Symptoms usually come on suddenly, according to the CDC, and can include fevers above 100.4 degrees F, dry cough, sore throat, runny nose, body aches, headaches, chills and occasionally nausea, vomiting or diarrhea.

— The flu, caused by influenza viruses that are always changing, leads to fever, chills, cough, sore throat, runny nose, body aches, headaches and feeling tired. Flu symptoms tend to hit more quickly than cold symptoms, and can last anywhere from a few days to two weeks.