The Gemara in Ketubot 72a outlines the issue of married woman covering her hair. This issue has been discussed already on this forum. Rav Yehuda Herzl-Henkin has wonderful and thorough treatment of the subject in Bnei Banim, also available in English here. Obviously the topic is very broad, I merely bring these points up as a preface to my question.The question being, it seems that much of the issues of uncovered hair are centered on Ervah, or at least on the notion of hair being meant to be covered. So if a woman doesn't have hair, it would seem that there is no need for her to cover her scalp. Is there any requirement for a bald woman to wear a kerchief on her head, or perhaps does having a bald head itself fulfill the requirement? (In the verse from which we learn the concept of hair-covering, it uses the word ראש/her head, rather than שער/her hair -- perhaps this is pertinent to the answer.) An adjunct to this question would be: if indeed a scalp-cover is not required, why do the many Chasidic women who shave their heads continue to wear a head cover? Is there a Halachic opinion that requires this, or is that a separate issue? Please bring any sources that support your answer.
Halachafortodaycom.blogspot.com says that there is two reasons why a married woman covers her hair. Although a bald woman may not have the problem of Erva, she still is required to cover her hair as a sign that she is married.
Q: If a married woman is bald, does she still have to wear a headcovering, or is she permitted to reveal her scalp? A: Besides for the reason that hair is considered “Erva” and must be covered, there is also a reason quoted by the Poskim that a married woman covers her hair as a “sign” that she is married, and this would apply to bald women as well. Also, even women that are bald are usually not 100% bald, and some hair is there.