Gemara

(Mishnah): A woman may not go out with threads of wool or linen in her head, or ribbons;

She may not immerse with them unless she loosens them.

She may not go out with a needle without a hole;

If she went out with any of these, she is exempt.

Answer (Rav Nachman bar Yitzchak): This teaches that she may not go out with the threads because Chachamim require her to remove them before immersing, even during the week. If she will wear them on Shabbos, perhaps she will have to immerse, and she will remove them and carry them four Amos in Reshus ha'Rabim!

60a - Question: Why does a woman wear a needle without a hole [even during the week]?

Answer #1 (Rav Yosef): She is Ogeres her hair with it. (This will be explained.)

Objection (Abaye): If so, it should be like Biris (a garter belt to hold up socks), which is permitted!

Answer #2 (Rav Ada Narsha'ah): She uses it to part her hair.

Question: What does she use it for on Shabbos?

Answer (Rava): It has a gold plate at the other end. On a weekday she parts her hair with the needle. On Shabbos she wears the plate on her forehead.

94b (Mishnah - R. Eliezer): One is liable for braiding hair or Pokeses (fixing the hair with a comb or fingers; alternatively, applying a mudpack);

Chachamim forbid only mid'Rabanan.

(R. Avin citing R. Yosi b'Rebbi Chanina): R. Eliezer is Mechayev for braiding due to weaving, and for Pokeses due to spinning.

Objection (Rabanan): This is not the normal way to weave or spin!

(R. Avahu citing R. Yosi b'Rebbi Chanina): One is liable for braiding and Pokeses due to Binyan (building).

Objection (Rabanan): Is this the normal way to build?!

Answer: Yes!

(R. Shimon ben Menasiyah): "Va'Yiven Hash-m Elokim Es ha'Tzela" - Hash-m braided Chavah's hair and brought her to Adam;

Braiding is called 'Binyan' in the language of certain islands.

(Beraisa - R. Shimon ben Elazar): If a woman braided or colored her own hair or eyes or was Pokeses herself, she is exempt. If she did so for another woman, she is liable.

Nazir 42a (Mishnah): A Nazir may be Chofef (rub or shampoo) and be Mefasfes (this will be explained), but he may not comb his hair.

Question: The Reisha permits Chofef and Mefasfes. This is like R. Shimon, who permits Davar she'Eino Miskaven (something unintended that may result in a transgression);

The Seifa forbids combing. This is like Chachamim!

Answer (Rabah): The entire Mishnah is like R. Shimon. One who combs intends to uproot dangling strands.

(Mishnah - R. Yishmael): He may not shampoo with earth, because it causes hair to fall out.

Rishonim

Rambam (Hilchos Shabbos 9:19): If one aligns the threads and separates them at the time of weaving, this is a Toldah of weaving. Also braiding the threads is a Toldah of weaving.

Rambam (Hilchos Nezirus 5:14): A Nazir may not comb with a comb, for this definitely uproots hairs.

Rosh (6:1): Rashi explains that the threads are for braiding the hair. She must remove them before immersing. This is difficult, for even the opinion that exempts for braiding forbids mid'Rabanan. Presumably, just like one may not braid, one may not unbraid. Therefore, there is no need to decree, for one who wants to immerse must undo the braids before Shabbos. Rather, the threads are tight on her hair, and she must loosen them before immersing.

Rosh (7): A woman uses a needle without a hole to be Ogeres her hair. Rashi explains that this refers to hair outside the net. She wraps it around the needle, and sticks it inside the net, so her hair will not be seen. It seems to me that she inserts the needle in the cap and catches the cap on it, so her hair will not leave and be seen. This is like Biris. If she would remove it, her legs would not be exposed immediately, only after her socks fall. Rashi explains that the Gemara asked that one may not part hair on Shabbos. What is the source for this? It does not uproot hair! We permit even Chafifah and Mefasfes, like R. Shimon, who permits Davar she'Eino Miskaven. Also, even if it were permitted to part hair, the needle is a load! She cannot go out with everything she needs, since it is not a garment or Tachshit (ornament). Rather, the Gemara asked why she may go out with it on Shabbos, for it is not a Tachshit. It answered that the needle has a gold plate at the other end. On a weekday she parts her hair with it. It is forbidden on Shabbos, lest one remove it to show it off [and come to carry it]. She may go out with a needle to support her net. This is like a needle to be Ogeres her hair [which we permit].

