Zinc has been controversial as a cold remedy because research has produced conflicting results. Nonetheless, a systematic review concluded that taking zinc lozenges at the first sign of cold symptoms can shorten the illness and reduce its severity (American Family Physician, July 15, 2012).

The lozenges have the drawback of tasting terrible; some people even find them nauseating. Although intranasal zinc may also help shorten colds, we don’t recommend it. Many people have found that it zapped their sense of smell, sometimes permanently.

Vitamin C is probably the best-known nutrient for treating colds. A review of 29 studies concluded that ascorbic acid supplements do not prevent colds, but might be somewhat helpful in shortening the duration of symptoms (Cochrane Database of Systematic Reviews, Jan. 31, 2013).

Probiotics are the most recent addition to the anticold arsenal. They contain beneficial bacteria that appear to strengthen the immune system.

One review of 10 studies found that people taking probiotics were substantially less likely to come down with an upper respiratory tract infection (CMAJ, Feb. 18, 2014). Lactobacillus casei and Lactobacillus rhamnosus GG were the probiotics used in the most promising trials.

Public health experts encourage frequent hand-washing to avoid catching a cold. Researchers at the University of Arizona put samples of a test virus on a single doorknob or tabletop at the start of a research project.

They then sampled surfaces such as tap handles, computer equipment and light switches. Within the first few hours, nearly two-thirds of these other surfaces were contaminated with the virus, suggesting that the spread is very fast.

Washing hands thoroughly is best; using an alcohol-based hand sanitizer in addition may help stop viral transmission.

The usual “antibacterial” hand soaps containing triclosan don’t offer any benefits against cold viruses beyond ordinary soap, so we do not recommend them.

What’s the best way to dry hands after washing — paper towels or hot air dryers? Australian researchers concluded that “paper towels are superior to electric air dryers” (Mayo Clinic Proceedings, Aug. 2012). Towels remove water faster and eliminate more bacteria from hands.