For religious reasons

Head-shaving is a part of some Buddhist, Christian, Muslim, Jain, Jewish and Hindu traditions. Buddhist and Christian monks generally undergo some form of head-shaving during their ordination; in Thailand monks shave their eyebrows as well. Brahmin children have their heads ritualistically shaved before beginning school.

In some parts of the Theravada Buddhist world, it is common practice to shave the heads of children. Weak or sickly children are often left with a small topknot of hair, to gauge their health and mark them for special treatment. When health improves, the lock is cut off.

In Judaism, men are prohibited to shave the beard and sideburns using a blade against the skin. However, electric razors may be used, since the cutting blade does not directly touch the skin. Women are allowed to shave their heads; in some Hasidic circles, married women traditionally shave their heads since they are prohibited to expose their hair to men other than their husbands and families.

The Bahá'í religion explicitly prohibits head-shaving. Sikhs take an even stronger stance, opposing all forms of hair removal. One of the Sikh "Five Ks" is Kesh, meaning "uncut hair". To Sikhs, the maintenance and management of long hair is a manifestation of one's piety.

Muslim law (Sharia) puts hair in three categories: that which it is recommended to remove (pubic and armpit hair), that which it is recommended to keep (the beard), and that which is the object of limited recommendation (foot, hand, back, and chest hair). Removal of armpit and pubic hair is a hygienic practice which was taught by Muhammad and which was enumerated as having been part of practices conforming to man's premortal (Fitrah) nature. On the other hand, shaving or removing part of the eyebrows is forbidden as the "modification of the creation of Allah and obedience to Satan in his work to fool men and bring them to modify the creation of Allah." Stray hairs between the eyebrows may be removed, but not the hairs of the eyebrows. A male may trim or cut hair on his head—however shaving of the head is forbidden in some branches of the religion. A male may trim hair on the chest and back but may not remove it, as this is considered to be too feminine. In contrast, women are permitted to remove hair from these areas.[5] In the 9th century, the use of chemical depilatories for women was introduced by Ziryab in Al-Andalus.[6]

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