Signs and Symptoms of the Flu (Influenza)

Flu Symptoms Image

The flu is an acute illness, meaning that symptoms usually come on suddenly. Infection usually lasts about one week and most patients recover without medical treatment within two weeks.

Flu viruses affect the respiratory tract and cause headache, runny or stuffy nose (rhinitis); dry, persistent cough; and sore throat. In some cases, cough associated with the flu can last longer than 2 weeks. Influenza also causes systemic symptoms, including the following:

  • Chills
  • Extreme tiredness (fatigue)
  • Fever (usually high)
  • Malaise (generally feeling unwell)
  • Muscle aches (especially in the legs and back)

Nausea, vomiting, diarrhea, and ear infection (otitis media) also may occur with the flu. These symptoms are more common in children. Viruses that affect the gastrointestinal tract (e.g., stomach, intestines) often cause nausea, vomiting, and diarrhea. These illnesses may be referred to as "stomach flu," but they are not caused by influenza viruses.

Common Cold vs. Flu

The common cold is a respiratory illness also caused by a virus. It can be difficult to tell the difference between a cold and the flu on the basis of symptoms. In most cases, symptoms of the flu (e.g., fever, muscle aches, tiredness, cough) are more severe and come on more suddenly. Colds usually do not lead to complications such as pneumonia or bacterial infections.

Publication Review By: Stanley J. Swierzewski, III, M.D.

Published: 01 Aug 2007

Last Modified: 22 Sep 2015