Commonly used plant extract that can have potent antioxidant properties and some soothing properties. However, witch hazel’s high tannin content (tannin is a potent antioxidant) can also make it sensitizing if used repeatedly on skin. The bark of the witch hazel plant has a higher tannin content than the leaves. Producing witch hazel water by steam distillation removes the tannins, but the plant’s astringent qualities are what most believe give it benefit.
Alcohol is added during the distillation process, the amount typically being 14–15%. Witch hazel water is distilled from all parts of the plant; therefore, you never know exactly what you’re getting, although the alcohol content remains.
Depending on the form of witch hazel, you’re exposing your skin either to an sensitizing amount of alcohol or to tannins, or both. Moreover, witch hazel contains the fragrance chemical eugenol, which is another source of sensitivity.
References for this information:
International Journal of Trichology, July-September 2014, pages 100-103
Chemical Research in Toxicology, March 2008, pages 696-704
Skin Pharmacology and Applied Skin Physiology, March-April 2002, pages 125-132
Phytotherapy Research, June 2002, pages 364-367
Journal of Dermatologic Sciences, July 1995, pages 25-34
Journal of Inflammation, October 2011, page 27