Strep throat is a bacterial throat infection that can make your throat feel sore and scratchy. Only a small portion of sore throats are the result of strep throat. It's important to identify strep throat for a number of reasons. If untreated, strep throat can sometimes cause complications such as kidney inflammation and rheumatic fever. Rheumatic fever can lead to painful and inflamed joints, a rash and even damage to heart valves.