I am usually very thorough preparing for the mikvah. Last night however, I forgot to clean my navel. I usually do it to prepare for the mikvah, but never at other times because it doesn't usually accumulate anything. However, after I immersed last night, I noticed a sign on the wall saying to clean your navel. I looked hard and there was the tiniest bit of something that was very difficult, and slightly painful, to remove. In hindsight, I should have asked the mikvah lady what to do, but I didn't feel so comfortable calling her and just left. Was this considered a Chatziza? What do I do now?
Answer
Based on what you write, your immersion remains valid. No further steps are necessary.
The navel should be inspected and cleaned prior to immersion. However, this does not require removing tiny flaps of skin or intensive cleaning. It is more a precaution to remove any piece of foreign matter or secretion no longer attached that may have found its way into the area.
