Bacteria and viruses can both make us sick, but what makes them different? And why does that matter when treating an infection?

Although both can cause infections, bacteria and viruses are very different types of microorganisms.

Bacteria are single-celled organisms that can feed themselves and reproduce independently. They are found almost everywhere—in the air, water, soil, and even on and inside our bodies. Some bacteria are harmless or beneficial, while others can cause disease. Bacteria can multiply very quickly: under favorable conditions, one bacterial cell can potentially become millions of cells within just a few hours.

Viruses are much smaller than bacteria and behave differently. They cannot grow or reproduce independently. Instead, they must enter a living host cell and use the cell’s machinery to make new copies of themselves. Once a virus enters the body, it attaches to and enters susceptible cells, then uses the cell’s internal machinery to produce more viral particles.

Why does this difference matter?
Because bacteria and viruses work differently, their treatments are different too. Antibiotics can treat certain bacterial infections, but they do not work against viruses. Viral infections may instead be managed with supportive care or, for some viruses, specific antiviral medications.

In simple terms: bacteria can reproduce on their own, while viruses need a living cell to reproduce.