Echinacea is thought to support the immune system by activating white blood cells. Three major groups of constituents may work together to increase the production and activity of white blood cells (lymphocytes and macrophages), including alkylamides/polyacetylenes, caffeic acid derivatives, and polysaccharides. More studies are needed to determine if and how echinacea stimulates the immune system in humans.
Echinacea may also increase production of interferon, an important part of the body’s response to viral infections. Several double-blind studies have confirmed the benefit of echinacea for treating colds and flu. Recent studies have suggested that echinacea may not be effective for the prevention of colds and flu and should be reserved for use at the onset of these conditions. In terms of other types of infections, research in Germany using injectable forms or an oral preparation of the herb along with a medicated cream (econazole nitrate) reduced the recurrence of vaginal yeast infections as compared to women given the cream alone.