It is the general consensus among the Muslims that a Muslim woman is required to cover her head leaving only her face showing as part of an overall dress code and behaviour which Islam prescribes. It is therefore part of the social system of Islam, and a manifestation of important general Islamic principles. Firstly, an educated Muslim woman does this because she is following guidance from God and His prophet Muhammad recorded in the Qur'an,and in the Sunnah (the knowledge about the practice and example of the Prophet Muhammad (peace and blessings be upon him)). For example, one translation of the meaning of the specific ayat (verse)of Qur'an that mentions the head covering is as follows:

Surah 24 Al-Nur (The Light); ayat 31 (part of)

And say to the believing women……that they should draw their head-coverings over the neck opening (of their dresses) , and not display their ornaments except to their husbands, their fathers…..(etc)

This guidance she regards, as by definition a Muslim should do, as being revealed by the 'All-Knowing' the 'Most Wise', The 'Most Merciful', 'All-Mighty' God who created all human beings and whose Power controls everything. She is doing it because she believes that God with His nature knows best what is in the true best interests of human beings, far more than a human can know, with his or her fallibility, and weaknesses.

The main principle reason for the hijab is modesty, which is not wishing to receive unnecessary attention from people, such as admiration and flattery, envy, or, most importantly, sexual attraction from those other than her husband.Great care is taken to keep sexual thoughts, feelings and interactions to within the boundaries of the marital relationship.

These types of attention may boost the 'ego' for the short term, but all have the potential to lead to disastrous consequences in the long term, for example leading to confused feelings, competition, suspicions, affairs, break-up of marriages and other relationships, disturbed children, and ultimately a community where people are insecure,unhappy, and divided amongst themselves.

From this it can be seen that the hijab is a manifestation of another important principle in Islam, which is valuing benefits which are permanent above those which are temporary. What is permanently beneficial is, for example, a happy marriage between two people who aim to learn, teach and apply Islam to the best of their ability in their lives. This is seen as that which brings about the true happiness of the soul for eternity, by purifying and keeping it in its pure, natural, God-created state, filling it with peace and contentment, patience, gratefulness, love and compassion. What is temporary are the momentary pleasures derived from, for example, people's opinions of you, leading to your own self-satisfaction, or, even more basically, those derived from physical sensations.

A strong marriage, and a peaceful, cooperative, happy community, where people's feelings towards one another are good, will not only provide the true happiness that the soul needs, but also, in moderation, the good opinion, physical, and other pleasures that the ego requires.

Therefore, the freedom and benefit of the soul is encouraged, requiring a corresponding disciplining and moderating of the ego, but not a total denial or repression of it.

Besides following modest dress codes appropriate to the different natures of a man and woman, both Muslim men and women should abide by a certain modest and respectful code of conduct when interacting with the opposite sex.

http://www.islamic.org.uk/hijab.html