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 Simethicone 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 Simethicone near the end of a label is present in tiny amounts and matters far less than the same ingredient near the top.
About Simethicone
It is a silicone, used to smooth, blur, and give a soft-focus finish. A silica-modified silicone rated 1/5, fungal-acne safe.
Simethicone in makeup and skincare
It is everywhere in primers, foundations, and 'blurring' complexion products, and in serums and moisturisers. Its irritancy is rated separately at 0/5, which is low.