Few illnesses are as stubbornly resistant to treatment as the common cold. In a world of often startling medical advancements, scientists have yet to crack the code on this pervasive illness. According to some estimates, an average of 1 billion cases of the common cold occur annually in the United States.

Influenza is another of the most common infectious diseases caused by a virus. It infects between 5 and 20 percent of the population in United States every year, according to the U.S. Centers for Disease Control and Prevention.

In recent years, millions of Americans have turned to over-the-counter alternative cold and flu treatments to try to nip these illnesses in the bud. At the first hint of a sniffle, some people begin chewing vitamin C supplements like candy. Others begin a steady diet of zinc lozenges, the herbal remedy echinacea, or other substances such as eucalyptus, garlic, honey, lemon and menthol.

Treatments also are available that combine several of these substances with other ingredients (such as antioxidants and electrolytes) in a type of “anti-virus cocktail†designed to fight both colds and influenza. These products are often marketed to travelers as a way to ward of germs circulating through airplanes.

The million-dollar question, of course, is whether or not these treatments actually work. Years of scientific studies point to the same answer: probably not much, if at all.