Everyone who intends to offer a sacrifice has to refrain from clipping nails and cutting hair after beginning the first ten days of Dhul-Hijjah. It is forbidden for such a person to cut his hair or nails. The majority of the Muslim scholars believe that it is merely detestable for the Hadith narrated by Umm Salamah (Radiya Allahu Anha) that the Prophet (Sallallahu Alaihi wa Sallam) said: "When the first ten days of Dhul-Hijjah starts, one who intends to offer a sacrifice should not have his hair cut or his nails trimmed, till he/she has offered his/her sacrifice". [Reported by Imam Muslim]
It is reported in a narration that he should not remove any of his skin.
The wisdom behind the above ruling is for all the parts of body to remain freed from the Hell.
If one cuts his/her hair or nails he/she has to ask forgiveness of Allah only and has to pay no expiation.

http://www.islamweb.net/emainpage/index.php?page=showfatwa&Option=FatwaId&Id=83881