I didn’t know about logarithmic perception, that’s interesting! I bet you’re right about 7x being chosen due to the significance of the number seven in the Bible.

I haven’t heard that before but I don’t work on hair care products very often. Benzyl alcohol is used as a preservative in lots of cosmetic products though. It can be considered an allergen for some people, but overall it’s pretty safe (as far as we know so far).