a crate of colourful vegetables

What is the immune system?

05 Jun 2023

It helps keeps away coughs, colds and all sorts of other bugs. Read more about how your amazing immune system actually works

Written by Charlotte Haigh on January 21, 2019 Reviewed by Professor Michael Rudenko on January 31, 2019

You probably only think about your immune system when colds and flu are doing the rounds. But it’s working all the time to guard you against foreign invaders, mounting constant attacks to defend your body without you even noticing.1

What exactly is the immune system?

It’s a huge, complex network of cells, organs, proteins, and antibodies – known as immunoglobulins – designed to prevent your body from invasion by bacteria, viruses and parasites. In fact, it saves your life on a daily basis: it’s your immune system that launches an attack when it detects something that shouldn’t be there.

Your immune system also shifts dead or faulty cells out of the body, and, if working correctly, it recognises normal, healthy tissue and leaves it alone.2

Meet your immune system’s key players

White blood cells, also called leukocytes, roam your body, monitoring the presence of pathogens – organisms which can give us diseases. White blood cells are produced and stored in the following organs:3
  • lymph nodes, spread throughout the body
  • thymus gland, in your neck
  • spleen, found above the stomach
  • bone marrow

There are two main types of white blood cells:

1. Phagocytes

These break down and eat pathogens. Phagocytes include:

  • macrophages – they patrol for foreign bodies and remove waste cells
  • neutrophils – these attack bacteria

2. Lymphocytes, or effector cells

Produced in bone marrow, lymphocytes remember previous invaders and mount an attack as soon as they detect their presence again. There are:

  • B-cells – these act as lookouts, keeping an eye out for pathogens and sending alerts
  • T-cells – they receive signals from B-cells. Helper T-cells coordinate the immune response, while natural killer T-cells destroy infected cells4

Mast cells are a separate group of cells that are important in allergy. Their job is to heal wounds, but they also release a substance called histamine that can trigger allergy symptoms.

So, what can go wrong?

Certain conditions can involve a problem with your immune system:

Allergies – these can develop when your immune system reacts to something harmless – like dust or pollen – as though it’s a pathogen, causing symptoms such as wheezing, itching and a runny nose.5

Anaphylaxis – this is a severe, life-threatening response to a particular trigger, such as a bee sting or nuts. Symptoms include sudden swelling of your mouth and throat, shortness of breath, hives, nausea and vomiting. Anapyhylaxis is a medical emergency so seek help immediately if you experience these symptoms.6

Autoimmune disorders – conditions like rheumatoid arthritis, coeliac disease, multiple sclerosis and type 1 diabetes are autoimmune disorders – a result of your immune system confusing normal, healthy cells for pathogens, then attacking and destroying them.7

Immunodeficiency – this happens when any part of your body’s immune response isn’t working correctly, leaving you exposed to infection. This can happen due to ageing, poor nutrition, alcoholism, obesity or HIV.8

Five ways to support your immune system

Although we often talk about ‘boosting immunity’, in reality it’s more about immune support and supporting your immune system to do its job well, keeping it healthy and balanced.

Five of the most important ways you can look after your immune system are:

1. Get plenty of sleep: if you miss out on sleep, your immune system can’t release enough protective proteins, called cytokines. Your production of antibodies, which fight infection, also declines.9

2. Eat a balanced diet, with lots of fruit and veg: a 2018 study in Nutrients reported that deficiencies in certain key nutrients can dampen immunity, particularly:

If you feel you’re missing any of these nutrients in your diet, it may be a good idea to take a multivitamin.10

3. Reduce stress: a 2014 study by Stanford University, USA found chronic stress can suppress your immune system’s protective effects. It can also trigger the type of immune over-reaction associated with the development of auto-immune diseases.11 Make time to unwind every day, for example with yoga, walking or meditation.

4. Don’t smoke: the tar and other chemicals in cigarettes can weaken your immune system.  Smoking also forces white blood cells to stay elevated, stressing the body.12

5. Get some exercise: being active helps strengthen your immune system. Scientists aren’t sure why, but theories include:13

  • the rise in body temperature during a workout helps kill bacteria, leaving you better able to fight infection
  • exercise may help flush bacteria out of the airways
  • being active reduces stress hormones, which can suppress immunity

And while extreme endurance exercise – such as intensive gym work or training for a marathon – may temporarily suppress the immune system, leaving you more exposed to catching a bug, it does have a plus side: a 2017 study by Shanghai University of Sport found that during high-intensity training the immune system can actually produce an anti-inflammatory effect – reducing our risk of cardiovascular conditions in later life.14

Shop Cold & Immune Support Advice is for information only and should not replace medical care. Please check with your GP before trying any remedies.


1. Tim Newman. Medical News Today. How the immune system works

2. As above
3. As Source 1
4. As Source 1

5. Johns Hopkins Medicine. Allergies and the immune system

6. As above

7. MedlinePlus. Autoimmune disorders 8. British Society for Immunology. Immunodeficiency 9. Eric J. Olson. Mayo Clinic. Lack of sleep: can it make you sick? 10. Maggini S, Pierre A, Calder PC. Immune Function and Micronutrient Requirements Change Over The Life Course 11. Dhabhar FS. Effects of stress on immune function: the good, the bad, and the beautiful 12. Smokefree.gov. Health Effects 13. MedlinePlus. Exercise and Immunity 14. Liu D, et al. Immune adaptation to chronic intense exercise training: new microarray evidence

Related Topics