Tosafos discusses the prohibition of cutting of pei'os ha'rosh. It is clear from the gemara in makos that for pei'os ha'zakan one is only in violation if they use a razor (or perhaps something that cuts as close as a razor - discussed in a previous blog). Although this stipulation isn't mentioned in regard to pei'os ha'rosh, it is possible that it has the same limitation and that one is only in violation if they cut their pei'os with a razor. Tosafos struggles with this issue and tries to prove that the the issur of pei'os ha'rosh applies even with a scissors (if it is cut to a point that the hair can't be bent back to its root). In Shluchan Aruch (181:2) he cites the opinion that even pei'os ha'rosh requires a razor (and considers this to be the primary opinion), then quotes Tosafos that even with scissors it is assur, and concludes - ויש לחוש לדבריהם.
R. Akiva Eiger (Gilyon HaShas) raises a very interesting point. Based on the opinion of Tosafos that there is a prohibition to even use a scissors, it should follow that even pulling out the hair with a tweezers (מלקט ורהיטני) should be assur - since we expand the issur beyond a razor, we have no source to limit it to scissors and not tweezers. Therefore, even combing one's hair which will pull out hairs should be assur. R. Akiva Eiger explains that this would not qualify as a דבר שאינו מתכוין which is mutar, because the in the context of Nazir we consider combing hair to be a p'sik reisha since it will inevitably pull out hair. How then can one comb their hair?
R. Akiva Eiger in a Teshuva rejects the notion that we can rely on s'feik s'feika, maybe the halacha is like the opinion that forbids only a razor, maybe the halacha is like the opinion that the entire area has to be rounded off to be in violation (rambam holds it is only forbidden if there are less than 40 hairs that remain - chasam sofer understands that 2 remaining hairs are sufficient m'doraysa, but 40 are needed m'drabonon). Using this s'feik s'feika, it should be permitted to cut with a scissors, yet the shulchan aruch is machmir and forbids cutting the area even with a scissors implying that we assume like the s'mag that even cutting 2 hairs in the area of the pei'os would be a violation. How then can one comb their hair?
The Chasam Sofer (Y.D. 139, 140) responds to R. Akiva Eiger's question. One of the points that the Chasam Sofer (140) raises is that even if tweezers is forbidden, combing should be permitted. The concern that combing will pull out hair (which is found by Nazir) is by loose hairs that are already partially out. In the context of Nazir that would be a violation, but it would not constitute a violation of cutting off pei'os. The Chasam Sofer (139) defends the practice of combing hair because he saw his Rebbi R. Nosson Adler do it. The Chasam Sofer develops the same s'fek s'feika that R. Akiva Eiger (teshuva 63 k'sav yad) raises. The fact that the Shulchan Aruch doesn't consider it to be a s'fek s'feika, the chasam sofer (140) considers to be a question on the Beis Yosef, "let someone with a broader mind than us answer up the beis yosef".