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 Butylene Glycol 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 Butylene Glycol near the end of a label is present in tiny amounts and matters far less than the same ingredient near the top.
About Butylene Glycol
It is a humectant that pulls water into the upper layers of skin. A lightweight humectant and solvent rated 1/5, fungal-acne safe.
Butylene Glycol in makeup and skincare
It is a near-universal hydrator in primers, foundations, toners, and moisturisers. Its irritancy is rated separately at 0/5, which is low.