Human penis
The foreskin is a fold of skin that covers the end of the penis. The foreskin is a bit thicker than an eyelid. Cutting off the foreskin is called circumcision. The foreskin is connected to the head of the penis. During circumcision, most or all of the foreskin is removed from the penis. This simple change to the penis is very common in many countries of the world including the United States and Israel.  Circumcision is done for medical reasons because it lowers the chance of ever getting cancer of the penis to near zero. The foreskin removed during circumcision is a possible source of penile cancer. Childhood circumcision has a strong protective effect against penile cancer in later life. Penile cancer has been nearly eliminated in populations of males circumcised shortly after birth. Circumcision virtually eliminates the risk of invasive penile cancer. Being uncircumcised is a risk factor for penile cancer. Invasive penile cancer is cancer that spreads in the body. It is uncommon but often causes the man to die. Circumcision also reduces the risk of cancer of the cervix in female sexual partners.  Cervical cancer is very common. It causes over 300,000 deaths of women worldwide every year. Circumcision reduces, but does not eliminate, the risk of getting or spreading HIV/AIDS. Circumcision became more common in Africa after HIV/AIDS began. The use of condoms also reduces the risk of getting or spreading HIV/AIDS, but many people in Africa cannot afford condoms or choose not to use them.