Some of the symptoms do overlap—the sore throat, the stuffy nose—but a cold tends to be concentrated in the upper respiratory system, with sneezing and watery eyes. The flu is less likely to come along with a runny nose, but instead will cause muscle aches and chills. Depending on the particular strain of the flu circulating, it can also cause an upset stomach or diarrhea. The real hallmark of the flu, though, is a high fever, Benson says. A cold might cause a low grade, borderline fever, she says, but with the flu, body temperature spikes.