Colds can be caused by at least 5 different types of viruses, of which there are over 100 strains. A virus is a particle made up of a core of DNA or RNA enclosed by a protein coating. When a virus infects a human cell, it uses the cell's machinery to replicate itself.
Viruses are different from bacteria.
Bacteria are complete cellular organisms that can reproduce themselves Antibiotics work against bacteria because the bacterial cells are different enough from human cells for the medicine to kill the bacteria without harming the human cells. Designing medicines that kill viruses without harming human cells is difficult. No medicine yet exists that can cure infection from cold viruses. Fortunately, your body's immune system mounts a specific response to whatever cold virus you have. It usually clears the infection within 7 to 14 days.