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12. Perspiring on Shabbos in a bathhouse:
Entering a steam room: The Sages forbade one to enter a bathhouse even in order to merely perspire [one’s body].
The reason for this is: due to the transgressors who would bathe themselves in hot water and claim that they were just perspiring.
To pass by a steam room: [Furthermore] there are opinions which say that even to walk past a bathhouse by an area where one is able to perspire is forbidden even though he has no intention to perspire.
|Summary- Perspiring on Shabbos in a bathhouse:
Is forbidden. Some even forbid walking by an area that will cause one to perspire even if he has no intention to do so.
May one enter a Mikveh in which he knows that its heat will cause him to perspire?
No. Thus, if due to the heat of the Mikveh room one will perspire upon staying there for a long time, he must dress quick enough after leaving the Mikveh water to prevent perspiration. Nonetheless, women who go to Mikveh on Friday night may be lenient in this matter if necessary.
May one enter a bathhouse in which he will sweat if he is wearing his clothing?
Some Poskim rule it is permitted to do so.
May one enter an area in order to sweat if it is not a bathhouse?
May one use a Sauna on Shabbos?
If the sauna is in a bathing area, then it is certainly forbidden to use it. If, however, it is not in a bathing area then this matter requires further analysis. Practically, one is not to enter a sauna on Shabbos, even a dry sauna.
May one take a suntan on Shabbos?
Doing so does not contain a sweating prohibition being that the sweating prohibition is only relevant when it is caused by hot water, as in that case the Sages feared that one may bathe and merely claim that he is sweating. However, if there is no water involved then mere sweating is permitted, as Admur ruled earlier regarding sweating in the Tiberius springs which is allowed. Nevertheless there are other possible prohibitions involved in sun tanning and practically it is disputed amongst Poskim if it is allowed. See the next section “The Laws of Smearing Oil”!
May one leave a humidifier on in his room throughout Shabbos in order to sweat?
Yes, as stated in the previous Q&A!
May one wear many layers of clothing in order to sweat?
 Admur 326:12; 616:1 in parentheses; Michaber 326:12; Shabbos 40a
 Admur ibid; M”B 326:35; Gemara ibid
 Rama 326:12; Rashi Shabbos ibid; Rosh 3:7; Ran ibid; Tur
Other opinions: According to the first opinion mentioned above [of Michaber ibid] it is permitted to do so. [M”B 326:35 in name of Beis Yosef]
 This means that one will for certain perspire, as if it is not a Pesik Resihsei, then it is permitted if one has no intent to do so. [Olas Shabbos 326:23; Kaf Hachaim 326:54]
 Admur 326:12
 M”B 326:36; Ketzos Hashulchan 133 footnote 13
 Ashel Avraham Butchach 326; Piskeiy Teshuvos 326:16
 Ashel Avraham Butchach 326; Piskeiy Teshuvos 326:16 based on Admur 326:2 and M”B 326:11
 The reason: As the prohibition is only applicable in an area that contains water in which it is forbidden to bathe, as rules Admur 326:2 regarding the Tiveria springs, and perhaps in this case the stringent opinion would also be lenient.
 As in the previous Q&A we stated that a non-bathing area does not carry a sweating prohibition. On the other hand, however, a Sauna is a room specifically associated for sweating simialr to a bathhouse.
 SSH”K 14 Footnote 68; Piskeiy Teshuvos ibid footnote 180
 See Minchas Yitzchak 5:32
 Piskeiy Teshuvos 326:16
 Piskeiy Teshuvos 326:16 footnote 184