Antibiotics are strong medicines used to treat infections, including life-threatening contagious diseases. But antibiotics can cause more harm than good when they aren't used the right way. You can protect yourself and your family by knowing when you should use antibiotics and when you should not. Ear infections. 2  There are several types of ear infections. 3  Antibiotics are used for some (but not all) ear infections. 4  Sinus infections. 5  Antibiotics are often used to treat sinus infections. 6  However, a runny nose and yellow or green mucus do not necessarily mean you need an antibiotic.