Creosote is not a single chemical but a mixture of hundreds to over a thousand individual compounds, and its exact composition depends entirely on which type of creosote you are talking about. The word refers to at least two very different industrial products: coal tar creosote, a dark oily preservative distilled from coal tar and used to treat railroad ties and utility poles, and wood creosote, a lighter liquid distilled from burning beechwood or similar hardwoods. To make things more confusing, the “creosote bush” of the American Southwest produces its own resin with yet another chemical profile. All three share a name and a smoky, tarry smell, but their compositions and uses diverge sharply.
Coal Tar Creosote, the Most Common Industrial Form
When most people say “creosote,” they mean coal tar creosote, the thick, yellowish-to-black oil that has been pressure-treated into wooden railroad ties, telephone poles, and marine pilings for well over a century. It is produced by heating coal tar, itself a byproduct of coking coal at high temperatures, and then distilling specific fractions from it. The result is staggeringly complex. Advanced analytical methods have detected over 1,500 individual compounds in a single sample of coal tar creosote, far exceeding earlier estimates that placed the number in the low hundreds.1PubMed. Comprehensive composition of Creosote using comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GCxGC-TOFMS)
Despite that complexity, the compounds fall into a few broad chemical families. The largest group is polycyclic aromatic hydrocarbons, or PAHs. These are molecules built from fused rings of carbon and hydrogen atoms. Naphthalene (two rings, the same chemical used in old-fashioned mothballs) is one of the most abundant. Phenanthrene and anthracene (three rings each), fluoranthene and pyrene (four rings), and benzo[a]pyrene (five rings) are all present in meaningful quantities. The heavier PAHs, those with four, five, or six rings, tend to be more persistent in the environment and more concerning for health.
Alongside the PAHs sit phenolic compounds, tar acids, and heterocyclic compounds containing nitrogen, sulfur, or oxygen atoms in their ring structures. Phenol itself is present, along with cresols (methylphenols) and xylenols (dimethylphenols). There are also smaller amounts of non-aromatic hydrocarbons and trace metals. The exact proportions shift depending on the source coal, the distillation temperature, and how the product was blended. No two batches of coal tar creosote are chemically identical, which is one reason pinning down precise percentages for the mixture as a whole is so difficult.
Wood Creosote Has a Very Different Profile
Wood creosote, sometimes called beechwood creosote, is produced by the destructive distillation of wood rather than coal. The chemical makeup reflects that origin. Instead of being dominated by heavy PAHs, wood creosote is rich in simple phenolic compounds. An analysis of beechwood creosote found its major volatile constituents to be guaiacol (about 25%), 4-methylguaiacol (about 21%), m-cresol (roughly 8%), p-cresol (roughly 8%), o-cresol (about 5%), and phenol (about 3%).2Journal of the Science of Food and Agriculture. Antioxidant activity and characterization of volatile constituents of beechwood creosote
Guaiacol and its relatives give wood creosote its distinctive smoky aroma. These are the same family of molecules responsible for the flavor of smoked meats and cheeses. In Japan, a refined form of wood creosote called seirogan has been used for over a century as a folk remedy for diarrhea and intestinal discomfort. Because its PAH content is minimal compared to coal tar creosote, wood creosote carries a very different risk profile. The two products share a name and a general “tarry” character, but confusing them is a real mistake when evaluating safety.
Why the Composition Matters for Wood Preservation
Coal tar creosote’s chemical complexity is actually the source of its effectiveness. It has been used for over a hundred years as a fungicide, insecticide, and sporicide, applied by pressure methods to railroad ties and utility poles.3ENVIRONMENT. TECHNOLOGY. RESOURCES. Proceedings of the International Scientific and Practical Conference. Review of Creosote Pollution Toxicity and Possibilities of Bioremediation The PAHs are inherently toxic to fungi and insects, and the phenolic compounds add antimicrobial punch. Together, the mixture penetrates deep into wood fibers under pressure and resists leaching because many of the heavier PAH components are nearly insoluble in water. A railroad tie treated with creosote can last 30 years or more in the ground, which is why it remained the dominant wood preservative for outdoor infrastructure through most of the 20th century.
