As an aside, polyphenols are found in pretty much every fruit and vegetable out there. We'll take a look at various polyphenols in depth in the oil or extract specific posts.
There are over 4,000 identified flavonoids - you may see them as flavenols, flavones, isoflavones - and I'm not going into all of them on this blog! The ones containing ketones, like flavonoids and flavonals, are potent anti-oxidants with anti-allergic, anti-inflammatory, and anti-microbial benefits for your skin, and work as anti-oxidants for the purposes of preventing rancidity.
Flavonoids behave as anti-oxidants on our skin and in our bodies by scavenging the free radicals produced at our cell membranes. It is thought (meaning there aren't enough studies or nothing conclusive) the flavonoids offer anti-inflammatory benefits by inhibiting pro-inflammation mediators in our bodies, such as prostaglandins.
Catechins (a type of flavonoid) found in tea and chocolate can offer anti-biotic properties in our products as they disrupt a stage of bacterial DNA replication. This isn't to say you can use tea or chocolate (or extracts like cocoa butter or green tea butter) as a preservative for your lotions, but that's a nice thing in a lotion! A type of catechin found in green tea is being investigated for its role in preventing UV related skin damage.
Lignans behave as anti-oxidants and phytoestrogens in our body. We find the lignans in flax seed (0.3 grams per 100 grams), sesame seed (29 mg per 100 grams), pumpkin, and soy bean oil. The lignan sesamine found in sesame oil has been shown to be immuno-suppressive in lab tests, but not on humans.
As a note, isoflavones, like those found in soy bean products, can behave as phyto-estrogens as well. Neither the lignan nor the isoflavone phyto-estrogens behave this way when applied to skin - they have to be ingested to get that effect. (But who knows what science will discover next? Perhaps we're not applying them in high amounts?)
Tannins are water soluble phenolic compounds found in grapes, tea, and other botanical ingredients. They tend to be very astringent and produce "dry" oils like grapeseed, hazelnut, and camellia oil. (An astringent is defined as a substance that contracts the pores and tissues and makes them smaller). Witch hazel and green tea extract contain high levels of tannins, hence their notoriety for astringency.
The various polyphenols we use in skin care products are only just now being investigated in any great depth - this is why you're seeing the ingredient of the month touted by all the big companies and being good for x or wonderful for y! Polyphenols found in olive oil have been studied extensively, and they have been shown to help repair sun damaged skin. And studies coming out now about sea buckthorn oil show it may also have regenerative properties.
Polyphenols tend to lend a bitter taste to their fruits and vegetables - and in skin care products, they tend to produce oils that are "drier" than other oils and offer astringency. There tends to be a correlation between the amount of polyphenols and that slippery feeling in a lotion. Oils with high tannin levels - camellia oil, for instance - feel drier on our skin and can be more astringent. As a result, we might not want to use high polyphenolic oils as our primary oils if we want something glidy and slidy.
Join me tomorrow when we resume our posts on the oils - specifically, soy bean oil!