Zoe K says…How do tannins found in witch hazel act as an astringent? And how is witch hazel modified from its original state to its state in cosmetics?
The Right Brain responds:
After reading the StevenFoster educational monograph we’re now equipped to tell you more than you ever wanted to know about witch hazel.
First, we’ll explain that astringents are materials that give the skin a feeling of tightness. In the case of witch hazel the active ingredient is a chemical called a tannin. (At the time of this writing it’s close to Christmas, so I’m tempted to work in some kind of pun about a “tannin bomb.” But I won’t.) Anyway, tannins can cross link proteins causing biological structures like skin to literally “tighten up.” (Note: sometimes alcohol evaporation can give this impression.)
In its natural form witch hazel is a shrub that can grow to be 10 feet tall, or more. It has oval leaves and slender petals. In autumn, the plant is harvested by cutting the branches to the ground and chipping the wood and leaves into little bite size pieces. This mulch is then transferred to large stainless-steel vats where it is steam distilled for thirty-six hours. After “stewing” the extracted mixture is condensed and filtered and ethanol is added as a preservative. (Depending on the exact processing, the witch hazel may contain more or less tannins. The mixture of plant parts also controls the tannin content – bark contains 31 times more tannin than the leaves.) The resulting liquid is bottled and sold to drug stores as “witch hazel.”