Air fresheners are consumer products that typically emit fragrance and are used in homes or commercial interiors such as restrooms, foyers, hallways, vestibules and other smaller indoor areas, as well as larger areas such as hotel lobbies, auto dealerships, medical facilities, public arenas and other large interior spaces. Car fresheners are used in automobiles. As a source of odors, specific deodorizing blocks are made for toilets and urinals. There are many different methods and brands of air fresheners. Some of the different types of air fresheners include electric fan air fresheners, gravity drip hygiene odor control cleaning systems, passive non-mechanical evaporating aroma diffusers, metered aerosol time-operated mist dispensers, sprays, candles, oils, gels, beads, and plug-ins. Some air fresheners contain chemicals that provoke allergy and asthma symptoms or are toxic. Air freshening is not only limited to modern day sprays, air freshening also can involve the use of organic and everyday house hold items. Although air fresheners are primarily used for odor elimination, some people use air fresheners for the pleasant odors they emit. History Fragrances have been used to mask odors since antiquity. A variety of compounds have been used over the past two millennia for their abilities to create pleasant aromas or eliminate unpleasant odors. The first modern air freshener was introduced in 1948. Its function was based on a military technology for dispensing insecticides and adapted into a pressurized spray using a chlorofluorocarbon (CFC) propellant. The product delivered a fine mist of aroma compounds that would remain suspended in the air for an extended period of time. This type of product became the industry standard and air freshener sales experienced tremendous growth. In the 1950s, many companies began to add chemicals that counteract odors to their fragrance formulas. These chemicals, intended to neutralize or destroy odors, included unsaturated esters, pre-polymers, and long-chain aldehydes. In the 1980s, the air freshener market shifted away from aerosols, due to concerns over the destruction of the ozone layer by chlorofluorocarbons (CFCs). Many other air freshener delivery methods have become popular since, including under the seat wafer air fresheners, scented candles, reed diffusers, potpourri, and heat release products. Basic principles The control of odors is addressed by five classes of mechanisms; Adsorption: Adsorbents like zeolite, activated charcoal, or silica gel may be used to remove odors. Oxidation: ozone, hydrogen peroxide, peroxide, chlorine, chlorate and other oxidizing agents can be used to oxidize and