A review of the medical research on zinc shows that when it is taken within one day of the first symptoms, it can cut down the time you have a cold by about 24 hours. It also greatly reduces the severity of symptoms.
The authors of the review did not make any suggestions as to what type of zinc product to buy. They also did not suggest an optimal dose or formulation, stating that more research was needed before such a recommendation could be made.
Zinc supplements also have downsides -- they can cause nausea and a bad taste in the mouth, and they may interfere with your body's uptake of other key minerals.
According to the New York Times:
"Zinc experts say that many over-the-counter zinc products may not be as effective as those studied by researchers because commercial lozenges and syrups often are made with different formulations of zinc and various flavors and binders that can alter the effectiveness of the treatment."
Colds are transmitted only by droplets, such as from sneezing, that come from a person who's infected. These droplets can, however, remain on surfaces for some time. Colds normally last about seven days.
Cold medicines are not recommended for children under 4, and no cold medicines are cures -- they only relieve symptoms. Washing your hands is still the number one recommended way to keep yourself free of colds.