our throat feels like it’s on fire. You’re
sneezing. Your nose is dripping like a leaky hose. Your muscles ache, and you have a fever. Oh no! Your body is under attack. Germs have invaded your body. Don’t worry. Your immune system is ready
to fight back. It’s your body’s defense system. It protects you from millions of germs. Let’s see how this system works.
Germs are around you all the time. Many germs live on your skin. T ey lurk inside your belly button. T ey hide in your mouth or between your toes. All of them are so small you can see them only with a microscope. Germs can get inside your body in many
ways. T ey can creep in through cuts. You can inhale them through your nose. T ey can hitch a ride to your guts on the food you eat. Germs in a mosquito’s spit can get under your skin when the bug bites you. If you shake the hand of someone who’s sick, their germs might rub off on you. T ese germs can cause big trouble once
they find a way into your body. T ey can cause infections. T ey can make you sick.
This virus is on the attack.
T ere are two main types of germs. One is bacteria. Bacteria are tiny living things called microorganisms. T ey’re unicellular, or made up of one cell. In some ways, bacteria are like tiny fish in
a huge sea. T ey swim inside your body. T ey eat nutrients that your body makes. T ey also multiply very quickly. One bacterium can turn into millions in a few hours! Some bacteria are harmful. T ey can cause
ear infections and strep throat. Not all bacteria are bad, though. As many as 700 types of good bacteria swim in your intestines. T ey help you digest food. Some kill bad bacteria. T e second main kind of germs is viruses.
T ey’re smaller than bacteria. T ey aren’t made up of cells, and they can’t multiply on their own. T at doesn’t mean they’re not scary. T ey are. Viruses are like parasites. T ey move into
a healthy cell and take control. T ey force the cell to make copies of the virus. Eventually, the virus makes so many copies that the cell bursts. T e new viruses spread to more cells. Viruses are usually bad for you. T ey can
cause flus, colds, and chickenpox. It’s hard to avoid them, though. A virus in a sneeze can reach you even if you’re standing 1 m away.
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