External use refers to drugs directly applied to the skin or scattered in the surrounding environment, so it is not an oral drug.

Shuang has a long history and is a famous time-honored medicinal material. It has been sold all over the world since 1838. 1838, Henry Ricqles, a pharmacist, created a medicinal liquid, Shuang Ren Fei, on the basis of mint and ethanol, and put forward the trademark of Shuang Ren Fei, but it really started to be used in 1857.