The Qur'an itself states that only those who are clean and pure should touch the sacred text: "This is indeed a Holy Qur'an, in a book well-guarded, which none shall touch but those who are clean..." (56:77-79). The Arabic word translated here as "clean" is mutahiroon, a word that is also sometimes translated as "purified".
Some argue that this purity or cleanliness is of the heart, i.e. that only Muslim believers should handle the Qur'an. However, the majority of Islamic scholars interpret these verses to also refer to a physical cleanliness or purity, which is attained by making formal ablutions (wudu). Therefore, most Muslims believe that only those who are physically clean through formal ablutions should touch the pages of the Qur'an.
As a result of this general understanding, the following "rules" are usually followed when handling the Qur'an:
1) One should make formal ablutions before handling the Qur'an or reading from its text.
2) One who is in need of a formal bath (after intercourse or menstrual bleeding) should not touch the Qur'an until after bathing.
3) A non-Muslim should not handle the sacred text, but may listen to tapes of the Qur'an or handle a translation or exegesis.
4) Those who are unable to handle the Qur'an based on these reasons should either avoid handling the Qur'an completely, or in necessity hold it while using some sort of barrier covering the hand, such as a cloth or a glove.
In addition, when one is not reading or reciting from the Qur'an, it should be closed and stored a clean, respectable place. Nothing should be placed on top of it, nor should it ever be placed on the floor or in a bathroom. To further show respect for the sacred text, those who are writing it should use clear, elegant handwriting, and those who are reading from it should use clear, beautiful voices.
In summary, Muslims believe that the Holy Qur’an should be handled with the deepest respect. However, God is All-Merciful and we cannot be held responsible for what we do in ignorance or by mistake. The Qur'an itself says: "Our Lord! Punish us not if we forget or fall into error" (2:286). Therefore, there is no sin in Islam on the person who mishandles the Qur'an by accident or without the realization of wrongdoing.