An antibiotic is a medicine that kills bacteria or stops them from multiplying inside your body. When you get an infection like strep throat or an infected cut, bacteria are invading your body and making you sick. Antibiotics are designed to attack those bacteria without harming your own cells.

Before antibiotics were discovered in 1928, people died from infections that seem minor today. A small cut could lead to a deadly infection. Pneumonia, tuberculosis, and other bacterial diseases killed millions. The discovery of penicillin, the first widely used antibiotic, changed medicine forever and saved countless lives.

Antibiotics only work against bacteria, not viruses. That's why your doctor won't prescribe antibiotics for a cold or the flu: those illnesses are caused by viruses, which antibiotics can't touch. Taking antibiotics when you don't need them can actually create problems, because bacteria can evolve to resist the medicine, making it less effective when you really need it.

When prescribed properly and taken exactly as directed, antibiotics are one of medicine's most powerful tools.