The common cold is generally mild and goes away on its own with most symptoms improving in one week. Severe complications, if they occur, are usually in the very old, the very young, or those who are immunosuppressed (have a weakened immune system). Secondary bacterial infections may occur resulting in sinusitis, pharyngitis, or an ear infection. It is estimated that sinusitis occurs in 8% of cases. Ear infections occur in 30% of cases.