Isobutane

This ingredient is a low-molecular weight gas using as a propellant in foams, sprays, and mousses.

It is not intended to interact with skin in a meaningful way as it evaporates almost immediately after dispensing and only leaving behind the actual product formula.

If it does somehow make it onto your skin, it is chemically inert and does not penetrate or get absorbed into skin. Safety assessments note that adverse skin reactions to this ingredient are uncommon.