C18:2 (Lipid numbers)
|Molar mass||280.45 g·mol−1|
−5 °C (23 °F)
−12 °C (10 °F)
230 °C (446 °F) at 21 mbar
230 °C (446 °F) at 16 mmHg
|Vapor pressure||16 Torr at 229 °C|
|Flash point||112 °C (234 °F)|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|(: / ?)|
Linoleic acid (LA) is a polyunsaturated omega-6 fatty acid. It is a colorless liquid at room temperature. In physiological literature, it has a lipid number of 18:2 cis,cis-9,12. From the chemistry perspective, linoleic acid is a carboxylic acid with an 18-carbon chain and two cis double bonds; with the first double bond located at the sixth carbon from the methyl end.
Linoleic acid belongs to one of the two families of essential fatty acids, which means that the human body cannot synthesize it from other food components.
The word "linoleic" derived from the Greek word linon (flax). Oleic means "of, relating to, or derived from oil of olive" or "of or relating to oleic acid" because saturating the omega-6 double bond produces oleic acid.
In physiology 1
- Metabolism and eicosanoids 1.1
- Industrial uses 2.1
- Use in research 2.2
- Dietary sources 3
- See also 4
- References 5
- External links 6
LA is a polyunsaturated fatty acid used in the biosynthesis of arachidonic acid (AA) and thus some prostaglandins, leukotrienes (LTA, LTB, LTC), and thromboxane (TXA). It is found in the lipids of cell membranes. It is abundant in many nuts, fatty seeds (flax seeds, hemp seeds, poppy seeds, sesame seeds, etc.) and their derived vegetable oils; comprising over half (by weight) of poppy seed, safflower, sunflower, corn, and soybean oils.
Linoleic acid is an essential fatty acid that must be consumed for proper health. A diet only deficient in linoleate (the salt form of the acid) causes mild skin scaling, hair loss, and poor wound healing in rats.
Along with oleic acid, linoleic acid is released by cockroaches upon death which has the effect of preventing other roaches from entering the area. This is similar to the mechanism found in ants and bees, which release oleic acid upon death.
Metabolism and eicosanoids
There is evidence suggesting that infants lack Δ6desaturase of their own, and must acquire it through breast milk. Studies show that breast-milk fed babies have higher concentrations of GLA than formula-fed babies, while formula-fed babies have elevated concentrations of LA.
GLA is converted to dihomo-gamma-linolenic acid (DGLA), which in turn is converted to arachidonic acid (AA). One of the possible fates of AA is to be transformed into a group of metabolites called eicosanoids during the inflammatory response and during physical activity; eicosanoids are a class of paracrine hormones. The three types of eicosanoids are prostaglandins, thromboxanes, and leukotrienes. Eicosanoids produced from AA tend to promote (not cause) inflammation and promote growth during and after physical activity in healthy humans. For example, both AA-derived thrombaxane and leukotrieneB4 are proaggregatory and vasoconstrictive eicosanoids during inflammation. The oxidized metabolic products of linoleic acid, such as 9-hydroxyoctadecanoic acid and 13-hydroxyoctadecanoic acid, have also been shown to activate TRPV1, the capsaicin receptor, and through this might play a major role in hyperalgesia and allodynia.
An increased intake of certain  omega–3 fatty acids with a decrease in omega-6 fatty acids has been shown to attenuate inflammation due to reduced production of these eicosanoids.
One study monitoring two groups of survivors of myocardial infarction concluded “the concentration of alpha-linolenic acid was increased by 68%, in the experimental group, and that of linoleic acid reduced by 7%...the survivors of a first myocardial infarction, assigned to a Mediterranean alpha-linolenic acid rich diet, had a markedly reduced rate of recurrence, other cardiac events and overall mortality.” 
Linoleic acid is used in making quick-drying oils, which are useful in oil paints and varnishes. These applications exploit the easy reaction of the linoleic acid with oxygen in air, which leads to crosslinking and formation of a stable film.
Linoleic acid has become increasingly popular in the beauty products industry because of its beneficial properties on the skin. Research points to linoleic acid's anti-inflammatory, acne reductive, and moisture retentive properties when applied topically on the skin.
Use in research
Linoleic acid lipid radicals can be used to show the antioxidant effect of natural phenols. Experiments on linoleic acid subjected to 2,2′-azobis (2-amidinopropane) dihydrochloride induced oxidation of linoleic acid; hence producing lipid radicals and then the use of different combinations of phenolics show that binary mixtures can lead to either a synergetic antioxidant effect or to an antagonistic effect towards the lipid radicals. Research like this is useful in discovering which phenols prevent the autoxidation of lipids in vegetable oils.
