You might know an observant Jewish woman and never realize you're not seeing her real hair. Although it is not an explicit requirement in the Hebrew Bible, coverings for women is a common custom among Orthodox, or very observant Jews primarily because of modesty, piety and status.
Head covering is a tradition, rather than a law, notes jewishvirtuallibrary.org. Women who participate in relatively less observant streams of Judaism may only cover their head in a temple or synagogue. The most observant, Orthodox, women will almost always wear a head covering.
In a house of worship, temple or synagogue, women may cover their heads with something small, like a kerchief or piece of lace (tichal). Orthodox women may wear their hair in a snood, or cover their hair with a scarf or a wig (sheytel).
Modesty is the primary reason cited for head covering. There is an expectation for a woman to dress and appear modest; part of this is covering the natural beauty of her hair.
Many women who do not ordinarily cover their heads will do so during prayer. Judaism 101 mentions that in Eastern cultures it is a sign of respect to cover one's head; doing so during prayer shows respect for God.
In traditional Judaism, women are for the most part seen as separate but equal. Married women have an important role in maintaining the household and raising the family. A woman covering her hair after marriage is showing that she has a new, important status.
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