Surah An-Nur, Verses 30 and 31

'And Say to the believing women to lower their gaze (from looking at forbidden things), and protect their private parts (from illegal sexual acts) and not to show off their adornment except only that which is apparent (like both eyes for necessity to see the way, or outer palms of hands or one eye or dress like veil, gloves, head-cover, apron), and to draw their veils all over Juyubihinna (i.e. their bodies, faces, necks and bossoms) and not to reveal their adornment except to their husbands, or their fathers, or their husband's fathers, or their sons, or their husband's sons, or their brothers or their brother's sons, or their sister's sons, or their (Muslim women) (i.e. sisters in Islam), or the (female) slaves whom their right hands possess, or old male servants who lack vigour, or small children who have no sense of feminine sex. And let them not stamp their feet so as to reveal what they hide of their adornment. And all of you beg Allah to forgive you all, O believers, that you may be successful'

It is apparent that upon a plain reading the purpose of the verse is to eradicate promiscuity, fornication and adultery and all the preliminary steps that lead directly to the commission of such shameful acts. The references to 'lowering their gaze', 'drawing their veils over their bosoms' and 'striking their feet to draw attention' indicate that all acts or omissions which in the ordinary course leads directly to sexual promiscuity and FITNAH are forbidden.

In order to totally eradicate sexual promiscuity and FITNAH, the verse goes on to say that a woman is not permitted to display her beauty and charms except in degrees to her husband, father and the other classes of person specified in the verse. The exempt class would constitute the MAHAARIM, and any other would qualify as strangers or GHAIR MAHRAM. The principle fixed by the verse is, therefore that a woman cannot display her beauty to any male person other than the persons exempted by the verse. It goes without saying that the face is the focal-point of a woman's beauty, and the main source of attraction. Hence, the face of a woman cannot be displayed or shown to a stranger in normal circumstances whether in public or private according to the general principle fixed by the verse as stated above. She is permitted to display her beauty to the exempt class (the MAHAARIM) for obvious reasons of close contact, and because of the considerably lesser danger of sexual promiscuity and FITNAH within that class. (Zamakhshari)

The Shariáh, however, is practical, dynamic and takes into account the real situations of life. A woman may in the case of genuine need be forced to expose her face in the presence of strangers. For example, when she appears in court to give witness, etc.

It is against this background that the preceding portion of the verse 'they should not display their beauty and charms except what must ordinarily appear unavoidable' falls into proper perspective. The words 'Illaa maa dhahara min'haa' are in context an exception to the general rule, and cover those cases of genuine need and necessity when a woman is forced to expose her face in the presence of a stranger. That is how the great commentators of the Noble Qurãn have interpreted the verse.

Take the following two examples,

'Women must not display any part of their beauty and charms to strangers except what cannot possibly be concealed.' (Ibn Katheer)

'Why is the woman permitted to display her external beauty and charms? Because to conceal that would cause her inconvinience. A woman is forced to deal in commodities with her own hands. She is compelled by genuine need to expose her face especially at the times of giving evidence, litigating in court and marriage. She is compelled to walk the streets and expose her feet, especially poor women. This is the meaning of 'illaa maa dhahara min'haa' that is 'except what the situations of ordinary life compel her to expose'. (Zamakhshari)

A further point is the interpretation of 'illaa maa dhahara min'haa' has been highlighted by the well known scholar, Moulana Ashraf Ali Thanwi (RA). He states that the verb used is that of the first form 'dhahara' and not 'adhhar' which in forth form signifies a deliberate exposure or display. The use of 'maa dhahara' indicates that the exposure of the face is confined to need. (Imdaadul Fataawa vol. 4 p. 181)

It follows from the aforegoing that upon a proper interpretation of the verse the face and hands of a woman can only be exposed to strangers in a situation of genuine need where concealment would cause her serious inconvinience. 

However, genuine need is not open to wide interpretations.

SURA AL-AHZAAB - VERSE 53

'...And when you ask them for anything you want, ask them from behind a screen...'

The meaning of this verse is clear: the companions of the Holy Prophet (Sallallaahu Álayhi Wasallam) were ordered to communicate with the wives of Rasulullah (Sallallaahu Álayhi Wasallam) from behind a screen and not directly face to face. It is obvious that this instruction is not limited to the wives of the Holy Prophet (Sallallaau Álayhi Wasallam). The verse has general application and the fact that the noble wives of Rasulullah (Sallallaahu Álayhi Wasallam) are specifically mentioned emphasises the importance of the subject matter. The distinguished jurist, Abubakar Jassa (RA) in his Ahkaamul Qurãn states:

'This order, although revealed specifically in relation to the Holy Prophet (Sallallaahu Álayhi Wasallam) is general in application because we are ordered to follow him.'

Similarly, the well known commentator of the Noble Qurãn, Imaam Qurtubi (RA) in his Al-Jamia li Ahkaamul Qurãn states:

'All women are in effect covered by the terms of the verse which embraces the Sharée principle that the whole of a woman is 'Áwrah' (to be concealed) - her body and voice, as mentioned previously. It is not permissible to expose those parts except in the case of need, such as the giving of evidence...'

SURAH AL-AHZAAB - VERSE 59

'O Prophet! Tell your wives and your daughters and the women of the believers to draw their cloaks (veils all over their bodies (i.e. screen themselves completely except the eyes or one eye to see the way)...'

In his commentary to this verse, Allama Abubakar Jassas (RA) states the following:

'This verse proves that a young woman is ordered to cover her face from strangers, and to manifest SATR and modesty in public so that doubtful people may not be desirous of her.'

It is sufficient to quote the following authentic commentators in their interpretation of the verse:

'They (women), shall cover their faces and bodies with their outer garment when they appear in public for a valid reason.'

'They shall cover their faces and...'

Ibn Ábbaas (Radhiallaahu Ánhu) states that the Muslim women are ordered to cover their head and faces with outer garments except for one eye.'

And Allah Taãla Knows Best

Why Women Should Wear the Veil?

Women throughout the world spend millions of Dollars on facial beauty. Companies manufacturing 'beauty' products make a colossal figure in sales. It would be nothing short saying that the products used on the face far exceed other products. This in itself proves that humans are particularly possessive of their looks - facial expression. People especially women take great pride and time in making up their faces. Allah Ta'ala has placed the beauty of man and woman in the face. Perhaps the busiest part of the body is the face - used extensively in communication. The face communicates the person's mood and facial expressions and expresses the character and mannerism. Because so much of identification is assembled by the face, least to mention the beauty of women, Muslim women are required to hide away their beauty. The veil forms part of their concealment.

[Source: Jamiatul Ulama (KZN)] 

http://www.shariahprogram.ca/islam-qa-women/hijab-face.shtml