Possible side effects of witch hazel include minor skin irritation when applied topically and stomach upset when taken by mouth, according to WebMD. Large doses of witch hazel may lead to liver problems.
Although witch hazel contains safrole, a cancer-causing chemical, the amount contained in the herbal remedy is too small to be concerning, confirms WebMD. Individuals who are pregnant or breastfeeding should avoid witch hazel as there is not enough evidence to support its safety as of 2015. The tannins in witch hazel can help fight bacteria, repair damaged skin and relieve swelling when applied to the skin. However, the herb's high tannin content means patients should avoid internal use as the toxicity of these substances is not yet well established, according to Drugs.com.
When using witch hazel water for anal disorders such as hemorrhoids, patients can safely apply the remedy after bowel movements or up to six times a day, states WebMD. Witch hazel may also be effective for minor bleeding and mild skin irritation, but research does not support the herb's effectiveness in treating moderate eczema. Although witch hazel is possibly safe for children when applied topically, individuals should consult with a health care professional before using the herb on younger patients.