All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
If the antiperspirant does not contain perfume, then there will be no expiation for using it after assuming Ihram for Hajj or ‘Umrah. If it contains perfume and you used it after assuming Ihram, then an expiation is due on you even if you did this before reaching the Meeqat because assuming Ihram is valid and in effect before reaching the Meeqat, regardless of the fact that it is preferable to postpone it till you reach it.
If you used an antiperspirant that contains perfume after putting on your Ihram clothes and before assuming Ihram for Hajj, then no expiation will be due on you.
The expiation is to choose to make one of three: to slaughter a sheep in the Sanctuary and distribute its flesh on its poor inhabitants, to feed six needy persons each with half a Sa‘ (3 liters – of foodstuff), or to fast three days.
Allaah Knows best.