The flip side of that durability is persistence. Creosote-treated wood slowly releases its chemical payload into the surrounding soil and groundwater over decades. Those heavier PAHs, the four-to-six-ring molecules, are the slowest to break down. Phenanthrene, a three-ring PAH commonly found in creosote-contaminated sites, binds tightly to soil particles. In contaminated aquifer material, most of the compound remained either extractable with solvents or bound to soil after nearly two months, with very little evaporating away.4PubMed. Pentachlorophenol and phenanthrene biodegradation in creosote contaminated aquifer material This stubbornness is the central tension of creosote: the same chemical persistence that makes it an excellent preservative also makes it a long-lived environmental contaminant.
Health Risks Tied to Specific Compounds
The health concerns around coal tar creosote trace directly back to its PAH content. PAHs, especially the heavier ones like benzo[a]pyrene, are well-established carcinogens. They cause cancer by reacting with DNA. When researchers applied coal tar and creosote to the skin of mice, they found that the compounds formed DNA adducts, meaning PAH molecules physically bonded to the DNA strand. The damage pattern was characteristic of polycyclic aromatic hydrocarbons specifically. Mouse skin showed a phase of rapid repair in which roughly half to two-thirds of the adducts were cleared within seven days, followed by a much slower phase where the remaining damage took weeks to resolve.5Carcinogenesis. Covalent binding of components of coal-tar, creosote and bitumen to the DNA of the skin and lungs of mice following topical application With repeated exposure, DNA adducts accumulated toward a steady-state level, which helps explain why chronic occupational contact carries more risk than a brief encounter.
The International Agency for Research on Cancer classifies coal tar creosote as a probable human carcinogen. Skin cancer among creosote workers was documented as early as the 19th century, and modern epidemiological studies have associated long-term exposure with elevated rates of skin, lung, bladder, and lip cancers. The risk is driven overwhelmingly by those larger PAH molecules. Naphthalene, which is the most abundant single component by weight in many creosote blends, is less potent as a carcinogen than its heavier cousins but contributes to respiratory irritation and hemolytic anemia at high exposures.
How Workers Actually Absorb Creosote
Because creosote is a mixture of compounds with wildly different physical properties, the way it enters the body varies by component. The lighter, more volatile compounds like naphthalene evaporate readily and are inhaled. The heavier PAHs stick to surfaces and skin. For workers at creosote treatment plants, dermal absorption turns out to be the dominant route. A study of creosote workers measured urinary 1-hydroxypyrene, a metabolite of pyrene, and found that the amount excreted was up to 50 times greater than what could be accounted for by inhaled pyrene alone. That gap points to massive skin absorption.6Occupational and Environmental Medicine. Significance of dermal and respiratory uptake in creosote workers: exposure to polycyclic aromatic hydrocarbons and urinary excretion of 1-hydroxypyrene
Even on Monday mornings, before workers had handled any creosote that week, their urinary 1-hydroxypyrene levels were already elevated, reflecting the slow clearance of PAH metabolites from the body over the weekend. Levels tended to build across the working week and peaked in the evening after a shift rather than immediately at end of shift, consistent with the delayed absorption kinetics of skin contact. Workers who assemble impregnated railway sleepers, not just those who run the impregnation process itself, show similar metabolite excretion patterns.7PubMed. Inhalation and dermal exposure of workers during timber impregnation with creosote and subsequent processing of impregnated wood The practical upshot is that gloves and skin protection matter at least as much as respiratory masks for people who work with creosote-treated wood.
Cleaning Up Creosote Contamination
Former creosote treatment plants are among the most chemically complex contaminated sites to remediate. The soil and groundwater at these facilities can contain the full spectrum of creosote compounds, from volatile naphthalene near the surface to dense pools of heavier PAHs deeper underground. Traditional approaches include excavation and incineration, which work but are expensive and destructive to the site.
Biological approaches have shown promise. Certain wood-rotting fungi can break down PAHs in contaminated soil. In a laboratory study, the oyster mushroom fungus degraded PAHs with measurable efficiency, removing roughly 55 to 67% of total PAHs from creosote-contaminated soil over 120 days. It was especially effective against the smaller two-ring and three-ring compounds, removing over 85% of them, while still making a dent in the harder-to-degrade four-to-six-ring PAHs. The fungus also appeared to stimulate the growth of certain soil bacteria that themselves contribute to PAH breakdown.8PubMed. Fungal bioremediation of the creosote-contaminated soil: influence of Pleurotus ostreatus and Irpex lacteus on polycyclic aromatic hydrocarbons removal and soil microbial community composition in the laboratory-scale study This kind of synergy between fungi and bacteria is an active area of research for dealing with old creosote sites without simply moving the contamination somewhere else.
