Circumcision is a medical intervention, during which the foreskin is removed from the penis. This might either be necessary for a religious or medical reason. If the foreskin is removed, it does not cover the glans.
Circumcision for a religious reason
The most common religious reason of circumcision is the old custom among orthodox Jewish people to have this intervention done to every male child at the age of 8 days. Islam religion also requires circumcision as an act of obedience and commitment. For this reason, it is customary to have this intervention done to every male child. Other religions that require circumcision also exist, but the aforementioned two are the most common.
It is important to note that these old religious rules regarding circumcision have their roots in medical purposes as well. For instance, for people living in the desert, it was not easy to access proper hygiene, therefore, they wanted to prevent problems potentially arising from lack of water, through circumcision.
Circumcision for a medical reason
In terms of medical reasons, phimosis is the most common necessitating factor. Phimosis might be connate, but it might also develop later in life. It is a condition when the foreskin can only be partially withdrawn from the glans, or not at all. This provides hygienic problems as it makes it difficult to access the glans, which might lead to inflammation. This can be prevented by circumcision in these cases. Narrow foreskin can also cause problems in the sexual life. For this reason, partial phimosis is often only noticed when a man reaches the age when he begins his sexual life. Circumcision is not too late even then, if phimosis causes problems, it should be done.