What is the difference between the flu and a cold?

Flu and the common cold are both respiratory illnesses, but they are caused by different viruses. Because they have similar symptoms, it may be difficult to tell the difference between them based on symptoms alone. 

Flu symptoms tend to occur suddenly, while cold symptoms occur gradually. People with the flu are more likely to have a fever or chills, muscle or body aches, headaches, and fatigue (tiredness). People with colds are more likely to have a runny or stuffy nose, sore throat, and sneezing. Cold symptoms are usually milder and generally do not cause serious health problems.