Mineral oil is another substance for which a single structural formula would be chemically misleading. CAS 8042-47-5 is used for highly refined mineral oils composed mainly of saturated hydrocarbons across a distribution of chain lengths and structures. Depending on refining and specification, the mixture can contain linear and branched alkanes and cycloalkanes. The important scientific question is therefore not "what is the molecule?" but "what molecules remain after refining, and in what proportions?"
Crude petroleum contains an enormous range of hydrocarbons, including aromatic species. Production of white mineral oil uses severe refining and purification to remove colored, odorous, reactive, and undesirable aromatic components, leaving a clear, chemically stable hydrocarbon mixture. This is why refining history matters so much to toxicology. "Mineral oil" is a broad petroleum-derived concept, while highly refined white mineral oils meeting pharmaceutical or food specifications are materially different from poorly refined historical oils.
Their chemical inertness and low water solubility support many uses. Highly refined grades can serve as lubricants, processing aids, protective films, cosmetic emollients, pharmaceutical excipients, and in selected jurisdictions food-related applications. The liquid spreads readily over hydrophobic surfaces and resists oxidation better than many unsaturated natural oils. Yet viscosity and molecular-weight distribution strongly influence migration, absorption, and performance, so one mineral-oil grade cannot automatically substitute for another.
Modern risk assessment reflects this compositional thinking. European assessments separate mineral-oil saturated hydrocarbons (MOSH) from mineral-oil aromatic hydrocarbons (MOAH). In 2023 EFSA concluded that current dietary exposure to MOSH did not raise a health concern across age groups under the evaluated assumptions, while MOAH containing three or more aromatic rings remained a concern because of genotoxic and carcinogenic potential. The distinction reinforces why purity and refining specifications are central rather than cosmetic details.
Mineral oil matters because it challenges the habit of assigning one identity to one CAS number. For complex petroleum substances, safety and function depend on composition, refining severity, viscosity, carbon-number distribution, and residual aromatic content. A bottle of pharmaceutical white mineral oil and an inadequately refined petroleum oil may share historical vocabulary but not toxicological meaning. The story of mineral oil is therefore really a story about analytical specification: when a material is a mixture, knowing what has been removed can be just as important as knowing what remains.
References:
EFSA CONTAM Panel. EFSA Journal. 2023;21:e08215. DOI: 10.2903/j.efsa.2023.8215.
EFSA ANS Panel. EFSA Journal. 2013;11:3073. DOI: 10.2903/j.efsa.2013.3073.
EFSA. High viscosity white mineral oils. EFSA Journal. 2009;7:1387. DOI: 10.2903/j.efsa.2009.1387.
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