Chatzitzot (Barriers to immersion)
(1) it covers the majority of her body;
(2) she minds its presence – that is, it is a substance that she considers foreign and plans ultimately to remove.
The rabbis decreed, however, that a substance meeting only one of these conditions (either it covers the majority of her body or she minds its presence) also invalidates the immersion.
Thus, in practice, a barrier of any size is considered a chatzitzah if it is destined to be removed. Even when the woman does not mind the barrier's presence while she is immersing, if she would normally remove it at some other time (e.g., a ring that she removes only when kneading dough) it is a chatzitzah. Furthermore, if most women would be particular about an item, then it is considered a chatzitzah even for an individual who does not mind its presence.
Every attempt should therefore be made to remove even minute amounts of foreign material before immersing. If, however, a barrier is inconvenient, difficult or impossible to remove, then a rabbi should be asked whether the item is actually a chatzitzah. Some examples are:
1. The foreign material has a medical role (e. g., stitches).
2. Its removal would be dangerous.
3. It serves a cosmetic purpose (e. g., hair color).
4. It is permanently attached to her body.
In such situations consultation is essential. A woman should never assume on her own that foreign material is inconsequential, and risk an invalid immersion, but neither should she take it for granted that it is indeed a chatzitzah, and perhaps needlessly delay immersing in the mikveh.