Chafifah on Yom Tov
A woman whose immersion falls on the second night of Yom Tov, Friday night following a Yom Tov, or Yom Tov following Shabbat needs to prepare on the last available weekday - even if this is several days before her immersion. On Shabbat or Yom Tov, she should try to avoid acquiring new chatzitzot; however, eating meat is permissible. Immediately before immersion, she should clean her teeth, separate strands of hair with her fingers, wash any parts of her body that may have become dirty, and visually inspect herself for chatzitzot. (Inspection should be done at the mikveh itself.) The procedure for immersion is the same as on a regular Friday night.
Some aspects of preparation can be refreshed on Yom Tov itself, as long as the following guidelines are observed:
It is prohibited to prepare on Shabbat or Yom Tov for the following day. Therefore, one may not prepare on Shabbat for Yom Tov, or on the first day of Yom Tov for the second day. But when Yom Tov falls on Friday, one may prepare for Shabbat because of the eruv tavshilin.
Heating up water is a form of cooking, which is prohibited on Shabbat and permitted on Yom Tov. Opening the hot water tap generally causes cold water to enter the heating tank and become cooked. Therefore, hot water from the tap may be used on Yom Tov, but (with most systems) not on Shabbat.
In order to ensure that water is not heated on Shabbat, there is a rabbinic decree against washing the entire body with heated water (even if heated before Shabbat). Therefore, one may wash one part of the body at a time with hot water. There are different opinions about bathing or showering with hot water, and a specific question should be asked. It is permitted for a woman to immerse in a heated mikveh on Shabbat if her husband is in town, in order to fulfill the mitzvot of peru urevu (procreation) and onah (marital relations).
To avoid the prohibition of m'machek (smoothing), liquid soap should be used rather than bar soap. To avoid the prohibition of s'chitah (wringing out), one should not use a washcloth or wring out a wet towel. A woman should pat her hair gently with a towel when she comes out of the mikveh rather than wringing out the water.
There are different halachic opinions about cleaning teeth. One should not use regular or gel toothpaste. Most authorities permit using a toothbrush with water or with liquid toothpaste. Toothpicks or pre-cut dental floss may be used, unless a woman is certain that they will cause her gums to bleed.
One may not comb hair or brush it with a regular brush (to avoid problems of gozez - removing hairs). Hair also may not be braided or unbraided (this is considered boneh - building). The best strategy is to comb the hair well during preparation, tie it back so it won't become too tangled, and gently run one's fingers through it to separate the strands just before immersion.
One may not cut hair or nails or remove hanging skin on Shabbat or Yom Tov, as gozez applies to removing anything growing from the body.