While symptoms of cold and flu are similar in some respects (e.g. runny nose, sneezing, etc.), the flu develops more quickly, and can cause more discomfort.  Colds are infections of the upper respiratory system:  the nose and the throat.  The flu, in contrast, affects the entire body and lungs and is more serious due to the nature of the symptoms.  For example, bronchitis and pneumonia can develop from the flu.

Symptoms of a flu virus may start out as a sniffle or cough, and involve a runny nose.  However, the flu quickly develops more severe symptoms.  These symptoms affect the entire body, not just your head and throat.  Your body may hurt too much, and feel too weak to get out of bed.  Also, flu symptoms will develop very quickly, and will last longer.  You can be sick from the flu from 1 to even 3 weeks.  Flu symptoms are severe enough to result in days spent at home from school and work, and generally make life miserable. Symptoms of the flu include:

• Chills and sweats
• Diarrhea and vomiting in children
• Dry cough
• Fatigue and weakness
• Fever over 101 F (38 C) in adults, and often as high as 103 to 105 F (39.5 C to 40.5 C) in children
• Headache
• Loss of appetite
• Muscular aches and pains, especially in your back, arms and legs
• Nasal congestion

The severity of flu symptoms are likely to be worse with those who are prone to complications, and may require hospitalization.  Symptoms may progress rapidly within just 24 hours.  In other words, you may feel ok in the morning, but significantly sicker by the afternoon or evening. 

When to seek medical help
Even in healthy persons, the flu can potentially be life-threatening.  Whereas a cold is manageable, the flu should be taken seriously with help from a doctor.  Seeing your family physician is usually the first step taken to beginning treatment.  You should seek a doctor's advice immediate immediately if you fall ill with the flu and are elderly, have a weakened immune system, or are a young child.  Also, treatment should be sought immediately for those with complications.

Diagnosing the flu early can help you take actions to get better sooner.  To understand how your doctor will make a diagnosis so that you can begin treatment, read about how to diagnose either the cold or flu virus in our Diagnosing Flu section that follows.