What Causes a Cold or the Flu?

Distinguishing Between Colds and Flu  

What Exactly Is a Cold?

Every one of the 1 billion annual cases of the common cold in the United States begins when a tiny dose of a virus is inhaled into the nasal passages from droplets sneezed or coughed into the air or transmitted by contaminated fingers. The virus then moves to the back of the nose, where it attaches itself to the adenoid area and begins to reproduce. Within 10 to 12 hours, the body attempts to defend itself by releasing mucous-gland secretions and by sneezing and coughing―the cold symptoms you begin to feel. Typically, symptoms worsen over the first 48 hours, then start to diminish. Most colds last about one week, though a severe case may linger a bit longer.

What Exactly Is the Flu?

If a cold is like being sideswiped by a bike messenger, the flu is like being run over by a truck. Caused by the influenza virus, it comes on more suddenly than a cold, and the symptoms, which usually last four to five days, are generally worse. Your fever can be moderate to high―usually 101 to 103 degrees. Body aches and fatigue may be more intense, and your cough will be dry and hacking rather than wet. You’re more likely to have a headache and chills and less likely to get a sore throat or a runny nose. Because the flu invades the bronchial tubes and the lungs, it’s more serious than a cold.

How You Catch Them

It’s more accurate to say that the flu or a cold virus catches you. Both are spread in the same two ways. An infected person coughs or sneezes, shooting virus particles into the air, which you breathe in. Or you touch an object―a doorknob, someone’s telephone―contaminated with the virus and then carry it to your nose or tear ducts with your fingers.