What causes colds and the flu?

Colds and the flu are primarily caused by viruses, which are infectious agents that replicate inside the living cells of an organism. The most common viruses responsible for these illnesses are rhinoviruses and influenza viruses. Unlike bacteria, which are single-celled organisms that can thrive in various environments, viruses require a host cell to reproduce and spread. This viral infection leads to symptoms such as coughing, sneezing, fever, and body aches, which are typical responses of the immune system to fight off the invading viruses.

While other factors like parasites and bacteria can cause illness, they are not the root causes of colds and flu. Environmental factors, such as temperature changes and stress, can impact overall health and susceptibility to these viral infections but do not directly cause them. Understanding that viruses are the primary culprits helps in preventing the spread of these illnesses, emphasizing the importance of hygiene practices such as handwashing and vaccination against the flu virus.