Is it permissible to shower on Yom Tov, not for comfort just when you feel a terrible smell?
It is permitted to take a cold shower on YomTov (see Shulchan Aruch 326:1).
Under extenuating circumstances (such as three days of Yom Tov/Shabbos in the summer, which can happen for Rosh Hashanah, or two days for those who suffer from sweatiness), and where a cool shower is not a viable option (because this will involve significant discomfort), one can be lenient to take a warm shower.
Somebody who takes a shower (cold or warm) on YomTov must be careful to ensure that he does not run into related prohibitions. He must ensure that no fire will be lit or other system activated when the faucet it turned on, and cannot dry his hair vigorously (but can place a towel over the hair).
By contrast with times of bygone years, the idea of showering daily has become fairly universal, certainly in summer days; days when many bathed once a month or once a week are behind us.
This should apparently be reflected in the halachah of bathing on YomTov with hot water; bathing is no longer “eino shaveh le-chol nefesh” (something that is not done by everybody), and there seems to be little reason why it should be prohibited today.
Indeed, I have seen that RavYitzchakAbadi (Or Yitzchak, Orach Chaim 210) writes that it is permitted nowadays to heat water on YomTov for purposes of bathing, for this reason.
However, some poskim write that the halachah remains unchanged. The Be’er Moshe (8:159) is extremely sharp in this, and writes that he does not even want to consider the possibility of changing the halachah based on changes in social norms of washing. He proceeds to write that it is “entirely simple” that the prohibition remains in place.
Although he does not explain his reasoning, it appears that he sees the prohibition against washing as a rabbinic takanah (enactment), which we cannot permit based on social changes.
It is hard to accept this line of reasoning. We see from the Mishnah Berurah (511, in the biur halachah) that the halachah of smoking on YomTov changes based on social norms, and there is no apparent reason to think that the halachah of bathing shouldn’t change, too. The specific decree of a merchatz (bathhouse) will not apply to a shower in one’s private home (a private home is not a merchatz).
Indeed, when Rav Chaim Kanievsky was asked this question, he did not responded that the halachah cannot change, but wrote back that even today, bathing is not shaveh le-kol nefesh. Perhaps this is the case for BneiBrak, but for most of the world it is hard to say that showering, in particular for a summer’s two-day YomTov, is not shaveh le-kol nefesh.
Yet, although poskim were aware of the possibility, we do not find that most authorities are ready to be lenient. ShemirasShabbosKehilchasah (Chap. 14, note 21) brings up the point at length, and concludes with a tzarich iyun (requires further elucidation), whereas in the main section he rules in line with the basic Talmudic law. Rav Elyashiv, shlita, is likewise quoted in Shut Avnei Yashfei (3:55) as being stringent on this question.
It is possible that poskim do not wish to be lenient in this regard, for fear that leniency will lead to other pitfalls, such as in drying one’s hair, using soap, and so on. This is similar to the stringency mentioned by the Mishnah Berurah (326:21) concerning bathing in cold water on Shabbos.
Therefore, based on the rulings of poskim, it is hard to issue a blanket heter (leniency) on this matter. However, for extenuating circumstances, one can be lenient.