At worst, a cold can occasionally lead to secondary bacterial infections of the middle ear or sinuses, which can be treated with antibiotics. But if the flu is misdiagnosed as a bad cold, potentially life-threatening flu complications like pneumonia may be overlooked. Some of the symptoms of a cold and flu are similar, but the two diseases can usually be distinguished. Typically, colds begin slowly, two to three days after infection with the virus. The first symptoms are usually a scratchy, sore throat, followed by sneezing and a runny nose.
Temperature is usually normal or only slightly elevated.
A mild cough can develop several days later. Cold symptoms usually last from two days to a week. Signs of the flu include sudden onset with a headache, dry cough, and chills. The symptoms quickly become more severe than those of a cold. The fever typically begins to subside on the second or third day, and then respiratory symptoms like nasal congestion and sore throat appear.