Creosote or pitch oil is the name used for a variety of products that include wood creosote and coal tar creosote. The word is also used to describe the black oily accretion that builds up inside of chimney flues as a result of incomplete burning of wood or coal. Commercially, wood creosote is created by high temperature treatment of beech and other woods, or from the resin of the creosote bush.
Coal tar creosote is an EPA-registered wood preservative. It is distilled from crude coke oven tar, and is mainly composed of polycyclic aromatic hydrocarbons (PAHs), but also contains phenols and cresols.
Wood creosote is a colourless to yellowish greasy liquid with a smoky odor and burned taste. Other than looks and taste, the chemical makeup is totally different from coal tar creosote. It is made of plant phenolics rather than petrochemicals: guaiacol, creosol, o-cresol, and 4-ethylguaiacol.
Wood creosote has been used as a disinfectant, a laxative, and a cough treatment, but these have mostly been replaced by newer medicines.
The popular Japanese Kampo anti-diarrhea medicine Seirogan has 133 mg wood creosote (from beech, maple or oak wood) per adult dose as its primary ingredient. 
Wood creosote also protects wood from shrinking from the sun, losing its colour and moulding from the rain. Many companies use creosote to protect wood.
Coal tar creosote
Another form of creosote is coal tar creosote. Coal tar creosote is the most widely used wood preservative in the world. It is a thick, oily liquid typically amber to black in colour. The American Wood Preservers' Association states that creosote "shall be a distillate derived entirely from tars produced from the carbonization of bituminous coal." Coal tar used for certain applications may be a mixture of coal tar distillate and coal tar. See, AWPA Standards
The prevailing use of creosote is to preserve wooden utilities/telephone poles, railroad cross ties, switch ties, and bridge timbers from decay. Due to its carcinogenic character, the European Union has regulated the quality of creosote for the EU market  and requires that the sale of creosote be limited to professional users.
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