Note: Unless cited, none of these percentages have been verified by scientific research.
|Evening Primrose oil||73%|
|Grape seed oil||69.6%|
|Barbary Fig Seed Oil||65%|
|Wheat germ oil||55%|
|Rice bran oil||39%|
|Olive oil||10% (3.5 - 21%)|||
- Conjugated linoleic acid
- Omega-6 fatty acid: Negative health effects
- Essential fatty acids
- Essential fatty acid interactions
- Essential nutrients
- The Merck Index, 11th Edition, 5382
- 60-33-3Record of CAS RN in the GESTIS Substance Database of the IFA
- David J. Anneken, Sabine Both, Ralf Christoph, Georg Fieg, Udo Steinberner, Alfred Westfechtel "Fatty Acids" in Ullmann's Encyclopedia of Industrial Chemistry, 2006, Wiley-VCH, Weinheim. doi:10.1002/14356007.a10_245.pub2
- Burr, G.O., Burr, M.M. and Miller, E. (1930). "On the nature and role of the fatty acids essential in nutrition" (PDF). J. Biol. Chem. 86 (587): 1–9.
- "Nutrient Data Laboratory Home Page". USDA National Nutrient Database for Standard Reference, Release 20. U.S. Department of Agriculture, Agricultural Research Service. 2007.
- Cunnane S, Anderson M (1 April 1997). C) linoleate oxidation"14"Pure linoleate deficiency in the rat: influence on growth, accumulation of n-6 polyunsaturates, and (1-. J Lipid Res 38 (4): 805–12.
- Ruthig DJ & Meckling-Gill KA. (1 October 1999). "Both (n-3) and (n-6) fatty acids stimulate wound healing in the rat intestinal epithelial cell line, IEC-6". Journal of Nutrition 129 (10): 1791–8.
- "Earth News: Ancient 'smell of death' revealed". BBC.
- David F. Horrobin (1993). "Fatty acid metabolism in health and disease: the role of Δ-6-desaturase". American Journal of Clinical Nutrition 57: 732S–7S.
- Piomelli, Daniele (2000). "Arachidonic Acid". Neuropsychopharmacology: The Fifth Generation of Progress. Retrieved 2009-04-16.
- Patwardhan, AM; Scotland, PE; Akopian, AN; Hargreaves, KM (2009). "Activation of TRPV1 in the spinal cord by oxidized linoleic acid metabolites contributes to inflammatory hyperalgesia". Proceedings of the National Academy of Sciences of the United States of America 106 (44): 18820–4.
- Kinsella, JE; Lokesh, B; Stone, RA (1990). "Dietary n-3 polyunsaturated fatty acids and amelioration of cardiovascular disease: possible mechanisms". The American journal of clinical nutrition 52 (1): 1–28.
- Kinsella, John E.; Lokesh, Belur; Stone, Richard A. (1990). "Dietary n-3 polyunsatruated fatty acids and amelioration of cardiovascular disease: possible mechanisms". American Journal of Clinical Nutrition 52 (1): 1–28.
- de Lorgeril, M; Renaud, Serge; Salen, P; Monjaud, I; Mamelle, N; Martin, J.L.; Guidollet, J; Touboul, P; Delaye, J (1994). "Mediterranean alpha-linolenic acid-rich diet in secondary prevention of coronary heart disease". Lancet 343: 8911.
- Diezel, W.E.; Schulz, E.; Skanks, M.; Heise, H. (1993). "Plant oils: Topical application and anti-inflammatory effects (croton oil test)". Dermatologische Monatsschrift 179: 173.
- Letawe, C; Boone, M; Pierard, GE (March 1998). "Digital image analysis of the effect of topically applied linoleic acid on acne microcomedones". Clinical & Experimental Dermatology 23 (2): 56–58.
- Darmstadt, GL; Mao-Qiang, M; Chi, E; Saha, SK; Ziboh, VA; Black, RE; Santosham, M; Elias, PM (2002). "Impact of topical oils on the skin barrier: possible implications for neonatal health in developing countries". Acta Paediatrica 91 (5): 546–554.
- Peyrat-Maillard, M. N.; Cuvelier, M. E.; Berset, C. (2003). "Antioxidant activity of phenolic compounds in 2,2′-azobis (2-amidinopropane) dihydrochloride (AAPH)-induced oxidation: Synergistic and antagonistic effects". Journal of the American Oil Chemists' Society 80 (10): 1007–1012.
- Janet Raloff (2012). "Tricks Foods Play". Science News Magazine 182 (7): 25–28.
- Oil, peanut, salad or cooking: search for peanut oil on http://www.nal.usda.gov/fnic/foodcomp/search/
- M. K. Nutter, E. E. Lockhart and R. S. Harris (1943). "The chemical composition of depot fats in chickens and turkeys". Journal of the American Oil Chemists' Society 20 (11): 231–234.
- "Olive Oil : Chemical Characteristics".
- Beltran; Del Rio, C; Sánchez, S; Martínez, L (2004). "Influence of Harvest Date and Crop Yield on the Fatty Acid Composition of Virgin Olive Oils from Cv. Picual" (PDF). J. Agric. Food Chem. 52 (11): 3434–3440.
- Linoleic acid MS Spectrum
- Fatty Acids: Methylene-Interrupted Double Bonds, AOCS Lipid Library