The first indication that dietary fat may be essential for healthy growing animals was presented in 1918 by Aron, who proposed that butter has a nutrient value that cannot be provided by other dietary components
1
. This report suggested that there was a special nutritive value inherent in fat apart from its caloric contribution and that this possibly was related to the presence of certain lipids. In 1929, Burr and Burr
2
presented the first in a series of papers outlining a “new deficiency disease produced by the rigid exclusion of fat from the diet.” They developed the hypothesis that warm-blooded animals in general cannot synthesize appreciable quantities of certain fatty acids. In 1930, both investigators significantly added to their earlier work by presenting evidence that the dietary inclusion of linoleic acid alone could reverse all deficiency symptoms resulting from a fat-free diet and thus linoleic acid (LA or 18:2n-6
2
) was heralded as an “essential fatty acid” (EFA)
3
. This pioneering study contained additional observations which indicated that besides the visible scaliness of the skin, animals with essential fatty acid deficiency (EFA-deficiency) also experience increased water consumption without increased urine output leading to speculation of increased water loss through the skin. Thus, Burr recognized in these early studies the two major defects that have been associated with EFA deficiency in cutaneous biology, namely: epidermal hyperproliferation and an increased permeability of the skin to water.
Structural Forms
Three major families of unsaturated fatty acids (UFAs) are characteristic of mammalian species: the n-9, the n-6, and the n-3 UFAs. The n-6 and n-3 polyunsaturated fatty acids (PUFAs) are defined by the position of the double bond closest to the terminal methyl group of the fatty acid molecule.
