What it is
Butane is a small, volatile hydrocarbon that is liquefied under pressure inside an aerosol can. When the valve is opened, it expands to gas and expels the product as a spray or foam. It is frequently used together with related gases such as propane and isobutane to tune the spray pressure of aerosol sunscreens and other personal care products.
Safety & warnings
As a propellant, butane is sealed in the can and largely flashes off on dispensing, so little remains on skin. It is extremely flammable, so aerosol products containing it must be kept away from flames, sparks, and heat, and should not be sprayed near an open flame. Intentional inhalation of the concentrated gas is hazardous.
Origin & sourcing
Synthetic; a petroleum- or natural-gas-derived hydrocarbon refined to cosmetic-grade purity.
Questions everyone asks
Why is butane in my spray sunscreen?
It acts as the propellant: liquefied under pressure in the can, it expands to gas to push the product out as a fine spray.
Does butane stay on my skin?
Very little does; as a volatile gas it largely evaporates on contact, leaving the actual sunscreen film behind.