Included in the prohibition to engage in one’s needs before the prayer service is the prohibition to get a haircut or to enter a bathhouse (Rambam Tefillah 6:7). However, to wash one’s hands is an obligation. It is also proper to wash one’s face and brush one’s teeth before praying (Shulchan Aruch 4:17; 46:1).
It is permissible to ritually immerse oneself in a mikveh before praying since there is no affront to the respect due to prayer. In fact, just the opposite is true – it is a preparation and purification towards it.
Similarly, it is permissible to take a shower before praying, since the washing of one’s whole body in nine kabin of water, which is approximately 12.5 liters (approximately 3.3 US liquid gallons), also constitutes a preparation and purification towards prayer (see Shulchan Aruch, Orach Chaim 88:1; Mishnah Berurah 89:4; Minchat Yitzchak 4:21).
According to a number of poskim, it is prohibited for the person who is bathing to wash himself with soap before prayer because that kind of washing is included among the types of prohibited bathing. However, in practice, one who feels that he is dirty and his intention is to become clean, and not to pamper himself, may wash his body with soap on condition that he does not arrive late to the minyan because of this.
Likewise, it is prohibited to get a haircut before prayer; however, regarding shaving there is uncertainty. There are those who say that shaving is included in the ruling against haircuts. However, it seems that the halachah is that a person who normally shaves every day is allowed to shave before prayer, since shaving for him is one of the regular morning waking activities and is not considered tending to one’s own needs before prayer. It is especially proper to permit such an act if it is done as preparation for prayer.
. Ishei Yisrael 13:21 writes that it is prohibited to wash oneself with soap. Yalkut Yosef 89:30 writes that it is not proper to shower, but if this helps him pray with kavanah and in cleanliness, it is permitted, though he should not use a lot of soap. Halichot Shlomo 2:8 rules that it is not proper to use soap. He explains that there is concern that soaping oneself will lead him to take a bath, which is forbidden. However, in paragraph 11 he writes that if the time of his regular minyan has not yet arrived, perhaps there is no prohibition to wash before prayer (as brought in the previous note).The essence of the rationale for leniency in this case is that in earlier times, ordinary bathing, to which the Chachamim refer, was known to last a while, was intended for enjoyment, and required lengthy preparations, such as starting a fire, heating the water, or walking to a bathhouse. However, a quick shower is done essentially to rid oneself of dirt and perhaps to invigorate oneself as well, and therefore there is no prohibition concerning it. Further, the Rambam (Hilchot Tefillah 4:3) writes that there is an obligation to wash one’s face, hands, and feet before praying Shacharit. See Beit Yosef 92 who clarifies his source and although he writes that in practice it is not customary to wash one’s feet, nevertheless we can learn from the Rambam that washing for cleanliness before prayer is considered an enhancement of the mitzvah. Additionally, according to the Kolbo, there is no prohibition against bathing oneself and getting haircuts before prayer, and only other activities are forbidden. His opinion is brought by Eliyah Rabbah and Kaf HaChaim 89:53. It seems that his reasoning is that bathing constitutes preparation in honor of the Shacharit prayer. Although we do not actually rule like him on the matter of bathing and haircuts, with regard to a short shower with soap, one may be lenient. In addition, when there is doubt concerning a rabbinic prohibition, the halachah follows the lenient opinion.