It's the extract from the silver-white bark of the Birch tree that grows on moors in North and Middle Europe and in North America. It contains tannins and triterpenes that give the extract antioxidant, anti-irritant and astringent magic properties.
There is also research showing that birch bark extract can improve the skin barrier, increase skin hydration and reduce trans-epidermal water loss. Can be a useful ingredient both for dry and oily skin.
- Skin pharmacology and physiology, 2011;24(6):289-93. 2011 Jun 25., Dermocosmetics for dry skin: a new role for botanical extracts.