This is a complex question.
For something to be considered a chatzitzah, barrier to immersion, on even a rabbinic level, it needs either to cover most of the body’s surface or to be something that women are particular to remove. For hundreds of years, widespread practice has followed the view of Rema to remove everything possible prior to immersion, even when an item is small and women are not particular about it. This includes strong customs to trim and thoroughly clean the nails, though there is often some extra halachic leeway regarding toenails, about which women are usually less particular. Therefore, preferred practice is to remove all nail polish prior to immersion.
On the other hand, early halachic authorities argue that dye such as henna on the body is not a chatzitzah, for two reasons: it is in place for beautification and it does not have an independent physical substance. It’s not clear whether a potential barrier needs to share both of these properties, or whether one is sufficient. One could argue that nail polish has its own independent substance, but its being there for the purpose of beautification might still suffice to allow for immersion with polish so long as it is fully intact (as after a fresh manicure).
For this reason, a woman who would prefer to skip or postpone immersion rather than remove her nail polish is typically allowed to immerse with a well-maintained manicure after cleaning her nails well.
In your case, if your custom has been to remove polish prior to immersion, it would be best to keep to that. There could be room for extra leeway with a pedicure, perhaps scheduling a manicure at your destination. If it is very important to you, however, there are grounds to immerse with the manicure as well. Should you choose to do so, please be aware that mikveh policies differ, so you may need to explain this ruling in advance to the attendant. Learn more about the halachot of nails and mikveh here.
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This response was updated on 15 January, 2024.