Stearic Acid
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Product Description
Stearic acid is a long-chain saturated fatty acid that appears as a white, waxy solid and is insoluble in water but readily dissolves in organic solvents. With its 18-carbon backbone ending in a carboxylic acid group, this low-polarity molecule is prized for the way it couples a hydrophobic tail to a polar head, allowing it to serve simultaneously as an emulsifier, thickener, lubricant and stabilizer. These dual characteristics make stearic acid a ubiquitous ingredient across industries: it thickens creams and lotions in cosmetics, acts as a tablet lubricant and excipient in pharmaceuticals, provides the firm texture and slow burn demanded in candles and soaps, and is converted into metal stearates that keep plastics, rubbers and even construction materials workable. Recent research has extended its relevance from formulation aid to bioactive agent: dietary stearic acid influences energy metabolism, cardiovascular signaling and even neuro-protection, while nanoparticles built from the acid enhance skin hydration and drug delivery. Whether it is slowing the combustion of energetic additives, mitigating shrinkage in green concretes, or forming the protective lipid matrix of the skin barrier, stearic acid continues to prove that a simple “hard fat” can play remarkably versatile roles in health, manufacturing and materials science.
Other Information
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Biological and Physiological Roles:
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A primary substrate for the enzyme Stearoyl-CoA Desaturase (SCD-1), which converts it to the monounsaturated fatty acid, oleic acid (C18:1).
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Regulates membrane rigidity and skin barrier function by influencing lipid packing in the stratum corneum.
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Influences cell signaling, secretion, and energy metabolism.
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Synthesis and Production
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Endogenous Biosynthesis (in humans/animals):
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Synthesized in the cytoplasm from acetyl-CoA.
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Pathway: Acetyl-CoA is first converted to palmitic acid (C16:0) via the fatty acid synthase complex. Palmitic acid is then elongated to stearic acid (C18:0) by microsomal fatty acid elongases (ELOVL family).
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Industrial Production & Extraction:
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Primarily obtained from the saponification or hydrolysis of animal and vegetable fats and oils, followed by separation and purification processes.
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Uses and Applications
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Animal Nutrition (Ruminant Feed):
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A key component of rumen-bypass fatty acid compositions (as per European Patent EP 3 273 793 B1).
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Used to form a protective, inert outer layer in encapsulated particles, protecting nutrients like amino acids from degradation in the rumen while allowing for release in the intestines. This improves milk yield, milk fat, and milk protein in lactating ruminants.
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Cosmetics and Personal Care:
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Functions: Used as an emulsifier, thickener, emollient, and surfactant.
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Applications: A major ingredient in moisturizers, shower gels, creams, lotions, deodorants, and lipsticks.
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Advanced Delivery Systems: A key building block for Solid Lipid Nanoparticles (SLN) and Nanostructured Lipid Carriers (NLC), where it improves stability, active-loading capacity, and is biocompatible with no skin irritation.
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Pharmaceuticals:
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Used as an excipient, primarily as a lubricant in the production of tablets and capsules (e.g., Magnesium Stearate).
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Serves as a critical material in drug delivery systems, such as lipid nanoparticles, for encapsulating active ingredients.
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Industrial and Manufacturing:
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Soaps and Detergents: The primary raw material for producing sodium stearate (bar soap) and potassium stearate (liquid soap).
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Plastics and Rubber: Acts as a lubricant and release agent during processing.
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Candles: Used as a hardener to make candles burn longer and slower.
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Textiles and Metal Processing: Used as a softening agent for textiles and in metal polishes and protective coatings.
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Human Health and Nutrition:
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Physiological Roles: Serves as an energy source (via β-oxidation), a structural component of triglycerides and phospholipids, and a modulator of cell membrane fluidity and stability.
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Unique Health Effect: Unlike most saturated fats, stearic acid is neutral regarding cholesterol; it does not raise plasma total or LDL cholesterol and may even lower it.
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Skin Health: Essential for skin barrier function, reducing transepidermal water loss and forming a protective hydrophobic film.
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Research Areas: Its role is being studied in metabolic syndrome, cardiovascular disease, diabetes, and other conditions, with context-dependent protective or deleterious effects.
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Chemical and Physical Properties
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Chemical Identity:
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Systematic Name: Octadecanoic acid
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Molecular Formula: C₁₈H₃₆O₂ / CH₃(CH₂)₁₆COOH
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Classification: Long-chain, straight-chain saturated fatty acid (SFA), C18:0 (no double bonds).
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Physical & Chemical Properties:
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Appearance: White, waxy solid at room temperature.
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Melting Point: ~69–70°C (for pure form); a key functional property, with a melting point of ≥ 40°C specified for rumen-bypass applications.
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Boiling Point: ~361°C.
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Iodine Value: ≤ 45 (a measure of low unsaturation, required for specific industrial applications like rumen-bypass fat).
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Solubility: Insoluble in water; soluble in organic solvents (alcohol, ether, chloroform).
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Reactivity: Can form salts (stearates) with metals and esters with alcohols. The carboxyl group (-COOH) is polar and hydrophilic, while the long hydrocarbon chain is non-polar and hydrophobic, giving it surfactant properties.
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Natural Occurrence:
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Dietary Sources: Abundant in animal fats (tallow, lard: 10–35%), cocoa butter, shea butter, and milk fat (5–15% of total fat). It is the second most consumed SFA in the U.S. diet.
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Endogenous Presence: Constitutes ~16–20% of circulating free fatty acids in human blood and is a major component of the lipids in the human stratum corneum (outer skin layer).
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Safety and Handling
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Regulatory Status: Generally Recognized As Safe (GRAS) for use in food and cosmetics.
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Toxicity: Considered to have low toxicity.
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Skin Irritation: Generally non-irritating and non-sensitizing, as confirmed by human patch tests on SLN/NLC formulations. May cause irritation only in very sensitive individuals.
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Environmental Impact: Biodegradable with a low bioaccumulation potential.