why you need polyphenols in your skincare

My philosophy of skin care formulation is to use plant extracts for specific needs. My first experiment was in creating a hair oil infused with hibiscus flowers, amla (gooseberry) and rosemary leaves. The next inspiration for a plant extract came after I unseeded a pomegranate fruit (from a local farm) and was left staring at the peels. I decided to dry them and spent the next few weeks researching pomegranate peels. My research led me to getting to know a class of compounds called polyphenols quite intimately.

Phenols are a class of aromatic compounds (containing a benzene ring and a hydroxy group). 

It turns out that pomegranates (fruit, peels, roots etc), white oak bark and several other plant materials are rich in polyphenols - compounds that have multiple phenol structural units. Below is a further classification of different types of polyphenolics which have different benefits for skin:

Pic courtesy: https://www.researchgate.net/figure/The-classification-of-phenolic-compounds_fig3_295082287
​One of the key properties of polyphenols in general is their exceptional antioxidant properties. They are fantastic scavengers of reactive oxygen species that are generated in our tissues when exposed to harmful UV rays from the sun and lead to various skin disorders, including in the extreme, skin cancer. There are a multitude of other benefits as well as shown in the picture below:

Reference for picture above.
My primary interest is to see how polyphenol topical application can help with skin issues. The picture above indicates the mechanisms by which these compounds can help against aging - photo protection, cell renewal, inhibition of melanin (suppress age spots, melasma?), collagen stimulation, constriction of blood vessels (under-eye dark circles).
One of Saroya Natural's most popular products is the Blemish Control Botanical Serum, containing extracts of three botanicals, pomegranate peel, white willow bark, and Baluchi seed. Pomegranate peel extract is rich is polyphenolic acids (punicalagin acid, ellagic acid) that have photo protection benefits and also rich in tannins which aid skin cells renewal. In other words, perfect for use in an anti-aging product!
The white oak bark extract is rich is quercetin and tannins - which can help with blood vessel constriction and melanogenesis inhibition - i.e. an under-eye dark circle treatment.
Bakuchi seeds are a source of several polyphenols. An example is bakuchiol, an ingredient that has come under the limelight for firming aging skin and helping with acne prone skin. 
One of the challenges with using concentrated amounts of polyphenols is extraction and delivery. A serum or oil is the best medium. To learn about botanical rich oils, read this post.