Although colds and influenza are both respiratory infections, they are caused by different viruses. And while symptoms may seem similar, it is important to be diagnosed correctly to avoid complications from flu, like pneumonia.

According to the U.S. Centers for Disease Control and Prevention, flu symptoms -- including body aches, fever, cough and fatigue -- are typically much more severe than a cold's. Congestion and a runny nose are more typical symptoms of a cold than the flu.

A cold will usually clear up on its own. The flu, however, can lead to serious complications -- especially in the elderly or people with chronic diseases such as diabetes. Left untreated, the CDC says, flu can lead to pneumonia and bacterial infection.