The continuation is stronger than the beginning.

The Shaykh : For this reason, the scholars (may Allah have mercy on them) derived from this Sunnah that continuation is stronger than beginning. This continuation is stronger than starting anew. Therefore, it is permissible to continue the effect of perfume during the state of ihram, but it is not permissible to start using it. It is permissible for a man to resume relations with his divorced wife while he is in ihram, but it is not permissible for him to marry. Why? Because continuation is stronger than beginning. It is permissible for ownership of game to continue after entering ihram, but it is not permissible to hunt while in ihram. There are examples of this. The important point is that the remaining effect of perfume after entering ihram does not cause harm. If someone were to say: "Does this imply that if the perfume is on the head, as in the hadith of A'ishah, a person must touch his head when wiping it?" The answer is: Even if that were required, it would not cause harm, because this person in ihram did not start using the perfume; rather, the perfume he used before entering ihram remained. He is inevitably required to wipe his head, so it does not cause harm. Yes, if he intentionally touches his head while the perfume is on it and it is wet, this is not permissible. But if he performs wudu, he must touch it. Yes.