According to the Qur’an, a true Muslim should refer to scholars to become well acquainted with the sound image of Islam. First of all, it should be clear that Hijab is meant to preserve Muslim woman’s dignity. Like all other Shari`ah-based commands, Hijab should be given due care, for it brings about countless fruits and wards off evils.

We’d like also to clarify that head covering is only a part of Hijab. Hijab is the dress code for Muslim women. Here are the requisites of hijab or proper Islamic attire for women:
1. It should cover her whole body except face and hands.
2. It should be loose-fitting.
3. It should not be transparent or revealing.
4. It should not be an attire specifically worn by men only.

Sheikh Ahmad Kutty, a senior lecturer and an Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states:
“Hijab is the proper Islamic dress code, which is primarily intended to safeguard the modesty, dignity and honor of men and women. Allah, the Creator of humans, knows our nature better than ourselves, and thus He has prescribed appropriate rules of behavior and appearance to be observed when men and women interact with one another in a social milieu. These rules of interaction also include a prescription for modest dressing, which, I should hasten to add, apply to males as well as females.
Hijab thus forms part of a holistic program of Islamic ethics and morals governing male and female interaction. Prescribing the rule of Hijab, Allah says, “Say to the believing men to lower their gazes and guard their chastity,” (An-Nur: 30) “And say to the believing women to lower their gazes and guard their chastity, and let them not display of their charm – except what is apparent.” (An-Nur: 31)
Commenting on the phrase, “what is apparent”, Ibn `Abbas, the famous Companion and the Qur’an exegete, said, “It means face and hands.” In other words, according to Ibn `Abbas, a woman must cover all her body except her face and hands while in the presence of men who are not related to her directly (and the list of those in whose presence she need not cover is clearly outlined in Surat An-Nur: 31).
the majority of Imams – including those of the Four Schools as well as others – share the above interpretation of Ibn `Abbas, and thus hold the opinion that a woman is not obliged to cover her face and hands.
In light of the above, we conclude: a Muslim woman is required to cover all her body except her face and hands, according to the majority of scholars belonging to all schools. Covering the head, however, is not at all a disputed issue among them – they all agree that this is a necessary part of Hijab.
A very important point has to be made here (concerning the point you raised in your question) as it is seldom mentioned in discussions on Hijab. Unfortunately, the onus of guarding the honor and chastity of the Muslim society is often laid solely on the backs of women. While recently, there has been more of a stress on the rules of Islamic dress for men, what needs to be addressed is the requirement of Muslim men to lower their gaze and maintain Islamic decorum in relations with all women – and not just Muslim women. It is not rare to see a Muslim couple walking where the woman is in full Hijab while her husband is gawking at other women, or to see a father instructing his daughter to cover properly before going out, and then turning back to watch a TV show full of improperly attired women. There is wisdom in the Qur’anic injunction to women to cover themselves, and this stated alongside the order to men to lower their gaze. Allah is Just and justice would not be served if women were to be the only guardians of honor.
the Hijab can become a tool of oppression if Muslim males do not maintain their part of this balance. It is often stated that it is difficult for Muslim men to avert their gaze and interact in business-like-ways with women in a society where such behavior is considered anti-social. To this we can answer that it is just as difficult or even more so for a Muslim woman to maintain Hijab in such a society. These tasks can be a struggle and Muslim males and females should view their respective duties as a social responsibility as well as acts of worship. As Allah states in the last part of the verse on Hijab, “O you who believe, turn ye altogether towards Allah in repentance that you me be successful.” (An-Nur: 31)”

Regarding the rationale behind hijab, we’d like to furnish you with what the American Muslim scholar, SheikhYusufEstes, Director of islamtomorrow.com, and National Chaplain WAMY, stated in this regard:

“Jewels ArePrecious– So Protect Them
When someone has a jewel or any precious item one always treats it with great respect and protects it against any loss. One may even build a special place to keep it or place it in a vault for security. Perhaps one may even hire a guard to insure that it will not be stolen. These things are most obvious to all of us and nothing here seems strange at all.
By the way, someone may say, ‘Why do we compare women to jewels and pearls? Doesn’t this sound as describing women as objects or mere possessions in this world?’
In reply to that, I say: Comparing women to jewels and pearls doesn’t mean that women are mere objects or worldly possessions. The intended item or object here is what the woman possesses, as mentioned by Allah in His Book. Allah is ordering us to tell the believing woman to lower her gaze and to protect her, guard her private parts and protect her chastity. She is being well advised by her father, brother, husband, son and all of us, to cover herself.
Somehow we have been deluded into thinking that women exhibiting their beauty in front of others and men encouraging this is warranted. Many large corporations protect their shareholders from losses while at the same time producing cosmetics, jewelry and clothing that do exactly the opposite for our ladies. Money and vain desires are the primary reasons for this type of exploitation in the world today.
It should be that we would be asking the question: ‘Why are women exposed in public in a way that men do not even see them in the privacy of your home?’ The problem today is that society is so far away from the basic concepts of moral and correct behavior that was originally ordained by the Almighty Lord of the Universe (Allah). As each year passes, we see more and more deviation away from the proper attire and behavior in public. Fashion designers, cosmetic companies and women’s magazines make huge fortunes selling the poor beguiled women on the idea of presenting themselves as if on display in a market for others to stare at them and then decide how they ‘rate.’
So actually, Islam has been preserving the correct and proper dress code, not only for ladies, but for men as well. In addition to defining the proper attire for the sexes, Islam also carefully instructs both men and women on how to behave toward each other. For instance the Qur’an tells us in surat An-Nur in verses 30 and 31 exactly how to act in the presence of the opposite sex: (Tell the believing men to LOWER THEIR GAZE…) And then (Tell the believing women to LOWER THEIR GAZE…)
So, immediately we understand that it is more than just the clothing that is desired. It is the proper respect and behavior of the two sexes toward each other at all times. Keep in mind that Islam is not just another religion. Islam (Total Surrender, Submission, Obedience, Sincerity and Peace with Allah) is for all people, in all places and in all times.