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For mikveh immersion to be kosher, there must be no barrier (ĥatzitza) separating the woman from the water. What is considered a barrier for these purposes? Whatever most women would not want stuck to their body or hair, such as lice or nits, dirt, and knots in hair. To get rid of knots, the hair must be shampooed and combed out well. Hair dye which still looks good does not need to be removed. If peeling skin, scabs, and calluses can be easily removed by soaking them in water, (and this will not cause bleeding), they should be removed. If it is difficult, they do not need to be removed. Creams which are absorbed by the skin are not a problem even if their effects can be felt on the skin.
A woman is not required to open her mouth during immersion, but it is permissible for her to do so. Therefore, there must not be any barrier there, such as a shred of meat caught between the teeth. A properly made filling, even a temporary one, is not a problem. However, if a woman is embarrassed to be seen with the temporary filling, it is a barrier.
Anything on the body that is tightly fitted should be removed so that the entire body can come into contact with the water. This includes rings, earrings, hair pins, necklaces, and bracelets. Anything stuck to the eyes or eyelashes, such as leftover makeup, should be removed. Many women cut their nails before immersing, as dirt can get underneath. If a woman likes to have long nails, she can immerse as long as she cleans beneath them very well. If she wants to immerse with her nails polished, she must make sure they look good and are unchipped. Finally, she should blow her nose.
All these preparations should be done calmly. Some women prepare in preparation rooms at the mikveh, while others do so at home.
