Internal use of horse chestnut seed extracts standardized for aescin at recommended amounts is generally safe. However, in rare cases oral intake of horse chestnut may cause itching, nausea, and upset stomach.¹¹ Based on reports of worsening kidney function in people with kidney disease who received intravenous aescin, horse chestnut should be avoided by anyone with kidney disease.^{12, 13} People with liver disease should also avoid the use of horse chestnut. There are no known reasons to avoid horse chestnut during pregnancy.¹⁴ Topically, horse chestnut has been associated with rare cases of allergic skin reactions. Circulation disorders and trauma associated with swelling may be the sign of a serious condition. Therefore, a healthcare professional should be consulted before self-treating with horse chestnut.