Must a woman observe hijab in front of her relative who has Down syndrome, who does not comprehend religious matters, nor distinguish between unmarriageable female kin (maharem), nor know anything about matters of marriage, knowing that doctors have confirmed his lack of sexual desire?

A woman must cover her entire body from non-mahram men, except for "men who lack sexual desire" (ghayr uli al-irbah min ar-rijal). These are men who do not comprehend women's matters, are not inclined towards them, and have no sexual desire. It is permissible to uncover before them what is typically visible, such as the head, face, arms, and feet.

However, for anyone who understands women's matters and has an inclination towards them, or exhibits desire upon seeing them, it is not permissible to uncover before him. This includes those who have lost their sexual desire due to old age or an incurable illness, or a hermaphrodite who lacks sexual desire.

But if the hermaphrodite has sexual desire and understands women's matters, his ruling is the same as others, based on the hadith of the hermaphrodite who described a woman to the Prophet, peace and blessings be upon him, after which the Prophet ordered him to be veiled from women.

Similarly, concerning a mentally handicapped person: if their disability is severe and they do not comprehend or understand women's matters, and have no sexual desire, there is no need for hijab from them. However, if they understand some of these matters and have an inclination towards women, then it is not permissible for them to enter upon women.

Therefore, the relative's attentiveness to the beautiful woman and his keeping of women's pictures indicates that he is not entirely lacking in sexual desire, and thus it is not permissible to uncover before him.