Must a married [or once married] woman cover her sideburns and others hair that protrude past the regular hair of the head?
Some Poskim rule a married women is not required to cover her sideburns or any other hair that protrudes past the head, such as by the back of the neck and behind the hair. Other Poskim however rule it is required to be covered just as any other hair of the head. Nevertheless she may uncover the sideburn areas when privately with her husband even at times that she is a Nida.
 Admur 75/4 “So too the hairs of women which regularly protrude from their regular hairline in some lands, is permitted to be revealed in front of those learning Torah and Davening, as since the people are accustomed to see this area of hair revealed it therefore does not lead to erotic thoughts.”; Rama 75/2; Raavad brought in Rashba
 Some write the rule is that all hair that does not grow long is considered as the “Tzamsan” which is not required to be covered.
 Tzemach Tzedek Even Haezer 139/2; Chasam Sofer 36; These Poskim learn that the ruling of the Poskim above [Rama and Admur] were only said regarding a wife and husband and not regarding other people.
 Tzemach Tzedek ibid; Chasam Sofer ibid; Shalmas Chaim 64