Scientific studies have shown that zinc kills any rhinovirus - not just one or two like a vaccine. Zinc also decreases nasal irritation and drainage. This makes those tissues a poor place for viruses to multiply, and gives immediate relief of symptoms.

It is important to start treatment early. On average, untreated colds last a little over nine days. Studies show that zinc lozenges reduce the average to about 5 days, but only if you start treatment no later than the morning of the third day. After the third day, you will still get symptomatic relief, but the cold will probably last 7 to 10 days.

Cleveland Clinic researchers studied 100 patients who had cold symptoms for less than 24 hours; half took a zinc lozenge product called and the other half took a placebo. The ones who took the zinc lozenges reduced the length of their cold by 42 percent.

"It was a surprisingly dramatic effect. There was nearly a 50 percent reduction in the duration of the symptoms of the common cold; it went from 7.6 to 4.4 days," said Dr. Michael Macknin of the Cleveland Clinic. "It's the first thing I'm aware of that actually has decreased the duration of cold symptoms to this extent."

Other cold remedies only relieve the symptoms, without changing the course of the cold.