Do not make (oil) like it, for it is holy… (Exodus 30:32)
The Torah gives the formula for making the special anointing oil, but we are adjured not to use this recipe to mix oil for any other purpose. This oil is holy, we are told, and so it shall remain.
Actually, the oil that was prepared by Moses was all the shemen hamishcha that was ever needed, prior to its being hidden away. The Talmud tells us (Horayos 11b and Kerisos 5a-b) that one of the miracles of the oil was that none it was ever lost through evaporation, absorption or use. They started with 12 logs (about four liters or one gallon) and they always had 12 logs.
Additionally, the Torah says (Exodus 30:21), “This (oil) will be to Me for all your generations,” suggesting that the batch prepared by Moses is all the anointing oil that would ever be needed. Aside from the straightforward meaning of the verse, the word “this” in Hebrew is “zeh.” The numerical value of zeh is 12, corresponding to those 12 logs of oil that Moses made.
The Torah gives us the reason right there in the commandment: It is holy and it shall remain holy to you. The word holy means separate or unique. For us to make similar oil for mundane purposes would make this recipe not unique for sacramental purposes.
This prohibition applies to both men and women in all times and places. Even though we do not currently have access to the real shemen hamishcha, we may not replicate it according to the formula given by the Torah. This mitzvah is discussed in the Talmudic tractates of Kerisos (5a) and is codified in the Mishneh Torah in the first chapter of Hilchos Klei HaMikdash. It is #83 of the 365 negative mitzvos in the Rambam’s Sefer HaMitzvos and #145 of the 194 negative mitzvos that can be fulfilled today as listed in the Chofetz Chaim’s Sefer HaMitzvos HaKatzar.