Today, many women grow their nails long and color them with nail polish. The question has been asked as to whether the nails must be cut and the polish removed before a woman immerses in a Mikveh. Halacha requires that the woman’s entire body come in direct contact with the water without any Hasisa (obstruction) in between. Do long nails and nail polish constitute "obstructions" in this regard, such that they must be removed before immersion, or do we consider them part of the woman’s body, and not an external obstruction?
The Ma’aseh Roke’ah cites the Rambam (Rabbi Moshe Maimonides, Spain-Egypt, 1135-1204) as discussing the question surrounding a type of paint that women used to wear on their hands for cosmetic purposes. The Rambam ruled (listen to audio recording for precise citation) that women are allowed to immerse with this paint on their hands because it has no "Mamashut" – substance. It is absorbed into the skin and changes its color, as opposed to forming a separate layer on top of the skin. Color does not constitute a Hasisa, the Rambam explains, and therefore this type of polish may be left on the hand during immersion. However, the Rambam noted that there was a different kind of paint which indeed had "Mamashut" and formed a layer over the skin, and thus would, in fact, constitute a Hasisa. This ruling also appears in the Rambam’s responsa (listen to audio recording for precise citation).
According to this position, nail polish would have to be removed before a woman immerses in a Mikveh. Nail polish forms a substantive layer on top of the nail, and is certainly not absorbed into the surface of the nail. Hence, it resembles the second kind of polish discussed by the Rambam, which the Rambam regards as a Hasisa with respect to immersion in a Mikveh.
However, the Rashba (Rav Shlomo Ben Aderet of Barcelona, 1235-1310), in his Torat Ha’bayit (listen to audio recording for precise citation), appears to take a different position. He writes that skin polish does not constitute a Hasisa because it is not something undesirable. A foreign substance is considered a Hasisa only when the woman generally ensures to remove it from her body, not wanting it on her skin. When it comes to polish, however, not only does the woman not ensure to remove it, she specifically wants it on her skin, and she was the one who put in there in the first place. The Rashba draws proof from the Parochet – the curtain in the Bet Ha’mikdash – which was dyed in various colors, and yet on occasion required immersion. Evidently, the dye did not constitute a Hasisa because it was wanted on the Parochet. The Rashba adds that he discussed this ruling with his mentor, the Ramban, who agreed with his analysis. This is also the view taken by Rav Menahem Meiri (Provence, 1249-1315; listen to audio recording for precise citation).
According to this view, it would be entirely permissible for a woman to immerse while wearing nail polish. Since she wants the polish on her nails, and does not want it removed, it does not qualify as a Hasisa, and thus does not have to be removed before immersion.
We will, please G-d, continue discussing this topic in the coming editions of Daily Halacha.