An aerosol hair spray is a personal grooming product that is used by women and men to facilitate better control of one's desired hairstyle. The sprays usually are packaged under pressure in aluminum or tin-coated-steel cans, and their ingredients consist of a variety of polymers, solvents, additives and propellants. The interior of the typical can contains a valve that is attached to a plastic tube and an external button. The propellant and the other ingredients are mixed inside the valve when this button is pressed, allowing the spray to be applied to one's hair in a fine mist.
The polymers and additives that are found in aerosol hair spray function as a type of mild glue to hold a person's hair in place. The most common polymer found in aerosol hair spray is known as polyvinylpyrrolidine (PVP). This is a diluted version of the same substance that holds together the wooden layers that comprise a sheet of plywood. Vinyl acetate is sometimes mixed with PPV (PVPVA) as a copolymer, which provides the benefit of greater hair control in humid conditions.
Plasticizing or silicone additives usually are mixed with PPV and PVPVA. These substances, often chemicals such as isopropyl myristate or diethyl phthalate, combine with the polymer to make the applied solution less stiff and brittle as it dries on an individual's hair. Other additives might include a variety of anti-corrosives that are intended to prevent the carrying solvent from rusting the inside of the can.
Aerosol hair spray solvents make up the greatest percentage of the can's ingredients. Water is many times the solvent of choice, which is why the anti-corrosive additives are required. Ethanol is sometimes included as a solvent, but in many places, its use is tightly regulated because of potential problems with air pollution and flammability. Air pollution has been a factor in the changing of ingredients in aerosol hair spray since the 1970s.
Hair sprays were first marketed to the public in the 1950s, and at the time, the propellants of choice were chlorofluorocarbon gasses (CFCs). CFCs were thought to be safe, but scientific research conducted over subsequent years determined that their release into the atmosphere very likely contributed to ozone layer depletion. CFCs have since been phased out of aerosol products made by major manufacturers.
The controversial and potentially dangerous CFCs were initially replaced by hydrocarbon propellants containing a mix of propane and butane. Hydrocarbons also were determined to pose a possible risk of ozone layer depletion, which led to the creation of hydrofluorocarbons (HFCs). As of 2011, most aerosol hair sprays utilize HFCs to propel the additives and polymers that keep one's hair looking fresh and well coiffed.