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Echinacea is an herb that has been used to prevent and treat symptoms related to respiratory illnesses such as common colds and the flu. For many years, people have believed that this herb stimulates the immune system to fight infections. To date, studies have revealed mixed results as to whether echinacea prevents or shortens illness.

The species of plants known as Echinacea are flowering perennials that are native to the East and Midwest regions of the United States. There are nine species, and three are used in supplements: Echinacea purpurea, Echinacea angustifolia and Echinacea pallida. The whole plant and its roots are used to make supplements, depending on the brand. A liquid extract made from the root of Echinacea purpurea is the most popular form of echinacea supplement. The roots and above-ground plant parts have different chemical properties that can influence the effectiveness of the herb.

Echinacea is sold under various trade names. It is one of the most popular supplements in the United States. The National Institutes of Health (NIH) estimates that echinacea supplements account for about 10 percent of all supplement sales in the United States. In addition to being used to prevent or treat infections such as a cold or the flu, people have used echinacea to treat wounds and skin problems, including acne and boils (tender, swollen areas that form around hair follicles).

Scientific studies into the health effects of echinacea have revealed mixed results. The NIH  conducted two studies that revealed no link between taking echinacea regularly (e.g., on a daily basis) and the prevention of colds and other infections. As a result, the NIH concluded that echinacea does not appear to be useful in preventing these illnesses.

However, other studies have indicated that echinacea may provide benefits to those with upper respiratory infections. The NIH and other organizations are continuing to conduct clinical trials to explore the potential link between echinacea use and a reduction in the severity and duration of illnesses such as colds and the flu.

One of the problems with herbal supplements is the issue of standardization. Supplements are not regulated by the U.S. Food and Drug Administration (FDA) and manufactureres are not obligated to comply with the safety standards required of medications. In addition, it is difficult to know what part of the plant is contained in the supplement, which could influence the effectiveness of the herb. It is also difficult to reliably determine what species of echinacea and how much echinacea are contained in supplements. Furthermore, even plants of the same species may have different variations of active compounds depending on factors such as individual genetic differences, how the plant was grown and how it was harvested.

The potential effect of echinacea on other medical conditions is also being studied. These conditions include:

• Genital herpes
• Radiation-associated toxicity
• Skin and oral wounds
• Vaginal yeast infections (candidiasis)