Between 1930 and 1950, arachidonic acid and linolenic acid were termed essential because each was more or less able to meet the growth requirements of rats given fat-free diets. In the 1950s Arild Hansen showed that in humans: infants fed skimmed milk developed the essential fatty acid deficiency. It was characterized by an increased food intake, poor growth, and a scaly dermatitis, and was cured by the administration of corn oil. Later work by Hansen randomized 426 children to four treatments: modified cows milk formula, skimmed milk formula, skimmed milk formula with coconut oil, or cows milk formula with corn oil. The infants who received the skimmed milk formula or the formula with coconut oil developed essential fatty acid deficiency signs and symptoms. This could be cured by administration of ethyl linoleate (the ethyl ester of linoleic acid) with about 1% of the energy intake.Collins et al. 1970 were the first to demonstrate linoleic acid deficiency in adults. They found that patients undergoing intravenous nutrition with glucose became isolated from their fat supplies and rapidly developed biochemical signs of essential fatty acid deficiency (an increase in 20:3n-9/20:4n-6 ratio in plasma) and skin symptoms. This could be treated by infusing lipids, and later studies showed that topical application of sunflower oil would also resolve the dermal symptoms. Linoleic acid has a specific role in maintaining the skin water-permeability barrier, probably as constituents of acylglycosylceramides. This role cannot be met by any ω-3 fatty acids or by arachidonic acid.
Essential fatty acids, or EFAs, are fatty acids that humans and other animals must ingest because the body requires them for good health but cannot synthesize them.The term "essential fatty acid" refers to fatty acids required for biological processes but does not include the fats that only act as fuel. Essential fatty acids should not be confused with essential oils, which are "essential" in the sense of being a concentrated essence. Only two fatty acids are known to be essential for humans: alpha-linolenic acid (an omega-3 fatty acid) and linoleic acid (an omega-6 fatty acid). Some other fatty acids are sometimes classified as "conditionally essential", meaning that they can become essential under some developmental or disease conditions; examples include docosahexaenoic acid (an omega-3 fatty acid) and gamma-linolenic acid (an omega-6 fatty acid). When the two EFAs were discovered in 1923, they were designated "vitamin F", but in 1929, research on rats showed that the two EFAs are better classified as fats rather than vitamins. Functions
The biological effects of the ω-3 and ω-6 fatty acids are mediated by their mutual interactions, see Essential fatty acid interactions for detail.In the body, essential fatty acids serve multiple functions. In each of these, the balance between dietary ω-3 and ω-6 strongly affects function.