptic mouthwashes for you. Sometimes they may also prescribe antifungal tablets, mouthwashes or lozenges. If you use these regularly, they can help prevent infection.

It is important not to have any dental work done without talking to your cancer doctor first.

Eating and drinking

Drink plenty of fluids to 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 should:

  • store food at the correct temperature and cook it well
  • not reheat food
  • check ‘use by’ dates
  • keep raw and cooked foods apart
  • wash salads, fruits and vegetables
  • avoid unpasteurised milk, cheese and dairy products.

If you have had an autologous stem cell transplant or if you are having high doses of chemotherapy, your nurse may advise you about what to eat and what to avoid.

About our information

  • References

    Below is a sample of the sources used in our chemotherapy information. If you would like more information about the sources we use, please contact us at

    Brighton, D. Wood, M. The Royal Marsden Hospital Handbook of Cancer Chemotherapy. Elsevier Churchill Livingstone. 2005.

    National Institute for Health and Care Excellence (NICE) Neutropenic Sepsis Guideline CG151. 2012.

    Perry, MC. The Chemotherapy Source Book (5th ed.) Philadelphia: Lippincott, Williams & Wilkins. 2012.

    UKONS Acute Oncology Initial Management Guidelines Version 3, March 2018. Available from (accessed June 2021).

  • Reviewers

    This information has been written, revised and edited by Macmillan Cancer Support’s Cancer Information Development team. It has been reviewed by expert medical and health professionals and people living with cancer. It has been approved by Chief Medical Editor, Professor Tim Iveson, Consultant Medical Oncologist.

    Our cancer information has been awarded the PIF TICK. Created by the Patient Information Forum, this quality mark shows we meet PIF’s 10 criteria for trustworthy health information.

The language we use

We want everyone affected by cancer to feel our information is written for them.

We want our information to be as clear as possible. To do this, we try to:

  • use plain English
  • explain medical words
  • use short sentences
  • use illustrations to explain text
  • structure the information clearly
  • make sure important points are clear.

We use gender-inclusive language and talk to our readers as ‘you’ so that everyone feels included. Where clinically necessary we use the terms ‘men’ and ‘women’ or ‘male’ and ‘female’. For example, we do so when talking about parts of the body or mentioning statistics or research about who is affected.

You can read more about how we produce our information here.

Date reviewed

Reviewed: 01 March 2022
Next review: 01 March 2025
Trusted Information Creator - Patient Information Forum
Trusted Information Creator - Patient Information Forum

Our cancer information meets the PIF TICK quality mark.

This means it is easy to use, up-to-date and based on the latest evidence. Learn more about how we produce our information.