The Creosote Bush Is Something Else Entirely
If you live in the desert Southwest of the United States or northern Mexico, “creosote” might first bring to mind the creosote bush, Larrea tridentata, a scrubby evergreen shrub that dominates vast stretches of arid landscape. It earned its common name because crushing its leaves releases a pungent, tarry smell reminiscent of coal tar creosote. But the plant’s chemistry has nothing to do with coal tar or PAHs.
The principal phenolic compound in the creosote bush’s leaf resin is nordihydroguaiaretic acid, or NDGA, a potent antioxidant.9Biochemical Systematics and Ecology. Plant Nordihydroguaiaretic acid: inter- and intrapopulational variation in the sonoran desert creosote bush (Larrea tridentata, zygophyllaceae) NDGA concentrations are highest in the leaves and green stems of the plant.10Biochemical Systematics and Ecology. Distribution and concentration of total phenolics, condensed tannins, and nordihydroguaiaretic acid (NDGA) in creosotebush (Larrea tridentata) The compound was once used as a food preservative in the United States because of its ability to prevent fats from going rancid, though it was later withdrawn over concerns about liver toxicity at high doses. Indigenous peoples of the region have used creosote bush preparations medicinally for centuries, brewing teas and poultices from the leaves. NDGA continues to attract research interest for its antioxidant and anti-inflammatory properties, and the plant itself produces a broader cocktail of phenolics and condensed tannins throughout its tissues.11PubMed. Larrea tridentata (Creosote bush), an abundant plant of Mexican and US-American deserts and its metabolite nordihydroguaiaretic acid
The chemistry of the creosote bush is worth knowing about precisely because the name overlap causes confusion. If someone mentions “creosote” in a conversation about cancer risk or wood treatment, they almost certainly mean coal tar creosote. If they mention it while hiking in the Sonoran Desert or discussing herbal medicine, they mean the plant. The substances have essentially nothing in common beyond the smell.
Creosote Compounds in Your Food
Some of the same phenolic molecules found in wood creosote show up in smoked foods and commercial liquid smoke products. Guaiacol, syringol, and their methylated relatives are the compounds that give barbecue and smoked salmon their characteristic flavor. An analysis of commercial liquid smoke found that phenolic compounds accounted for about a third of the detected chemical signal, with syringol as the most abundant, followed by guaiacol and pyrocatechol.12PubMed Central. Chemical characterization of commercial liquid smoke products
This connection is not a coincidence. Liquid smoke is literally made by condensing wood smoke, the same process that produces wood creosote. The difference is one of refinement and concentration. Commercial liquid smoke is filtered and processed to remove tarry residues and minimize PAH contamination, leaving behind mostly the lighter phenolic flavor compounds. Wood creosote, as described earlier, is dominated by the same guaiacol family. Coal tar creosote, by contrast, is much heavier on PAHs and would be genuinely dangerous to consume. So while it is technically accurate to say that your smoked brisket contains some of the same chemicals as creosote, the relevant comparison is to wood creosote’s phenolic fraction, not to the PAH-laden industrial product soaking into railroad ties.
Why “Creosote” Keeps Meaning Different Things
The word “creosote” derives from the Greek words for “flesh” and “to save,” a reference to the preservative qualities of the original wood-derived product identified in the 1830s. As coal tar became industrially abundant during the 19th century, the name was applied to the coal-derived distillate as well, despite its fundamentally different composition. The creosote bush picked up the label from European settlers who noticed the tarry smell of its resin. And the black, crusty buildup inside chimneys and wood stoves, also commonly called creosote, is yet another substance entirely: a mix of condensed wood smoke, soot, and partially combusted organic compounds that accumulates when flue gases cool before exiting.
Each of these “creosotes” shares a phenolic, smoky odor because phenols and simple aromatic compounds are produced whenever organic material is heated or burned. But their chemical compositions range from the relatively simple phenolic profile of beechwood creosote to the more than 1,500 compounds identified in coal tar creosote to the NDGA-dominated resin of the desert shrub. Knowing which creosote someone is talking about is the first step to understanding what it is actually made of and whether you should be concerned about exposure to it.