Any form of washing for the sake of pleasure is forbidden on Tish’a B’Av, whether the water is hot or cold. One may not even wash a small part of his body; it is even forbidden to dip one finger in water. But someone who got mud, feces, or blood on himself may wash the soiled area, because his intention is not to pamper himself (Sh.A. O.C. 554:9). Similarly, a woman who needs to change her child’s diaper may wash the soiled area, even though her hand will get washed in the process. She may even use soap if the filth or odor does not come off with water alone.
A woman who is preparing food with which to break the fast, or for her children, may rinse food items or dishes, because she is not washing for the sake of pleasure. And even though some pleasure is derived every time one washes a soiled area of the body, it is not considered washing for the sake of pleasure, since her main intent is to remove the filth.
Someone who perspired excessively, to the point where he is very bothered and distressed, may wash the sweaty area, because his intention is not to get pleasure (M.B. 613:2, Sha’ar HaTziyun 4).
In addition, someone who is very sensitive and cannot orientate himself in the morning until he washes his face may do so with [plain] water. One who is always accustomed to using water to remove the crusty discharge that builds up in the eyes overnight may do so [on Tish’a B’Av] (Sh.A. 554:11, M.B. 22).
It is forbidden to rinse one’s mouth on Tish’a B’Av. Nevertheless, one who will be very distressed if he does not do so, may rinse out his mouth and brush his teeth, without toothpaste, on Tish’a B’Av. On Yom Kippur, however, when the obligation to fast is biblical, one should not be lenient on this issue (see above, 7.5, note 6).
A bride within the first thirty days of her marriage may wash her face and apply any lotion she needs, to avoid making herself unattractive to her husband (M.B. 554:29, Sha’ar HaTziyun 38).
One may take a slightly damp towel and run it across one’s face, hands, and feet, because the prohibition of washing does not apply to such a small amount of moisture. The only condition is that the towel not be tofei’ach al menat le’hatpi’ach, meaning, it cannot be so wet that it could moisten one’s hand to the extent that his hand could then moisten something else (Rama 554:14, M.B. 27).