There are over 8,000 known naturally occurring plant phenolics, and a large proportion of these are flavonoids. Structurally, polyphenols have at least one aromatic benzene ring with several hydroxyl (–OH) groups attached. In many families, such as the flavonoids, there are two or more rings with varying degrees of hydroxylation. These hydroxyl groups are what give polyphenols many of their characteristic properties.

In herbal medicine, polyphenols are often responsible for colour (yellows, reds, blues), as well as much of the bitterness and astringency we taste in plant preparations. Their actions are frequently linked with antioxidant, anti-inflammatory, and vascular-supporting effects, and they can also show hepatoprotective activity, as seen with the flavonolignan silybin from Silybum marianum (milk thistle).

On this page, you’ll find a few key polyphenols in 3D, so you can explore their shapes while you learn what they do.