What it is
This is a light, volatile hydrocarbon gas liquefied under pressure and used to expel product from aerosol cans. In spray sunscreens it provides the pressure that delivers the formula as a fine mist and then evaporates rapidly. It is functional packaging chemistry and is not a UV filter, so it contributes no sun protection.
Safety & warnings
Isobutane is highly flammable, so aerosol sunscreens containing it should be kept away from heat, flame, and ignition sources, and should not be applied near open flame. Inhalation of spray mist should be avoided by not spraying directly on the face and by using in well-ventilated areas. On skin it is essentially non-irritating because it evaporates almost immediately after application.
Origin & sourcing
Synthetic hydrocarbon obtained from petroleum and natural gas processing.
Questions everyone asks
Why is isobutane in spray sunscreen?
It is the propellant that pushes the sunscreen out of the can as a mist; it evaporates quickly and does not stay on the skin.
Is it flammable?
Yes. It is a flammable gas, so aerosol sunscreens with isobutane should be kept away from flame and heat and not applied near ignition sources.