Cause: Various viruses.

Useful Supplements: Vitamin C, Zinc.

Useful Herbs: Echinacea.

Further information: Colds are the most common ailment to effect humans. More than 200 viruses that cause colds have been identified; there are undoubtedly even more. These viruses spread easily both via air and through physical contact.
The common symptoms of a cold include sore throat, achiness, sneezing, congestion, runny nose, cough, and low fever. More severe symptoms are probably caused by influenza.
There is no guaranteed way to prevent catching colds. Washing hands often may help decrease the number of germs that are living there. Several herbs and supplements have been shown to help boost immunity, and may help in the prevention of colds.
There is no cure for the common cold, only symptomatic treatment. Rest, proper nutrition, and drinking lots of water may help ease the symptoms. With or without treatment, however, most colds last about seven to ten days.

The following herbs and supplements have been shown to help in treatment of colds, and in boosting immunity:

Vitamin C is a strong antioxidant, and has been shown in clinical studies to boost immunity.¹ This may help to prevent colds.

Zinc has been shown to help decrease the severity and length of duration of colds.² The reason this happens is not clear, but researchers suspect that the Zinc inhibits the ability of the virus to bind to body cells.

Echinacea has been shown to inhibit the development of colds into severe upper respiratory infections, and to speed recovery times.³

For further information on supplements and herbs that may help boost immunity and prevent the onset of colds, see Immune Boosters.

References:

¹Johnson, C, American Journal of Clinical Nutrition (58:103-5; July 1993).
²Mossad, S.B., et al. "Zinc gluconate lozenges for treating the common cold. A randomized, double-blind, placebo-controlled study," Ann Intern Med 15;125(2): 81-88, July 1996.
³Hoheisel O, et al. Echinagard treatment shortens the course of the common cold: a double-blind, placebo-controlled clinical trial. Eur J Clin Res 1997;9:261_8.