Question: Can you please tell me why married women have to wear a wig?
Answer: Thank you very much for your question. Although there is no obligation for a woman to wear a wig, there is a Torah prohibition for a married woman to appear in public with her hair uncovered. Jewish, obligatory custom (Daas Yehudis) restricts a married woman from appearing in front of men other than her husband, or in semi-public places (e.g. her front yard) with her hair uncovered.
There are various customs regarding when a woman should start covering her hair. In some communities, the woman covers her hair before the wedding ceremony. In others, she covers her hair after yichud (when, following the wedding ceremony and prior to the wedding feast, she and her husband are secluded). Still others wait until the morning after the wedding, once she and her husband have had relations.
However, she may choose to cover her hair in any way she wishes. Although many women in our generation choose to do so with a wig, there is no such obligation any more than to use a kerchief. As a matter of fact, there is a minority opinion (most notably among Sefardi and some Chassidic Jews) that feel that a wig does not qualify as a head covering!
Although this obligation is not stated explicitly in the Torah, it has been handed down to us from Sinai (Halacha L’Moshe MiSinai) along with many other laws, and is as binding as any Torah obligation. However, the Talmud in Kesuvos (72a-b) tells us that this obligation is alluded to in the Torah in the section discussing a Sotah (Numbers 5:18).
Rabbi Aaron Tendler
[For another view on hair covering for married women, please see here.]