Creosote is not a single substance. It is a family of closely related chemical compounds, which come from natural sources. The most common type of creosote is coal-tar creosote utilized in industrial processes. Wood-tar creosote is also widely used and is familiar to homeowners as the black, oily substance lining fireplace chimneys. There are less common creosote varieties derived from water gas, peat moss, lignite and petroleum.


Wood-tar creosote was characterized chemically in the early 1800s by a German scientist, Carl Reichenbach. He found that its antiseptic and preservative properties were derived from the pyroligneous acids contained within creosote.

One of the primary properties of creosote or creosote oil is that it sinks in water. Depending on what substance it was derived from, it also maintains viscosity at very low temperatures and boils around 200 degrees Celsius. It is highly resistant to dissolution in water.

Wood-tar creosote predominantly contains plant phenolics and complex phenols, including methyl ethers. The high concentration of methyl ethers is a main differentiator between wood-tar and coal-tar creosotes. Most wood-tar creosote is derived from beechwood.


Derivatives of the creosote bush were used by southwest Native American tribes as medicines for treating sores, snakebites and gastrointestinal conditions. Cedar tree oil, which contains many compounds found in wood-tar creosote, found use throughout Europe for treating a wide variety of maladies including toothache, parasitic infections and skin diseases. Wood-tar creosote is the active preservative and flavoring component for meat that is dried and smoked with a wood fire.


Creosote’s main value is as a wood preservative. Most wood preservatives that use creosote utilize coal-tar creosote, which is more effective than wood-tar creosote for this purpose.

Wood-tar creosote also finds uses at the consumer level. It is the main ingredient in a handful of meat flavouring products. A derivate of wood-tar creosote, known generically as guaifinesin, is the main ingredient in most over the counter cough medicines. Seirogan is a popular medicine in Japan used as an anti-diarrheal whose main ingredient is wood-tar creosote.

Since the mid-1800s, creosote was used to protect railroad ties, utility poles and marine pilings from wood rot. It was also used for lamps, but only outdoors as burning it produced a black, oily smoke. Despite the much higher toxicity of coal-tar creosote, it still found medical use as a caustic agent and antiseptic well into the 20th century.

Today, coal-tar creosote’s natural water repellency and toxicity to fungus and insects still makes it ideal as a wood preservative in industrial and consumer applications. However, due to its highly toxic nature, its application has been limited to professionals by regulation in both Europe and North America.


The black, shiny creosote that can build up in fireplace or woodstove flues is similar to commercial wood-tar creosote except that it usually contains more carbon. It accumulates when firewood is burned at too low a temperature that prevents complete combustion. This usually comes about because of poor draft or using unseasoned wood. Highly efficient woodstoves resist creosote buildup.

When creosote accumulates on the sides of a chimney, a self-reinforcing effect is created. As the chimney narrows due to the buildup, draft is reduced, which further reduces full combustion, which leads to further creosote accumulation.

A hot fire may ignite the chimney creosote at any time. Creosote has a very high burning temperature, so the resulting chimney fire may cause the home’s structure to catch fire also. In fact, about a quarter of residential fires are caused by chimney fires due to creosote buildup. Thus, regular inspection of chimney flues by qualified chimneysweeps is highly recommended.

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