Health elementary May 24, 2026

Why Do You Catch a Cold When Someone Else Has One?

How tiny viruses move from person to person

A child with a cold covering a sneeze while another child washes hands, showing how germs can spread and how hygiene helps stop them.

You catch a cold when cold viruses get into your nose, mouth, or eyes. They can travel in tiny wet drops from a cough or sneeze, or they can sit on hands and surfaces. Washing hands, covering coughs, and keeping space from sick people help block the virus.

Big Idea. NGSS 1-LS1-1 and 3-LS3-2 help students connect body systems and variation to how people notice, respond to, and fight germs.

A cold often seems to move through a classroom, a family, or a bus. One person starts sneezing. A few days later, someone nearby has a runny nose too. That pattern happens because colds are caused by viruses. A virus is a tiny germ that can make copies of itself inside living cells. Cold viruses usually enter through the nose, mouth, or eyes. They can ride in small wet drops when someone coughs, sneezes, talks, or wipes a nose. They can also land on a desk, toy, pencil, or doorknob. Then a hand can pick them up and carry them to the face. Your body is not helpless. Your immune system notices the invader and fights back. The stuffy nose, mucus, cough, and tired feeling are signs that your body is working. A cold is common, but it is also a real example of how living things interact.

A cold starts with a virus

A simplified cold virus near cells in the lining of a child's nose, showing where infection can begin. — Cold viruses enter through the nose, mouth, or eyes

A cold is not caused by cold air. It is caused by a virus. Many different viruses can cause cold symptoms. Rhinoviruses are one common group. A virus is much smaller than a dust speck. It cannot grow like a plant or animal. Instead, it must get inside a living cell and use that cell to make more copies. Cold viruses often enter cells that line the nose and throat. Those cells are part of your respiratory system, which helps you breathe. Once the virus makes more copies, nearby cells can become infected too. That is why symptoms may start small, then become stronger after a day or two. The virus does not care whether you are wearing a coat. It spreads best when it reaches the right body parts. That is why keeping germs away from your face matters.

Cold air does not cause a cold, but a cold virus can.

Droplets carry germs

A child coughing into an elbow with small droplets shown moving a short distance and falling onto a nearby desk. — Droplets can move viruses from one person to nearby places

When a sick person coughs, sneezes, talks, or laughs, tiny wet drops can leave the mouth or nose. These drops are called respiratory droplets. They may carry cold viruses. Some drops fall quickly onto nearby surfaces. Some can be breathed in if another person is very close. This is why a sick person should cover coughs and sneezes with a tissue or an elbow. It is also why staying home when sick can protect classmates and family members. Droplets are usually too small to see, so people may spread a virus without noticing. A person can also spread a cold before feeling very sick. That makes simple habits important every day, not only when someone looks ill. Covering a cough does not make all germs disappear. It lowers how many droplets fly into the air and land on nearby people or things.

Covering coughs and sneezes helps trap virus-carrying droplets.

Hands and surfaces help spread colds

A sequence showing a hand touching a doorknob, then another hand touching the same doorknob, then a hand near an eye. — Surfaces can pass viruses to hands

Cold viruses can also spread by touch. A sick person may wipe a nose, then touch a pencil, tablet, toy, or doorknob. The virus can stay on that surface for a while. Another person may touch the same surface, then rub an eye or pick up a snack. The virus now has a path into the body. This is called indirect contact because the virus moves through an object instead of directly from one person to another. Shared classroom materials can make this easy. Cleaning surfaces can remove some germs, but hands are often the main carriers. People touch their faces many times each day without thinking about it. That is why teachers and doctors remind students to wash hands before eating, after using the bathroom, and after blowing the nose. Clean hands break the chain.

A virus on a surface is only a problem if it reaches your nose, mouth, or eyes.

Soap breaks the chain

Hands being washed with soap and running water, with virus particles shown lifting off the skin and going down the drain. — Soap, rubbing, and rinsing remove germs

Hand washing works because soap and water remove germs from skin. Soap helps loosen dirt, oil, and tiny particles that can hold viruses. Rubbing hands together lifts those particles away. Running water rinses them down the drain. The time matters because quick splashes miss many spots. Fingers, thumbs, nails, and the backs of hands all need rubbing. Many health groups suggest washing for about 20 seconds. Hand sanitizer can help when soap and water are not available, but it may not work as well on very dirty or greasy hands. Washing is simple, but it changes the path of a virus. If the virus leaves your hands before you touch your face or food, it cannot enter your body that way. Good hand washing is not perfect, but it lowers the chance of infection.

Soap does not need to be fancy. Rubbing and rinsing do the work.

Your immune system fights back

Immune cells surrounding cold virus particles while a child rests with water and tissues nearby. — The immune system clears most colds over time

After a cold virus enters the body, the immune system begins to respond. The immune system is a group of cells, tissues, and organs that help protect you. Some immune cells notice infected cells. Others help make tools that stick to germs and mark them for removal. Mucus can trap particles. A cough can push mucus and germs out of the airway. A mild fever can make the body less comfortable for some germs. These defenses can make you feel tired, stuffy, or achy. Most colds get better on their own because the immune system clears the virus. Antibiotics do not help a cold because antibiotics work against bacteria, not viruses. Doctors may suggest rest, fluids, and comfort care instead. The best plan is to help your body heal and avoid spreading the virus to others.

Antibiotics treat bacteria, so they do not cure a common cold.

Vocabulary

virus: A tiny germ that can make copies of itself inside living cells.
droplet: A small wet particle that can leave the mouth or nose during coughing, sneezing, talking, or breathing.
surface: The outside of an object, such as a desk, toy, pencil, or doorknob, where germs can land.
immune system: The body system that finds and fights germs.
antibiotic: A medicine used to treat some infections caused by bacteria, not colds caused by viruses.

In the Classroom

Glitter Germs

20 minutes | Grades K-5

Put a tiny amount of washable glitter on one student's hand and have the student shake hands or touch classroom objects. Students map where the glitter traveled, then test how soap and water remove it better than a quick rinse.

Droplet Distance Model

25 minutes | Grades 2-5

Use a spray bottle filled with water to model droplets from a cough or sneeze. Spray toward dark paper from different distances, then compare how many drops land on the paper.

Immune System Story Cards

30 minutes | Grades 3-5

Give students cards for virus, nose cell, mucus, cough, immune cell, rest, and water. Students arrange the cards into a simple story that explains how a cold starts and how the body fights back.

Key Takeaways

• Colds are caused by viruses, not by cold weather.
• Cold viruses can travel in droplets from coughs, sneezes, and talking.
• Hands can move viruses from surfaces to the nose, mouth, or eyes.
• Soap, rubbing, and rinsing remove many germs from hands.
• Antibiotics do not cure colds because colds are caused by viruses.

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