Skin boil refers to skin texture, which is a barrier outside the human body. See Liu's On Ji Da. "The Yellow Emperor's Internal Classic Su Wen Liu Jacky Ji Da Lun": "The cold reaches the body, the gentleman is biting, and the people are sick."
For details, please refer to the encyclopedia entry: Pi Pi[ last modified at 2016/1/216:17: 08 * * 63], and automatically match the following results. Please identify for yourself.