Germs are so tiny that you need a microscope to see them. There are several kinds, including bacteria, viruses and fungi. Most of them do not hurt people, and some even help. Only some make people sick. Those few spread when someone coughs or sneezes. Let us look at how they work.

Bacteria are living things made of just one cell. Under a microscope they look like balls, rods or spirals. They live almost everywhere on Earth, even in and on your body. Do not worry, because some of them help you. The bacteria in your gut help your body digest food.

A virus is different. It is made of genetic material inside a coat of protein. It cannot make copies of itself alone. It has to get inside a living cell and use that cell to make copies. A cold is caused by a virus. Colds spread through tiny drops in the air and on things people touch.

Germs can get into your body through your eyes, nose and mouth. So try not to touch your face with unwashed hands. Once germs are inside, they take energy from your body and can damage healthy cells. That is how they make you sick, and it is why washing your hands matters.

Your body fights back with its immune system. White blood cells are part of it. They go after germs and fight them. You may get a fever, which is a body temperature of 100.4 degrees Fahrenheit or higher. A vaccine gives you a head start. It teaches your immune system to recognize a germ before the real germ arrives.

Antibiotics are medicines that kill bacteria or stop them from growing. They do not work on viruses, so they do not help a cold. Thick yellow or green mucus does not mean you need them. Most colds go away on their own in about one to two weeks. Take antibiotics exactly the way a doctor tells you to, and never share them.

Soap is your best tool. Washing your hands with soap and water helps keep germs from making you sick. Scrub for 20 seconds, which is about as long as humming Happy Birthday twice. Antibacterial soap is not better than plain soap. Any soap works. Wash before you eat and after you use the toilet.

Germs spread when someone coughs or sneezes. They also spread when you touch something that has germs on it. So when you sneeze or cough, cover your mouth and nose with a tissue. Then throw the tissue away. Remember, small habits like this keep tiny germs from traveling to the next person.

Words to know

• bacteria: tiny living germs
• virus: tiny germ
• immune: germ-fighting
• vaccine: germ-training shot
• antibiotics: bacteria-killing medicines

The short version

Germs are tiny living things and other particles, such as bacteria, viruses and fungi, that can make people sick. Most do not hurt people, and some help. Your immune system fights the harmful ones, and washing your hands with soap for 20 seconds helps stop them spreading.

Quick facts

• Germs include bacteria, viruses and fungi.
• A virus cannot make copies of itself alone. It must use a living cell.
• Antibiotics kill bacteria and do not work on viruses.
• Scrub with soap for 20 seconds. Antibacterial soap is no better than plain soap.
• A vaccine teaches your immune system to recognize a germ before the real germ arrives.