Overview of Colds & Flu

The common cold and influenza (flu) are among the most common viral infections.

Common Cold

The common cold is caused by a virus. Colds can occur at any time, but occur more frequently in the spring and fall. The virus infects the upper respiratory tract causing a runny nose, sneezing, and sore throat.

Colds are generally mild and self-limited. If the immune system is healthy, a cold normally does not last more than 2-3 days. The common cold can be distinguished from the flu by the type and severity of symptoms. Flu symptoms include stuffy nose, sore throat, cough, fever, headache, body aches, malaise, and muscle weakness. The flu usually is more severe than a cold and often occurs in epidemics.

The viruses that cause colds are always in the environment, but most people only catch 1 or 2 colds a year. A healthy immune system identifies and eliminates the cold virus before it can cause an infection. If the immune system is weak or compromised, a virus can take advantage of the condition cause infection. Catching more than 1 or 2 colds a year or developing chronic or serious complications from the infection is an indication of a weak immune system.


Influenza, or the flu, also is caused by a virus. The flu is more common in the winter and often occurs in epidemics. The flu virus infects the upper and lower respiratory tract causing headache, fever and chills, aching muscles and joints, fatigue, weakness, sore throat, and cough.

The onset is usually extremely abrupt and symptoms generally last about 2–5 days, but weakness and fatigue may persist for weeks. Influenza can be fatal, particularly in the very young and very old, or if a secondary infection, such as pneumonia, develops. Having a healthy immune system can help prevent infection and reduce the duration of the flu.

Immune System

The immune system can be weakened by the following:

  • Alcohol, drug, and tobacco consumption
  • Allergies
  • Chemical exposure
  • Excessive sugar consumption
  • Physical, emotional, and mental stress
  • Poor nutrition
  • Nutrient deficiency

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

Published: 01 Jan 2001

Last Modified: 08 Sep 2015