Short answer
A mahram is a man a woman can never marry because of blood, breastfeeding or marriage ties: her father, grandfathers, sons, grandsons, brothers, nephews, uncles, father-in-law, son-in-law and stepson, among others. She may be seen without hijab by them and may travel with them. Cousins and brothers-in-law are not mahram.
A mahram is a man permanently forbidden to her in marriage by lineage, by milk (breastfeeding) or by marriage. In front of a mahram she may uncover her head, hair, neck, arms and lower legs, but not the area between the navel and the knees, nor the back and stomach. For travel, the mahram must be sane, past puberty and trustworthy.
Other madhhabs
- Shafi'i
- Milk kinship needs at least five separate feedings within the baby's first two years.
- Maliki
- Any amount of milk counts, as for the Hanafis, but only within about the first two years.
- Hanbali
- Milk kinship needs at least five separate feedings within the baby's first two years.
Explanation
The word mahram comes from haram, forbidden: he is a man whom you can never marry. The Quran lists the men a woman may show her adornment to, and the list of women forbidden in marriage gives the same family from the other side. The four schools agree on the list.
By blood:
- Father, grandfathers and great-grandfathers on both sides.
- Sons, grandsons and their sons.
- Brothers and half-brothers.
- Nephews: the sons of your brothers and sisters, and their sons.
- Uncles: your father's and mother's brothers, and the brothers of your grandparents.
By marriage: your father-in-law and his father, your son-in-law, your stepson (your husband's son from another wife), and your stepfather once he has consummated his marriage with your mother. See is father-in-law a mahram.
By breastfeeding: the Prophet ﷺ said that breastfeeding makes forbidden what lineage makes forbidden. So a man who is your milk father, milk brother or milk uncle is a mahram. In the Hanafi school this applies to feeding within the first two and a half years, and any amount counts.
Not mahram: cousins, your husband's brothers, your sister's husband, your husband's uncles and nephews, adopted sons and brothers who were not breastfed by your mother. In front of them, full hijab applies and being alone with them is not allowed. See the awrah guide for what may show in front of mahrams.
The evidence
Quran, Surah An-Noor 24:31
وَقُل لِّلْمُؤْمِنَٰتِ يَغْضُضْنَ مِنْ أَبْصَٰرِهِنَّ وَيَحْفَظْنَ فُرُوجَهُنَّ وَلَا يُبْدِينَ زِينَتَهُنَّ إِلَّا مَا ظَهَرَ مِنْهَا ۖ وَلْيَضْرِبْنَ بِخُمُرِهِنَّ عَلَىٰ جُيُوبِهِنَّ ۖ وَلَا يُبْدِينَ زِينَتَهُنَّ إِلَّا لِبُعُولَتِهِنَّ أَوْ ءَابَآئِهِنَّ أَوْ ءَابَآءِ بُعُولَتِهِنَّ أَوْ أَبْنَآئِهِنَّ أَوْ أَبْنَآءِ بُعُولَتِهِنَّ أَوْ إِخْوَٰنِهِنَّ أَوْ بَنِىٓ إِخْوَٰنِهِنَّ أَوْ بَنِىٓ أَخَوَٰتِهِنَّ أَوْ نِسَآئِهِنَّ أَوْ مَا مَلَكَتْ أَيْمَٰنُهُنَّ أَوِ ٱلتَّٰبِعِينَ غَيْرِ أُو۟لِى ٱلْإِرْبَةِ مِنَ ٱلرِّجَالِ أَوِ ٱلطِّفْلِ ٱلَّذِينَ لَمْ يَظْهَرُوا۟ عَلَىٰ عَوْرَٰتِ ٱلنِّسَآءِ ۖ وَلَا يَضْرِبْنَ بِأَرْجُلِهِنَّ لِيُعْلَمَ مَا يُخْفِينَ مِن زِينَتِهِنَّ ۚ وَتُوبُوٓا۟ إِلَى ٱللَّهِ جَمِيعًا أَيُّهَ ٱلْمُؤْمِنُونَ لَعَلَّكُمْ تُفْلِحُونَ ﴿٣١﴾
And tell the believing women to reduce [some] of their vision and guard their private parts and not expose their adornment except that which [necessarily] appears thereof and to wrap [a portion of] their headcovers over their chests and not expose their adornment except to their husbands, their fathers, their husbands' fathers, their sons, their husbands' sons, their brothers, their brothers' sons, their sisters' sons, their women, that which their right hands possess, or those male attendants having no physical desire, or children who are not yet aware of the private aspects of women. And let them not stamp their feet to make known what they conceal of their adornment. And turn to Allah in repentance, all of you, O believers, that you might succeed.
Lists the men in front of whom a woman may show her adornment.
Quran, Surah An-Nisaa 4:23
حُرِّمَتْ عَلَيْكُمْ أُمَّهَٰتُكُمْ وَبَنَاتُكُمْ وَأَخَوَٰتُكُمْ وَعَمَّٰتُكُمْ وَخَٰلَٰتُكُمْ وَبَنَاتُ ٱلْأَخِ وَبَنَاتُ ٱلْأُخْتِ وَأُمَّهَٰتُكُمُ ٱلَّٰتِىٓ أَرْضَعْنَكُمْ وَأَخَوَٰتُكُم مِّنَ ٱلرَّضَٰعَةِ وَأُمَّهَٰتُ نِسَآئِكُمْ وَرَبَٰٓئِبُكُمُ ٱلَّٰتِى فِى حُجُورِكُم مِّن نِّسَآئِكُمُ ٱلَّٰتِى دَخَلْتُم بِهِنَّ فَإِن لَّمْ تَكُونُوا۟ دَخَلْتُم بِهِنَّ فَلَا جُنَاحَ عَلَيْكُمْ وَحَلَٰٓئِلُ أَبْنَآئِكُمُ ٱلَّذِينَ مِنْ أَصْلَٰبِكُمْ وَأَن تَجْمَعُوا۟ بَيْنَ ٱلْأُخْتَيْنِ إِلَّا مَا قَدْ سَلَفَ ۗ إِنَّ ٱللَّهَ كَانَ غَفُورًۭا رَّحِيمًۭا ﴿٢٣﴾
Prohibited to you [for marriage] are your mothers, your daughters, your sisters, your father's sisters, your mother's sisters, your brother's daughters, your sister's daughters, your [milk] mothers who nursed you, your sisters through nursing, your wives' mothers, and your step-daughters under your guardianship [born] of your wives unto whom you have gone in. But if you have not gone in unto them, there is no sin upon you. And [also prohibited are] the wives of your sons who are from your [own] loins, and that you take [in marriage] two sisters simultaneously, except for what has already occurred. Indeed, Allah is ever Forgiving and Merciful.
Lists the relatives forbidden in marriage, which defines who is a mahram.
Sahih al-Bukhari 2645
Sahih... يحرم من الرضاع ما يحرم من النسب ...
"Breastfeeding makes forbidden what lineage makes forbidden."
Shows that milk relatives become mahram just like blood relatives.
Where the ruling is recorded
- al-Hidaya, Kitab al-Nikah, chapter on women forbidden in marriage. The categories of permanent prohibition by lineage, marriage and milk.
- al-Fatawa al-Hindiyya, Kitab al-Karahiyya, chapter on looking. What a woman may uncover in front of her mahrams.
This answer is pending review by the scholars on our team. Quran translation by Sahih International. Hadith Arabic from the standard editions of the six books and the Muwatta, with gradings as recorded there; the English is our own rendering. Spotted a mistake? Tell us.