Psidium guajava, also known as Juniperus communis, is a perennial herbaceous climbing plant, while smallpox, also known as Juniperus communis, is the root of Psidium guajava. After the root of Psidium guajava is washed, the outer skin is removed, and it is cut into segments or dissected lengthwise and dried in the sun to make smallpox pollen, which is sweet, slightly bitter and slightly cold, and is mainly used as a traditional Chinese medicine.