The common cold and the flu are both respiratory illnesses with similar symptoms, but they are caused by different viruses. While the flu is caused only by the influenza virus, colds are caused by rhinovirus and a number of other viruses. The three things that distinguish cold and flu symptoms are severity, speed of onset, and type of symptoms.
A cold typically comes with a stuffy nose, sore throat, and/or sneezing and symptoms develop gradually. Flu symptoms are typically more severe than cold symptoms and tend to come on more quickly. Symptoms more common with the flu include fever, fatigue, and/or aches. Cold and flu symptoms are very similar, though, so it’s best to confirm which respiratory virus you have with a flu test when symptoms arise. Talk to your healthcare provider if you think you need to take a flu test.