It goes without saying that physical deformation, which may affect the relation between two spouses, must be disclosed before marriage. Yet, simple defects that may not affect the relation between the spouses, neither physically nor psychologically, need not be disclosed, though sometimes keeping the other party informed about them will be better, in order not to leave a room for suspicions.
Dr. Abdul Fattah `Ashoor, professor of the Exegesis of the Qur’an at Al-Azhar University, states the following: “Asma’ bint Abu Bakr, may Allah be pleased with her, reported that a woman asked the Prophet, peace and blessings be upon him: ‘O Allah’s Messenger! My daughter was infected with measles that caused her hair to fall. Now that I’m giving her in marriage, can I adjust her hair with artificial braids?’ Hence, the Prophet, peace and blessings be upon him, replied: “Allah has cursed the lady who adds artificial hair (to hers or to someone else’s) (Al-Wasilah) and also the one who asks for it (Al-Mustawsilah).”
This Hadith is taken as a hard evidence on the necessity of telling the suitor about any defects, because he may not be satisfied with a lady with a fallen hair, and hiding such defects amount to an act of deception. But if he is informed of the issue before marriage, he will have the option either to go ahead with that or not.
So, if a birthmark in the leg for example is the kind of defect that is likely to affects the relation between the parties to the marriage contract, then it must be revealed. But if it is a simple thing that does not deface the leg, there is nothing wrong that. May Allah guide you to the Straight Path!”
Shedding more light on the issue, Dr. `Abdul Fattah Idrees, professor of Comparative Jurisprudence at Al-Azhar University, adds: “If a lady suffers from any disease, she has to inform her suitor of it, because on knowing about her disease the suitor may refrain from marrying her. So the Prophet, peace and blessings be upon him, urged frankness between a lady and her suitor. It is reported that Al-Mughirah ibn Shu`bah, may Allah be pleased with him, proposed to a woman from Al-Ansar (the Helpers). The Prophet, peace and blessings be upon him, asked if he had seen her. The man told him that he hadn’t. Hence the Prophet, peace and blessings be upon him, said to him: “Go and see her, because Al-Ansar have some defect in their eyes.” Some scholars refer to this defect as weak-sightedness.
Therefore, a suitor should be informed of any diseases, whether hereditary or not, infecting the lady he is proposing to. The other way round, a lady should also be informed of the same things in her suitor. This is to evade the bad consequences of knowing this after marriage, for this may cause nullification of marriages contract.”