Islam basically denounces excess in beautifying oneself to the extent of altering one’s physical features as Allah created them. The Glorious Qur’an considers such alterations as inspired by Satan, who “ …will command them (his devotees) to change what Allah has created…” (An-Nisa’: 119).

However, if undergoing such operation is just to address an unusual physical defect or alleviate embarrassment that makes one’s life miserable, this is something permissible under the rule of removing harm. This point is further clarified in the following fatwa issued by Sheikh Muhammad Iqbal Nadvi, Imam of Calgary Mosque, Alberta, Canada, and Former Professor at King Saud University, Riyad, Saudi Arabia:

“Shariah ruling for it can be different from one case to another. What I think of this kind of operation is that it can be done in both cases as follows:
1. A lady can resort to this kind of breast implant for the sole reason of seeking extreme and unnecessary beautification of the body in order to look, as she thinks, more sexually attractive. Actually this kind of beautification is unacceptable in Islam’s perspective. Islam is a religion of moderation and a woman should beautify herself with what Allah, the Almighty, has made lawful and never go to the extreme in this regard.
And I can find support for the prohibition of this extreme beautification in the following Hadith. It is reported in Al-Bukhari that a woman said to the Prophet, peace and blessings be upon him, “O Messenger of Allah, due to her being infected with measles, my daughter’s hair has fallen out, and I am about to give her in marriage. Shall I add some strands of hair to her hair?” Thereupon the Prophet, peace and blessings be upon him, replied, “Allah has cursed the Wasilah (a woman who makes wigs and hairpieces) and the Mustawsilah (a woman who wears wigs and hairpieces) (Reported by Al-Bukhari.)”
So, the Prophet, peace and blessings be upon him, did not approve of this kind of beautification though the woman was bald.
2. However, some women might resort to this operation of breast implant due to a considerable slimness or thinness in their breasts that it affects their relationship with their husbands and it might be a reason that their husbands will ignore them or become no longer interested in them. In this case, if we draw an analogy (Qiyas) between the aforementioned case where the Prophet, peace and blessings be upon him, forbade the lady to use wigs and pieces and this case of breast implant, we will find a difference between the two cases. In the first case, the lady is not married yet and this could be a trick to the new husband, something which is haram in Islam; however, in the other case the lady is already married and is seeking this kind of surgery to save her marriage. So, the Qiyas will be Qiyas ma’a al-fariq (analogy with discrepancy).
Thus, the case of woman resorting to breast implant for curing a remarkable slenderness would fall under the category of “Add-Darar yuzaal (harm should be prevented). So, it can be allowed as an exceptional case which should be judged according to the circumstances surrounding it.”