Bacteria are single cells that can survive on their own, inside or outside the body. Viruses cause infections by entering and multiplying inside the host's healthy cells. They can't reproduce on their own (unlike bacteria), and they need to enter a living cell (such as a human cell) to be able to reproduce. Therefore, they are not considered "living", but they can survive by forcing host cells to make new viruses. It can be difficult to know what causes an infection because viral and bacterial infections can cause similar symptoms. Antibiotics won't cure viral infections. Antibiotics won't work for viral infections. Misusing antibiotics to treat viral infections contributes to the problem of antibiotic resistance.