The herbal remedy echinacea could halve a person's risk of catching a cold, say US researchers.
Echinacea is native to North American prairies and is thought to boost the body's immune system.
Researchers from the University of Connecticut School of Pharmacy say it can also decrease the odds of developing a common cold by 58% and its duration by a day-and-a-half.
Published inside The Lancet Infectious Diseases, the scientists reviewed 14 different studies on Echinacea's effects on the immune system.
People were 86% less likely to catch a cold when taking Echinacea combined with a vitamin C supplement. Echinacea alone reduced their chances of falling ill by 65%.
When given to people directly inoculated with a rhinovirus, echinacea reduced their chances of catching a cold by 35%.
The scientists say more research is needed to check that the safety of the different echinacea formulas, before making any recommendations.