Healthdirect Free Australian health advice you can count on.

Medical problem? Call 1800 022 222. If you need urgent medical help, call triple zero immediately

healthdirect Australia is a free service where you can talk to a nurse or doctor who can help you know what to do.

beginning of content

Immune system

5-minute read

Key facts

  • The immune system defends the body from infection and includes a complex network of cells, chemicals, tissues and organs.
  • The immune system recognises ‘invaders’ such as bacteria, viruses and fungi as well as abnormal cells like cancer cells, and then helps the body fight the invasion.
  • The immune system includes the skin, bone marrow, the thymus, lymphatic system, lymph nodes, the spleen and mucous membranes.
  • There are many different immune conditions, sometimes related to underactivity or overactivity of the immune system.

What is the immune system?

The immune system defends the body from infection. It contains a complex network of cells, chemicals, tissues and organs. An underactive or overactive immune system can cause health problems.

The immune system’s job is to protect the body from infection. It recognises ‘invaders’ such as bacteria, viruses and fungi and abnormal cells like cancer cells. It creates an immune response and helps the body fight the invasion.

When harmful germs enter and invade the body, the body produces white blood cells to fight the infection. The white blood cells identify the germ and produce antibodies to fight it. Antibodies are proteins produced by the immune system that fight germs that cause disease. White blood cells also help with other immune responses, and can 'remember' the attack they have launched.

‘Remembering’ the attack is important when the body is exposed to the same germ in the future. It is also important for understanding how vaccines work. Vaccines expose the immune system to a dead or weakened germ, or to proteins from a germ. The body can recognise and respond very quickly to any future exposure to the same germ.

What are the parts of my immune system?

The immune system involves many parts of your body. Each part plays a role in recognising germs, communicating with other body parts, and working to fight the infection. Parts of the immune system include your skin, bone marrow, thymus, lymphatic system, lymph nodes, spleen and mucous membranes.

How does my immune system work?

Each part of your immune system works in different ways.

  • Skin is the first line of defence, and helps keep germs out of your body.
  • Bone marrow helps produce immune cells.
  • The thymus is a gland in the upper chest where some immune cells mature.
  • The lymphatic system is a network of tiny vessels that allow immune cells to travel between tissues and the bloodstream. The lymphatic system contains lymphocytes (white blood cells; mostly T cells and B cells). Lymphocytes try to recognise any bacteria, viruses or other foreign substances in the body and fight them. They are carried in a milky fluid called lymph.
  • Lymph nodes are small lumps of body tissue in the groin, armpit, around the neck and elsewhere that help the lymphatic system to communicate. They can become swollen when the body has an immune response.
  • The spleen, is an organ under your ribs on your left side that processes information from the blood.
  • Mucous membranes, like the lining of the inside of your mouth and nose, trap germs and allow your immune cells to catch and attack them.
Illustration showing the various organs of the immune system.
The various organs of the immune system.

What immune conditions are there?

There are many different immune conditions. Some are due to underactivity or overactivity of the immune system.

An overactive immune system is related to disorders such as allergies and autoimmune diseases:

  • Allergies involve an immune response to something considered harmless for most people, such as pollen or a certain food.
  • Autoimmune diseases, such as multiple sclerosis and rheumatoid arthritis, happen when the immune system attacks normal, healthy parts of your body.

An underactive immune system, or immunodeficiency, can increase your risk of infection. If you have immunodeficiency, your body doesn’t fight infection as it should. You may be born with an immunodeficiency (known as primary immunodeficiency (PID), or get it from a medical treatment or another disease (known as secondary immunodeficiency).

Visit the Immune Deficiencies Foundation Australia (IDFA) website for more information about immunodeficiency.

What are some of the symptoms of immune conditions?

If you have an immunodeficiency, you may have some of the following symptoms:

If you have allergies, you may have some of the following symptoms:

  • swelling of the lips, tongue, face and eyes
  • difficulty breathing
  • a rash with hives or welts
  • abdominal (tummy) pain and vomiting

If you have an autoimmune condition, the symptoms will vary depending on what part or your body is affected.

Resources and support

Read more on your immune system at Australasian Society of Clinical Immunology and Allergy (ASCIA).

For tips on keeping your immune system health, read the article from Heart Research Australia.

The Baker Institute has tips on Food and your immune system.

Learn more here about the development and quality assurance of healthdirect content.

Last reviewed: July 2023


Back To Top

Need more information?

These trusted information partners have more on this topic.

Top results

Food and your immune system

Maintaining a healthy, balanced diet is key to helping your immune system function properly.

Read more on Baker Heart and Diabetes Institute website

Causes of IBD | Immune System - IBDclinic.mindovergut.com

Causes of IBD: Exact cause of IBD remains unknown, genetics appear to play some part in risk of developing IBD. Immune system is your body’s defence system

Read more on Mindovergut.com website

Immune system - Australasian Society of Clinical Immunology and Allergy (ASCIA)

Immune system

Read more on ASCIA – Australasian Society of Clinical Immunology and Allergy website

Immune system explained - Better Health Channel

The immune system remembers every germ it has ever overcome.

Read more on Better Health Channel website

How your baby's immune system develops

Learn how your baby's immune system develops and how breastfeeding and vaccinations help protect babies from serious illness.

Read more on Pregnancy, Birth & Baby website

Hughes syndrome - Better Health Channel

Hughes syndrome is thickening of the blood caused by abnormal immune system cells.

Read more on Better Health Channel website

How do vaccines affect immunity? | Sharing Knowledge about Immunisation | SKAI

Vaccines can’t overwhelm a baby’s immune system because their immune system is equipped to protect them from thousands of germs every day

Read more on National Centre for Immunisation Research and Surveillance (NCIRS) website

Vaccination and antibodies - MyDr.com.au

See how vaccines prepare your immune system to fight disease by taking advantage of the fact that the immune system can remember infectious organisms.

Read more on myDr website

Allergies | Pathology Tests Explained

Allergies (also known as ‘hypersensitivities’) are overreactions of the immune system to substances that do not cause reactions in most people. Hypersensitiv

Read more on Pathology Tests Explained website

Rheumatoid arthritis — Arthritis Australia inflammatory form of arthritis

Rheumatoid arthritis is an autoimmune disease that causes pain and swelling of the joints. The normal role of your body’s immune system is to fight off infections to keep you healthy. In an autoimmune disease, your immune system starts attacking your own healthy tissues. In RA, the immune system targets the lining of the joints, causing inflammation and joint damage

Read more on Arthritis Australia website

Healthdirect 24hr 7 days a week hotline

24 hour health advice you can count on

1800 022 222

Government Accredited with over 140 information partners

We are a government-funded service, providing quality, approved health information and advice

Australian Government, health department logo ACT Government logo New South Wales government, health department logo Northen Territory Government logo Queensland Government logo Government of South Australia, health department logo Tasmanian government logo Victorian government logo Government of Western Australia, health department logo

Healthdirect Australia acknowledges the Traditional Owners of Country throughout Australia and their continuing connection to land, sea and community. We pay our respects to the Traditional Owners and to Elders both past and present.