According to a March 2008 article in "The Sunday Times," the popularity of dry shampoos is on the rise, and no wonder: these spray-on hair products absorb excess grease and can give volume to hair, even days after washing. They can help hair look clean and refreshed and make quick styling easier. Although there are a wide variety of dry shampoos on the market--ranging from the very affordable to the very expensive--all spray-style dry shampoos contain a basic set of ingredients: aerosol propellants, absorbing agents, solvents, conditioning agents, fragrance, preservatives and emulsifying agents.
Aerosol Propellants
Butane, isobutane and propane are commonly used in dry shampoos as aerosol propellants. All three are types of colorless, odorless compressed gases that can be used to propel or spray ingredients out of bottles fitted with a spray nozzle dispenser. Some commercial dry shampoos are non-spray fluids that must be massaged into the hair; these do not contain any aerosol propellants. However, all spray-style dry shampoos contain at least one of these aerosol gasses.
Absorbing Agents
One of the primary functions of a dry shampoo is to absorb accumulated grease from both the hair and scalp. The most common absorbing agents utilized are oryza sativa starch, aluminum starch octenylsuccinate, zea mays starch and silica. According to Cosmeticsinfo.org, oryza sativa starch is a compound isolated from rice and capable of binding to and removing excess liquid such as grease. aluminum starch octenylsuccinate is a modified starch that can also act as an anti-caking agent in fluid products, while silica is the mineral silicon dioxide. Zea mays starch is derived from corn plants.
Solvent
The different ingredients contained in the most common spray-style dry shampoos must have a solvent, or liquid substance, that the various components can be dissolved into. For most dry shampoos, this solvent is alcohol denat. Alcohol denat. is ethanol that, by law, must be denatured--combined with a denaturant substance that makes it bitter to the taste--when used in products not meant for consumption. The alcohol denat. dissolves the dry shampoo's ingredients and thins them into a liquid suitable for spraying.
In some dry shampoos, Cyclomethicone may be added as an additional solvent. Cyclomethicone works best as a base solvent for fragrance ingredients.
Conditioning Agents
Dry shampoos contain hair conditioning or moisturizing agents to keep hair smooth and supple. Distearyldimonium chloride, avena sativa kernel oil and isopropyl myristate are the most common conditioning compounds used.
Fragrance
A number of ingredients are used to produce a pleasant dry shampoo smell, from coumarin, a naturally occurring compound that gives off a nutty, vanilla, grass-like scent, to linalool, limonene, citronellol and extracts of fruits such as grapefruit or tangerine.
Preservatives
A number of ingredients included in dry shampoos prevent the deterioration of the components or fragrance of the shampoo. Two of the most common include cyclodextrin and benzyl alcohol.
Emulsifying Agents
Some dry shampoos contain emulsifying agents such as magnesium stearate or PPG-3, also known as dimethicone. These emulsifiers keep the different ingredients within the solution from separating, making a smooth, easily sprayed fluid.
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