Phenols are chemically active compounds found in plants, with a hydroxyl functional group bonded to an aromatic ring. They have a wide range of properties, including health benefits and toxicity. Polyphenols, found in many plant sources, have antioxidant properties and can reduce the risk of heart disease and cancer. However, some phenols are harmful, such as urushiol in poison ivy and carbolic acid. Phenols have a variety of effects on biological pathways in humans and animals.
A phenol is one of several chemically active compounds found in nature, especially in plants. Their molecules each include a hydroxyl (OH) functional group bonded to the ring of an aromatic compound, a molecule that includes at least one ring of carbon atoms. Phenols exhibit a wide range of properties; some are heralded for their health benefits, while others are deadly poisons. Some have important industrial uses as drugs or food additives. The word phenol can also refer to carbolic acid (C6H5OH), the simplest of this group of chemicals.
The category of phenols is chemically similar to alcohols, but phenols form stronger hydrogen bonds with other chemical compounds. They are also distinguished from alcohols by their higher acidity, solubility, and boiling points. Most are colorless, although some are brightly colored and play an important role in plant pigmentation. They are usually solid or liquid at room temperature.
There are hundreds of different types of phenols and these contribute to the variety of plant life on earth. Some, such as anthocyanins and flavonoids, provide coloration. Others, such as eugenol and ketol, provide flavors. Phenols also exhibit a wide variety of effects on biological pathways in humans and other animals. These include everything from capsaicin, which makes chili peppers hot, to cannabinoids, the active ingredient in marijuana. The anesthetic propofol, the antiseptic xylenol, and salicylic acid, a common acne medication, are each a phenol.
Many of the ones that are important to human health are polyphenols, chemicals made up of several phenol molecules chained together. This group includes tannins, lignins and flavonoids. Some polyphenols, such as tyrosol and oleuropein, are believed to have antioxidant properties. Others can reduce the likelihood of heart disease or cancer. At least one polyphenol, resveratrol, is thought to have powerful anti-aging effects.
Polyphenols are found in olive oil, fruit peels, leaves, berries, tea, coffee, chocolate, nuts and a number of other plant sources. Many are found in wine, especially red wine, where they contribute a lot to taste and color. Some have been extracted and made into dietary supplements. Because so many health benefits have been associated with these compounds, some people are quick to attribute other, less established benefits to them. Not all claims have solid science behind them; buyer beware.
Some phenols are actually harmful to health. Many plants secrete unpleasant or poisonous phenolic compounds to discourage herbivores. One, urushiol, causes the rash associated with poison ivy and poison oak. Tannins give acorns their bitter taste and are poisonous in high doses. Carbolic acid causes chemical burns and can be carcinogenic. In short, because the category includes a wide variety of chemicals, it also includes a wide variety of human health effects.
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