Showering after Mikveh:
For how long of a period after immersing in a Mikveh is a woman to avoid bathing?
Some Poskim rule she is to avoid bathing for that entire weekday, [until after sunset]. Other Poskim rule she is only to avoid bathing until the morning. The above applies whether or not marital relations have taken place, and either way she is [only] permitted by the next day. Other Poskim rule she may resume bathing as soon as she returns home from the Mikveh. According to all opinions, once the day of immersion has passed she may resume bathing as usual. This applies even if marital relations have not yet taken place, as stated above.
How much of the body is forbidden to be bathed according to the above custom?
The prohibition applies against simultaneously bathing the head and majority of the body. It is permitted according to all to bathe minority of the body after Mikveh.
May a woman take a shower after Mikveh?
No. The above accustomed prohibition includes all forms of bathing, whether a bath or shower. However in a time of need she may shower her body in segments, such as to first place only her head under the water and then shower only her body, excluding the head, or vice versa. [Alternatively she can even shower her entire body if she uses less than three Lugin of water from the shower. Some suggest that she can place a shower cover over her head and then shower regularly.]
What is the law if a woman transgressed and bathed her body after Mikveh, must she re-immerse?
No. Her immersion remains valid even in such a case.
If a Kallah went to Mikveh before her wedding, until when is she to avoid bathing and showering?
According to all she may bathe and shower regularly starting from the next weekday after she immersed. Thus if she immersed on Monday night she can bathe/shower starting Tuesday night. Some Poskim even allow her to bathe/shower beginning from Tuesday morning, and some even allow her to bathe/shower on Monday night upon arriving back home.
If a Kallah went to Mikveh on the day of her wedding, may she shower at night after the wedding?
Yes, she may shower regularly. However she is not to shower regularly prior to sunset.
May a man take a shower after Mikveh?
It is permitted for men to shower after Mikveh, although some are stringent not to do so. Nevertheless, on Erev Shabbos [and Erev Yom Tov] according to all it is better not to do so, in order so one not completely wash off the Mikveh water from his body, as will be explained next.
 Rama 201/75; Ridbaz 4/205; Taharah Kehalacha 22/29-30 [pp. 565-567]
Other opinions: Some Poskim rule it is permitted for a woman to bathe her entire body after Mikveh as the above decree was only made against immersing for purity to eat Teruma, and not for the purity of a woman to her husband. [Rav Yeshaya Matrani brought in Or Zarua ibid; Gr”a 201/75; Poskim brought in Ridbaz 4/205; Peri Hadama and Rabbeinu Yeshayah 152, brought in Birkeiy Yosef 201/75 in Shiyurei Bracha, and Darkei Teshuvah 201/332] The Igros Moshe 2/96 concludes that in a time of need, such as by a very pamppered women, she may be lenient like these opinions.
 Mordechai in name of Rashbam; Or Zarua Nida 338; based on Shabbos 14a
 The reason: In order so people do not come to say that it is the bath which she does after the Mikveh has the same power of purification as the Mikveh, and this could lead to people skipping immersion in the Mikveh altogether and simply take a bath. [Shach 201/151]
 Or Zarua ibid writes “that day” which seemingly means for the entire weekday of that day; Rashi Shabbos 13b; Igros Moshe Y.D. 2/96, Taharah Kehalacha ibid
 See Igros Moshe ibid
 Thus if she went to Mikveh on Monday night, she is to avoid bathing until Tuesday night.
 See Taharah Kehalacha ibid
 Thus if she went to Mikveh on Monday night she may bathe starting Monday morning.
 Igros Mose ibid; Thus she may not bathe until the next day even if she already had marital relations, and on the other hand she may bathe regularly once the next day has arrived even if she did not yet have marital relations. Those that avoid showering until after marital relations, even if many days have passed, are mistaken, and their custom is baseless and is to be changed. [Igros Moshe ibid]
 Shevet Halevi 5/125; Rav SZ”A brought in Taharah Kehalacha ibid; See Igros Moshe ibid that from the Rama ibid it is implied the prohibition only applies immediately after immersion, although perhaps one can also interpret it to mean until the next weekday
The reason: As no one will come to think that the bath taken in her home is for purification. [ibid]
 Or Zarua ibid; Igros Moshe ibid
The reason: As otherwise there is no limit to this matter, and she will be forbidden to bathe forever [or only when she is impure]. [ibid]
 Taharah Kehalacha ibid
 Such as a Kallah whose seventh day fell on the day of her Chupah.
 Taharah Kehalacha ibid based on Gemara Shabbos ibid
 Igros Moshe ibid; Taharah Kehalacha 22/29 [p. 565]
 See Or Zarua ibid that the prohibition is only against bathing and pouring three lugin of water on her body. Accordingly it would be permitted according to all for her to enter the shower for a short amount of time, less than three lugin.
 See Beir Moshe 6/140
 Avi Ezri brought in Or Zarua ibid; Ridbaz 4/205; Igros Moshe Y.D. 2/96; Taharah Kehalacha ibid
Other Poskim: According to the Mordechai ibid she becomes impure to her husband if she bathes after Mikveh and hence she is required to re-immerse. [See Igros Moshe ibid]
 The reason: As there are many Poskim that even initially permit doing bathing and hence it suffices to be initially stringent. [ibid]
 See first Q&A above!
 Such as when her 7th day of count fell on the day of her Chupa,
 As according to all one may shower the next weekday even prior to marital relations, and hence if she immersed Monday afternoon, she may shower Monday night.
 Sheivet Halevy 7/33; Piskeiy Teshuvos 88/8; Even regarding a Nidda the Rama Yoreh Deah 201/75 rules that only some opinions are stringent and so is the custom. However others argue on Rama and rule doing so is permitted even by a Nidda. [See Gr”a ibid; Darkei Teshuvah 202/332; Lechem Vesimla 122]
 Piskeiy Teshuvos 260/1 in name of Sheivet Halevy that so is the custom of the world to avoid doing so despite it being allowed from the letter of the law. See also Tiferes Adam 1/28 which rules one should never shower after Mikveh.