What a 1/5 rating means
On the comedogenic scale, a 1 sits at the safe end of the scale — clogging is unlikely for most people. That places Magnesium Stearate in the range most people, including many with acne-prone skin, tolerate well.
One thing the number cannot tell you is concentration. Ingredients are listed in descending order, so Magnesium Stearate near the end of a label is present in tiny amounts and matters far less than the same ingredient near the top.
About Magnesium Stearate
It is a mineral-based ingredient, common in pigments and sun protection. A stearate salt used as a bulking and anti-caking agent in powders, rated 1/5.
Magnesium Stearate in makeup and skincare
It is central to mineral makeup, pressed powders, and mineral sunscreens. Its irritancy is rated separately at 0/5, which is low.
If you deal with fungal acne (malassezia folliculitis) rather than ordinary clogged pores, note that Magnesium Stearate is among the fatty-acid or ester-type ingredients that community sources commonly avoid — a separate concern from its comedogenic score, and one with weaker evidence behind it.