What is Simethicone?
Chemically, Simethicone is a silicone. A silica-modified silicone rated 1/5, fungal-acne safe.
Where Simethicone shows up
Simethicone is commonly formulated into primers, serums, moisturisers, and hair products, where it smooths and blurs. Separately from clogging, its irritancy is rated 0/5 — low, so it's unlikely to sting or sensitise on its own.
Is Simethicone bad for acne-prone skin?
That low score makes Simethicone a reasonable choice even for acne-prone skin. As always, individual reactions vary, but it is not a likely cause of clogged pores.