Nida 67b - Chatzitza D'oraysa

The gemara says that to qualify as a chatzitza d'oraysa it must be both רובו ומקפיד, meaning it must cover the majority of one's body and one must be makpid in not wanting it there. The Rabbonon are go'zer to consider it a chatzitza even if it is רובו or מקפיד. If it is neither רובו or מקפיד it is not even chatzitza d'rabonon (just a minhag to remove everything prior to going to the mikva). 

Rashi interprets the entire gemara to be referring to a chatzitza on the hair, presumably because it immediately follows a gemara that talks about knots in the hair being a chatzitza. Both Tosafos HaRosh and Tosafos in Succah 6a understand from Rashi that it is only in the hair where we consider something to be a chatzitza d'oraysa ONLY if it is רובו ומקפיד, but on the rest of the body it would be regarded as a chatzitza d'oraysa even if it is a מיעוט שאינו מקפיד. 

Perhaps this is the source of the Rama (beginning of 198) who requires a woman to remove everything prior to going to the mikva, because according to the Tosafos and Tosafos HaRosh understanding of Rashi, everything is a chatzitza on the body. It is difficult to understand why the Tosafos and Tosafos HaRosh learn Rashi to be holding that even a מיעוט שאינו מקפיד is a chatzitza on the body, rather than saying that what is only d'rabonon by the hair such as מיעוט המקפיד or רובו שאינו מקפיד is a chatzitza d'oraysa on the body. 

Tosafos disagrees with Rashi and understands the gemara to be speaking about the body, not the hair. 

Perhaps even Rashi would hold that the same halacha that we find by the hair (according to his understanding that the gemara is talking about the hair) would apply to the body as well. The reason Rashi would limit the gemara to be speaking about hair could be because he holds like the opinion cited by the Rambam that we view hair as an independent entity. Meaning, the halacha of רובו is the majority of the hair, or the majority of the body. Rashi could simply be saying that if the majority of the woman's hair is tangled, each hair onto itself, it would be a chatzitza d'oraysa because it would qualify as רובו ומקפיד even though there is no chatzitza on the body. The same would be true on the body if there was a chatzitza covering the majority of her body, even if there were no chatzitza on her hair.