Phenolics
Antioxidant compounds built around one or more phenol rings — the flavonoids, tannins, phenolic acids, coumarins, and pigments behind much of a plant's protective chemistry.
Phenolics are organic compounds built around at least one phenol unit — an aromatic (benzene) ring carrying one or more hydroxyl groups. Where a molecule strings several such rings together it is termed a polyphenol, and it is this family — the flavonoids, tannins, phenolic acids, coumarins, lignans and pigments — that supplies much of a plant's protective chemistry. The reactive hydroxyl groups readily donate hydrogen and neutralise free radicals, which is the structural root of their reputation as antioxidants.
They are extraordinarily abundant. Phenolics form the largest single group of plant-derived antioxidants, and in one guise or another they colour flowers and fruit, screen leaves against ultraviolet light, deter grazing insects, and defend against microbial attack. Almost every plant tissue that has been examined carries them in some quantity, which is why they are so prominent across both the herbal materia medica and the ordinary diet.
Classification rests on that shared structural signature rather than on any single biological effect: a compound qualifies as a phenolic when it bears a hydroxyl group directly bonded to an aromatic ring. From that common motif the subgroups diverge widely in size and behaviour, from a simple phenolic acid of a few atoms to a condensed tannin large enough to precipitate proteins.
As a class the pattern is reassuring. Phenolics are overwhelmingly the benign, well-tolerated antioxidant and anti-inflammatory workhorses of plant medicine and food, and most are consumed daily without incident. The exceptions are mild and worth naming honestly — coumarin carries modest concerns at concentrated intake, hydroquinone and its glycoside arbutin attract caution, and tannins in quantity are strongly astringent — but these are the footnotes to a broadly gentle group.
Browse all phenolics in the filterable index ›
Flavonoids (116)
The flavonoids are a vast, near-ubiquitous family of polyphenol pigments sharing a fifteen-carbon two-ring-and-bridge skeleton, found throughout the plant kingdom in leaves, flowers and fruit. They are prized for antioxidant, anti-inflammatory and vaso-protective activity and are among the most benign of all plant constituents. Familiar examples include quercetin, rutin and hesperidin.
Anthocyanins (11)
Anthocyanins are the water-soluble flavonoid pigments responsible for most red, purple and blue colouring in flowers and fruit, shifting hue with acidity. They are widespread in berries and are noted for strong antioxidant and capillary-protective effects, with an excellent safety record as ordinary dietary pigments. Cyanidin and malvidin are representative molecules.
Flavanols & Proanthocyanidins (23)
The flavanols, or flavan-3-ols, comprise the catechins and the condensed tannins (proanthocyanidins) built from them. They are abundant in tea, cocoa, grape seed and many barks, and act as robust antioxidants that are generally very well tolerated. Epicatechin and epigallocatechin gallate (EGCG) are the classic examples.
Isoflavones (16)
Isoflavones are flavonoids in which the ring arrangement gives the molecule an oestrogen-like shape, making them the best-known dietary phytoestrogens. They are concentrated in legumes such as soya, red clover and liquorice, and are largely well tolerated, though their oestrogenic character invites a measure of care. Genistein and daidzein are the principal members.
Chalcones (5)
Chalcones are open-chain flavonoids that serve as the biosynthetic precursors to the closed-ring flavonoid pigments, and they often appear as yellow colouring in petals. They are relatively minor but widespread, and are studied chiefly for anti-inflammatory and antioxidant activity with no notable toxicity as a group. Isoliquiritigenin and xanthohumol are examples.
Tannins (15)
Tannins are large astringent polyphenols — either hydrolysable (gallo- and ellagitannins) or condensed — able to bind and precipitate proteins, which is the basis of their tissue-tightening, toning action. They are extremely common in bark, leaf and unripe fruit and are useful in moderation, though very high intakes are markedly astringent and can hinder mineral and protein absorption. Tannic acid and ellagitannins are typical.
Phenolic Acids (68)
Phenolic acids are among the simplest phenolics: single aromatic rings bearing carboxylic-acid or aldehyde groups, ubiquitous across herbs, coffee and culinary plants. They are gentle, dietary-level antioxidants with anti-inflammatory tendencies and no meaningful toxicity in ordinary amounts. The group includes caffeic, rosmarinic, chlorogenic and salicylic acids.
Coumarins (22)
Coumarins are fragrant benzopyrone compounds — the sweet, hay-like scent of dried grass and woodruff — with antispasmodic, vaso-protective and, in modified forms, anticoagulant activity. They are common in grasses, citrus and umbelliferous plants and are generally well tolerated, though simple coumarin carries moderate concern at concentrated intake. Coumarin and umbelliferone are representative.
Lignans (32)
Lignans are dimers of phenylpropanoid units, widespread in seeds, grains and woody tissue, and valued for antioxidant, hepatoprotective and phytoestrogen activity. They are on the whole gentle and well tolerated. Secoisolariciresinol from flaxseed and the silymarin complex of milk thistle are well-known examples.
Stilbenes (7)
Stilbenes are defensive polyphenols produced by plants under stress, structurally two aromatic rings joined by a short bridge. They are relatively uncommon but much studied, resveratrol from grape and Japanese knotweed being the standout, investigated for cardiovascular and longevity effects and generally regarded as benign. Pterostilbene is a related member.
Anthraquinones (17)
Anthraquinones are coloured three-ring phenolic compounds whose glycosides stimulate bowel motility, making them the active laxative principle of senna, cascara, rhubarb and aloe. They are effective but the one clear phenolic subgroup to use with restraint, since habitual or heavy use is purgative and irritating to the gut. Emodin, aloe-emodin and sennosides are the key molecules.
Quinones (24)
Quinones are reactive ring compounds — benzoquinones and naphthoquinones — formed by the oxidation of phenols, and their reactivity gives some of them pigmentary, antimicrobial or irritant character. They are moderately common, and while many are useful the more reactive members warrant caution. Juglone from walnut and the hydroquinone released from arbutin are examples.
Phenylpropanoids (67)
Phenylpropanoids are aromatics derived from cinnamic acid on a characteristic nine-carbon scaffold, forming a broad and abundant group that underlies many aromatic and medicinal constituents. They are largely well tolerated at culinary and medicinal doses. Examples span eugenol of clove, anethole of anise, the kavalactones of kava and the verbascoside-type glycosides.
Curcuminoids (4)
Curcuminoids are the yellow diarylheptanoid pigments of turmeric, two phenolic rings linked by a seven-carbon chain. Uncommon outside their botanical source, they are potent antioxidants and anti-inflammatories that are very well tolerated. Curcumin is the principal molecule, accompanied by demethoxy- and bisdemethoxycurcumin.
Other Phenolics (9)
This catch-all gathers phenolics not assigned to a defined subgroup — generic “phenolic compounds” and mixed polyphenols, along with simpler ring molecules such as the cardanol and cardol of cashew.