Essential fatty acid is one which is not synthesized by the organism and taken from outside.
Linolenic, linoleic and arachidonic acids are essential fatty acids. They occur in only low quantities in meat and milk. Essential fatty acids are abundant in plant food, fishes and fowl. Linolenic acid is precursor of arachidonic acid which in turn is precursor of prostaglandins and thromboxanes.
Deficiency of essential fatty acids causes sterilety, kidney failure and skin lesions (follicular hyperkeratosis).