These markers are generally used on hard, non-porous surfaces, because instead of staining they form a surface layer that can be removed by high pressure cleaning or paint thinners. Organic solvents such as acetone, xylene, or toluene, Isopropyl alcohol, ethanol and ethyl acetate are preferred cleaners when used indoors, as their fumes are much less hazardous than toluene and xylene, the main components of paint thinner, or longer-chain hydrocarbons found in mineral spirits. Other common non-polar solvents include benzene, turpentine and other terpenes (which constitute essential oils of many plants with strong scents), most ethers, chloroform and dichloromethane, hydrocarbon fuels, and diacetone alcohol, among many others. Note that most of these solvents are very flammable, and/or their concentrated vapors are harmful to health.