Muslim women cover their hair because Koran advises that a woman should cover her head past the neck opening of their dresses or tops so as to not display her "ornaments" to males outside her family. "Ornaments" is interpreted, by Islamic scholars, to mean "hair."
The typical head covering of a Muslim woman is the hijab, a scarf or hood that covers everything down to the shoulders but the face. This, Islamic teaching indicates, expresses modesty and helps eliminate unwanted attention from others in the form of envy, admiration, flattery or sexual attraction. Women and men are advised to dress modestly in other ways, specifically by covering most of the body other than the hands. While dress is important, respectful and modest conduct is critical to proper modesty and respect for Islamic teachings as well.
Besides the hijab, Muslim women may wear more extreme head coverings that include the face. The niqab, for example, includes a veil that sometimes leaves nothing exposed but the eyes, and the burqa even covers the eyes with a screen. Despite the original intent of modesty, these Muslim head coverings have become increasingly politicized, with some countries banning the niqab or even hijab in public buildings. Further, some Muslim women are wearing these coverings as a political statement, while Muslim feminists like Ayaan Hirsi Ali speak out against any prescribed head coverings at all, viewing even their voluntary wearing as a subjugation of women.