Poskim

Shulchan Aruch (OC 303:26): One may not braid her hair on Shabbos, nor unbraid it, but she may part her hair.

Beis Yosef (DH u'Mah she'Chasav v'Lo): The Kolbo says that nowadays the custom is to braid hair [on Shabbos], and no one protests, for it is better that Yisraelim transgress b'Shogeg [than b'Mezid]. We cannot stop them, lest they become repulsive to their husbands.

Bedek ha'Bayis (DH: This is unreasonable. The hair is covered. How will she become repulsive?! We never heard of such a custom. If such a place is found, they should be rebuked.

Magen Avraham (20): Braiding is like Binyan. One who braids detached strings is liable for weaving, like the Rambam says. Regarding hair, it is not considered weaving. Also, it will not last, for it is destined to be undone. Tal Oros erred about this.

Kaf ha'Chayim (117): This is like the Rambam, who rules like Chachamim. According to those who rule like R. Eliezer, one is liable for braiding.

Magen Avraham (21): She may part because she does not intend to uproot hair.

Mishnah Berurah (82): It is forbidden mid'Rabanan because it resembles Binyan, like we expound "va'Yiven Es ha'Tzela". One is not liable for weaving, since it is attached. Binyan does not apply to braiding a wig, but weaving applies. Even if it will not be permanent, it is forbidden mid'Rabanan. One should not protest in a place where people will not listen.

Mishnah Berurah (83): Unbraiding resembles destroying.

Shulchan Aruch (ibid.): Some forbid parting her hair. The custom is to forbid through a Kli, but to permit through one's finger.

Mishnah Berurah (84): Some forbid parting, lest one uproot hair. The first opinion permits because she does not intend, and it is not a Pesik Reishei.

Kaf ha'Chayim (118): One may delouse a hide where there is no wool, but not where there is wool, and not on the head, lest he uproot hairs.

Shulchan Aruch (27): One may do Chafifah and Mefasfes by hand.

Beis Yosef (DH u'Mashma): They (Tosfos and the Rosh) connote that it is permitted only to part the hair. Since she does not uproot hair, even Chafifah and Mefasfes are permitted, for we hold like R. Shimon, who permits Davar she'Eino Miskaven. Rashi in Shabbos (94b) says that fixing hair with a comb is Asur due to Binyan. He did not say due to shearing for it is a Pesik Reishei! There, it does not mean combing, rather, braiding. Or, it is passing a comb wet with oil and water on a combed head to make the hairs stick together.

Kaf ha'Chayim (122): Also Chidushei ha'Ran (94b) says so in the name of the Ro'oh. However, Tosfos (42a DH Aval) says that this depends on the argument [of Eliezer and Chachamim].

Magen Avraham (23): Rashi (50b DH Chofef) says that Mefasfes is Menafetz (spreading out). Tosfos and Rashi in Nazir say that Mefasfes is separating hairs from each other. The Rivash connotes that passing a wet comb on a combed head is forbidden only due to Binyan.

Mishnah Berurah (88): Mefasfes is separating the hairs by hand. The Rambam says that he is Chofef by hand and scratches with his nails. Even if hair falls, he is not concerned, for he did not intend for this, and it is not certain to occur.

Kaf ha'Chayim (127): Hair of the beard falls out easily, and the hands fidget, so one should not touch his beard on Shabbos. The Ari Zal warned to be careful even during the week not to uproot even one hair.