In ayah 31 of sura Nur, and in many traditions, the limitations of hijab have been made clear.in this ayah Allah states: And tell the faithful women to cast down their looks and to guard their private parts, and not to display their charms, except for their husbands, or their fathers, or their husband’s fathers, or their sons, or their husband’s sons, or their brothers, or their brothers sons, or their sisters’, or their women or their female captures, or male dependants lacking [sexual] desire, or children initiated to women’s parts[i]. And let them not thump their feet to make known their hidden ornaments. Rally to Allah in Repentance, O faithful, so that you may be felicitous. In “Usul Kafi” numerous hadiths have been mentioned on the limitations of hijab, which have been collected and put under the following section: Parts of a woman permissible to look at. Masadeh Ibn Zararah narrates a tradition from Imam Sadiq (Peace be upon him). He asked the Imam about the beauties that a woman can reveal. He answered, “The face and the palms of the hand”. Of course, from an Islamic perspective, being allowed to show the face is dependant upon the condition that it is without makeup or it is with very minor makeup, such as plucking eyebrows or cleansing and shaving the face (which in some cultures is not consider makeup).
[i] Holy Quran, Sura Nur ayah 31
Hijab and the covering of women is so important that Allah has made reference to it in the honorable Quran. In sura Nur Allah has states: And tell the faithful women to cast down their looks and to guard their private parts, and not to display their charms, except for their husbands, or their fathers, or their husband’s fathers, or their sons, or their husband’s sons, or their brothers, or their brothers sons, or their sisters’, or their women or their female captures, or male dependants lacking [sexual] desire, or children initiated to women’s parts. Many believe that the face and the hands from the wrist down are exception from the rule, and there are indications of this exception in this ayah; such as:
- The exception of apparent beauty in this ayah, whether it denotes beauty itself or the place of beauty, is a clear explanation as to why it is not necessary to cover the face and hands.
- The meaning of the commandment of this ayah is another indication for this claim in regards to throwing the ends of a head-garb or covering over the collar-area; covering the whole head and neck and chest, yet it does not mention covering the face. History has also shown us that wearing a face-veil was not a public custom in the beginning of Islam.
In several traditions, the pure Imams (Peace be upon them) , in the exegesis of this noble ayah, have explained the amount of hijab tha is necessary and obligatory. Fuzail Yasar (one of the companion of Imam Sadiq (Peace be upon him)) said, I asked Imam sadiq (Peace be upon him), “Are the forearms (from the wrist to the elbow) of a woman one of the beauties included in those which Allah has stated that a woman should not reveal to any other than her husband?” Imam Sadiq answered, “Yes and the body parts which are lower than the head-garb are considered beauties…”
Also Masadah Ibn Zararah has narrated from Hazrat Imam Sadiq that when he asked the Imam about the beauties that a woman can expose [in public], he stated; “the face and the hands.”
Of course we must pay attention to two points:
- From an Islamic perspective, revealing of a woman’s face has no problem as long as it is without makeup, or with very minimal makeup (meaning it is not considered makeup by the common culture), and is not a cause of corruption.
- The instances which explained that the face and hands do not need to be covered do not indicate that there is nothing wrong with a man looking at them; because there is no necessity between the two, and here we have only discussed the first issue.
Note: in the occasion of revelation of this ayah, they have said that Arabs during that time wore head-garbs and covering, and they would throw the ends over their shoulders or on their backs, in such a way that the head-garb would be set behind their ears, and they would only cover their heads and the back of their necks. However, below the throat and some of the chest would be visible. Islam corrected this, and commanded them to use the ends of their head-garbs to cover their chest and collar area instead of just behind the ears or the back of the neck. The result was that just the roundness of the face would be visible and the rest of the body, covered.
 Nemuneh Commentary: Vol.14, Pg.450,451
 Using Hadith from Usul Kafi: Vol.5, Pg.521, Section "That of a Woman Which is Permissible to See"
 Wasa'ilu Shia Vol.20, Hadith No.25429, Pg.203, Section "That of a Woman Which is Permissible to Look at Without Lust"
 Replies to Religious Questions by Imam Khomeini (May Allah have mercy on his soul): Vol.3, Pg.256, Ques.33, 34;  Catechism of Imam Khomeini: Vol.2, Pg.929, Section "Women and the Revealing of Makeup".
 Hijab by Shahid Mutahari (May Allah have mercy on his soul):pages 164 - 235