Butane is a highly volatile, colorless hydrocarbon gas, commonly used as an aerosol propellant in many household and personal care products. It is easily liquefied under moderate pressure for storage and transport in aerosol cans. While butane is well-known as a fuel source, its primary role in cosmetics is as an efficient propellant. Butane is generally considered safe when applied as directed, but misuse can lead to acute physical harm.
Butane’s Function as a Product Propellant
Butane is incorporated into aerosol products like deodorants, dry shampoos, shaving foams, and sunscreens because it is a low-cost, effective means of delivering a fine mist. As a compressed, liquefied gas, it is mixed with the active ingredients inside the pressurized can. Upon pressing the nozzle, the pressure difference forces the liquid-propellant mixture out.
The butane rapidly changes from its pressurized liquid state back into a gas once it leaves the nozzle and hits the air. This quick phase change is the mechanism that atomizes the liquid formula, creating the fine, evenly distributed spray the user experiences. This rapid vaporization minimizes contact time with the skin, allowing the butane to dissipate almost instantly while the active ingredients are deposited. Butane and related hydrocarbons became widespread as they replaced older propellants, such as chlorofluorocarbons, for environmental reasons.
Immediate Physical Effects of Butane Exposure
The greatest risk to the skin from butane is not chemical toxicity but a physical hazard known as evaporative cooling. Butane has an extremely low boiling point, requiring a significant amount of heat energy to vaporize quickly. When the liquefied butane is sprayed, it draws this necessary heat from the nearest source—the skin—causing a rapid, intense drop in temperature.
If an aerosol product is sprayed too closely or held directly against the skin, the temperature can drop drastically, sometimes to -40°C or lower. This extreme cold can cause frostbite, a freezing injury to the tissue. Cases of deep frostbite requiring skin grafts have been reported from the misuse of products containing butane and propane propellants. To avoid this acute cold injury, users should always apply aerosol products from the recommended distance, allowing the butane to fully evaporate before reaching the skin.
Butane is also a hydrocarbon, which means it possesses solvent properties. This characteristic allows it to dissolve and remove the skin’s natural surface oils, or sebum. Repeated or prolonged exposure can strip the skin of these protective lipids. Over time, this defatting action can lead to increased dryness, mild irritation, or a compromised skin barrier function.
Safety Profile and Cosmetic Approval
Butane is considered safe for its intended use in cosmetics by major regulatory and safety bodies. The Cosmetic Ingredient Review (CIR) Expert Panel has assessed butane and concluded it is safe when used as a cosmetic ingredient in current concentrations. The U.S. Food and Drug Administration (FDA) has also affirmed butane and its isomers as generally recognized as safe for use in certain applications.
The risk of skin absorption and systemic toxicity is considered low because butane is highly volatile and evaporates almost immediately upon contact. Scientific assessments estimate that the propellant remains on the skin for no longer than about ten seconds. Butane is not generally recognized as a common skin sensitizer or allergen, meaning it rarely causes allergic reactions or irritation in normal use. Regulatory approval is contingent on the purity of the gas, ensuring that harmful trace contaminants like butadiene are controlled to safe levels.