What it is
Liquefied petroleum gas is a mixture of low-molecular-weight hydrocarbons, typically propane, butane, and isobutane, held as a liquid under pressure inside the can. When the valve opens, it flashes to gas and pushes the product out as a fine spray or mist, which is why it appears in aerosol sunscreen sprays. It acts purely as a delivery propellant and is not intended to remain on the skin in meaningful amounts.
Safety & warnings
As a volatile hydrocarbon propellant it is flammable, so aerosol cans carry standard pressurized-container handling precautions and should be kept away from heat and flame. Because it flashes off rapidly on dispensing, very little remains on skin; inhalation of the spray cloud is the main practical concern, so users are advised to avoid spraying near the face and to apply in ventilated areas.
Origin & sourcing
Synthetic in the sense of being industrially refined; the hydrocarbons are obtained from petroleum and natural gas processing and then purified for cosmetic aerosol use.
Questions everyone asks
What does liquefied petroleum gas do in a sunscreen?
It is the propellant in aerosol spray sunscreens, providing the pressure that turns the formula into a fine mist when you press the nozzle. It is not a skincare active and largely evaporates on contact with air.
Is the propellant left on my skin?
Very little. LPG flashes from liquid to gas almost immediately as it leaves the can, so the bulk of it disperses into the air rather than staying on the skin.