It can also reduce the length of a cold by an average of 1.4 days, according to research by the University of Connecticut School of Pharmacy.
The study found that the herbal extract cut the chances of developing a naturally caught cold by 65 per cent and, for those who were directly given the cold-causing virus, by 35 per cent.
Echinacea, thought to boost the immune system, is found in more than 800 products.
Writing in the Lancet Infectious Diseases journal, the researchers said: "An analysis of the current evidence in the literature suggests that Echinacea has a benefit in decreasing the incidence and duration of the common cold.
"However, large-scale randomised prospective studies controlling for variables such as species, quality of preparation and dose of Echinacea, methods of cold induction and objectivity of study endpoints evaluated are needed before Echinacea for the prevention or treatment of the common cold can become standard practice."