Science
How does the immune system work?
Quick answer
The immune system is your body's defence team. It stops germs getting in, finds the ones that do, and destroys them, using white blood cells, antibodies and protective barriers.
In one sentence
The immune system is the network of cells, tissues and barriers that protects your body from germs and helps you recover from illness.
Explained
Germs are everywhere. Tiny living things called bacteria and even smaller viruses (plus some fungi) can cause disease. Together they are called pathogens. Your body has a layered defence to keep them out and to deal with those that get in.
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First line: barriers. Your skin is a tough wall. Your nose and throat make sticky mucus and have tiny hairs that trap dust and germs. Tears and saliva contain chemicals that kill bacteria, and strong acid in your stomach destroys many germs that you swallow.
Second line: white blood cells. If germs get past the barriers, white blood cells in your blood spring into action. Some surround and swallow germs. Others make antibodies, special proteins that stick to a particular germ like a key fitting a lock, and mark it for destruction. Swelling, redness and fever are signs that your body is fighting back. A raised temperature makes it harder for some germs to multiply.
Memory. After you have fought off a germ, your body remembers it. If the same germ returns, your immune system recognises it quickly and stops it before you feel ill. That is why you usually catch diseases like chickenpox only once.
Vaccines use this memory. They contain a harmless piece or a weakened form of a germ, so your body can practise making antibodies without getting sick. Then it is ready if the real germ appears. Vaccines have saved many millions of lives.
Medicines called antibiotics can kill bacteria, but they do not work against viruses. Sometimes the immune system overreacts to something harmless, like pollen or peanuts, which is an allergy.
You can help your immune system by washing your hands, sleeping well, eating a varied diet (see healthy eating), being active and getting your vaccinations. All of this happens in the cells of the human body.
Examples
| Defence | How it helps |
|---|---|
| Skin | blocks germs |
| Mucus | traps germs in nose and throat |
| Stomach acid | kills swallowed germs |
| White blood cells | find and destroy germs |
| Antibodies | mark specific germs |
| Vaccines | prepare the body in advance |
Common mistakes
- "Antibiotics cure colds." Colds are caused by viruses.
- "A fever is always bad." It is part of how the body fights germs, though a very high fever needs a doctor.
- "A vaccine gives you the disease." It teaches your body without making you ill.
Quick quiz
The immune system
Check what you know with 4 quick questions.
Question 1 of 4
Which cells are the main fighters of the immune system?
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