A cold is caused by a viral infection of the upper respiratory tract (mainly the nose and throat), most often by a group of viruses called rhinoviruses. More than 200 different respiratory viruses can trigger a common cold, including rhinoviruses, common human coronaviruses, adenoviruses, enteroviruses, and others.
How the virus spreads
- Cold viruses spread in droplets when an infected person coughs, sneezes, or talks near you, and you inhale those droplets.
- They also spread when you touch contaminated surfaces (like door handles or phones) and then touch your eyes, nose, or mouth, letting the virus enter your body.
Why some people catch colds more
- Risk is higher in crowded places (schools, childcare, planes) where close contact makes spread easier.
- Young age, smoking or secondhand smoke, a weakened immune system, poor sleep, and fall–winter seasons all make colds more likely.
What actually causes symptoms
- Once the virus infects the lining of the nose or throat, the immune system responds, causing inflammation and extra mucus, which leads to a runny or stuffy nose, sore throat, and cough.
- Symptoms are mostly due to the body’s immune response to the virus rather than the virus directly damaging the tissues.
