Can one use deodorant on Yom Kippur? What if the reason is to remove sweat? Can you give us the source of the psak?
It is permitted to use deodorant if you will feel uncomfortable without it. Spray, rather than stick deodorant should be used.
Some authorities are mentioned as being stringent on this matter (see Ashrei Ish, Vol. 3, Chap. 71, no. 9, citing from Rav Elyashiv), but others are lenient (see Mikraei Kodesh 6 note 60; Chaim Sha’al 74:56; Machazeh Eliyahu, Kol Ha-Torah Vol. 51, p. 140), and where a person knows that he will suffer from bad odor, one can be lenient with spray deodorant.
Stick deodorant should not be used, because of the concern of sichah. Spray deodorant is distant from the concept of sichah (embalming with oils for pleasure), and is therefore certainly permitted for the purpose of dealing with bad odors.
[Although it is permitted to clean an area of the body that is soiled with water, and the same should apply even for stick deodorant for removing bad odors, the level of odor is hard to determine, and a person might come to apply deodorant without need. This is the reason why stick deodorant, which is closer to sichah, must be treated with added stringency.]
If a person does not suffer from bad odor, yet wishes to ‘smell good,’ deodorant should not be used on Yom Kippur.