McColl J. Willowherb (Epilobium angustifolium L.): Biology, chemistry, bioactivity and uses. Agro-Food-Industry Hi-Tech. May/June 2002:18-22.
Epilobium angustifolium L. is a circumpolar member of the evening-primrose family (Onagraceae). The plant is an abundant perennial that dominates many plant communities undergoing succession, quickly reclaiming disturbed ground such as cut or burned forest, thus explaining its common name, fireweed. It is also commonly known as rosebay willowherb and great willowherb. Willowherb is often employed as the English name for the worldwide species. Canadian Willowherb has been used to describe the plant growing in Canada, which appears to possess distinct characteristics from the European plant.
Although sometimes considered a weed, it has a long history of use as both a food and a medicinal. Historically, medicinal use includes oral use of the plant extracts, often in the form of an infusion or tea, as a treatment for prostate and urinary problems including benign prostatic hyperplasia (BPH) or enlarged prostate; and for various gastrointestinal disorders such as dysentery or diarrhea. Topically the plant has been used traditionally as a soothing, cleansing and healing agent to treat minor burns, skin rashes, ulcers, and numerous other skin irritations and afflictions. Chemically, the plant contains an abundance of phenolic compounds, tannins and flavonoids, many of which appear to have biological activity. Willowherb extracts possess antimicrobial effects against a number of bacteria, including recently discovered activity of the Canadian Willowherb extract, along with isolated constituents, against the bacteria, Propionibacterium acnes. Myricetin 3-0-glucuronide has been identified as one of the anti-inflammatory components of willowherb. A special elagitannin, oenothein B, is present in the plant and appears to be an active anti-inflammatory component. The reported anti-cancer activity of willowherb extract may be related to the content of oenothein B, which has been found to exhibit potent anti-tumor properties, as well as cause inhibition of the 5-alpha-reductase enzyme. This explains the antihyperandrogenic effects that may be useful in the prevention and treatment of BPH, as well it supports the use of the extract in the prevention and treatment of prostate cancer. Scientific research has revealed the potential of oenothein B or similar compounds as useful antiviral and anticancer chemotherapeutic agents. The anti-cancer and analgesic properties of willowherb extract have been the subject of recent investigations, where significant activity has been found. The most tangible commercial applications of Epilobium angustifolium to date appear to be those related to the topical use of the extracts for their potent anti-irritant, anti-inflammatory, and free radical-scavenging effects. Commercial extracts of the plant are widely used in cosmeceuticals and personal care products ranging from creams, lotions, and shampoos to hair tonics and baby wipes. Therapeutic products for various skin conditions such as those for eczema, psoriasis, seborrhea, fungal infections, and rosacea have incorporated willowherb as a functional active ingredient. The main nutraceutical, cosmetic and therapeutic uses of willowherb and its extracts have, over the past 20 years, received scientific support and are explainable, at least in part, by the unusual chemical make-up of the plant.