The foreskin refers to a layer of skin wrapped around the penis head. When you open the foreskin, you can see that the ring-shaped narrowing behind the glans penis is called the coronal groove. There are many sebaceous glands in the skin near the coronary sulcus, which secrete a smelly secretion, which is yellow and white mud-like, called "skin scale".

Phycosis means that the foreskin mouth is too small, so that the foreskin can not be turned up to expose the penis head; If the foreskin is too long, it means that the foreskin covers all the penis heads, but the foreskin mouth is not small, and the penis heads can be turned over.