Essential fatty acids, such as linoleic, linolenic, and arachidonic acids, cannot be produced by the body; therefore, they must be obtained through food. They can be found in vegetable oils, plant seeds, green leafy vegetables, soybeans, meats, eggs, and fish. They are important as a major constituent of the stratum corneum, helping to maintain the skin barrier. They also serve as substrates necessary for the synthesis of other fatty acids, including those required for the synthesis of prostaglandins and leukotrienes, which play important roles in inflammation.

Essential fatty acid deficiency is rare, as almost all diets contain adequate amounts. It can be caused by gastrointestinal disorders or surgeries resulting in fat malabsorption, long-term parenteral nutrition without lipid supplementation, extremely low-fat diets, anorexia nervosa, alcohol use disorder, cystic fibrosis, and nephrotic syndrome. In most instances, this deficiency is associated with other nutritional deficiencies, such as kwashiorkor and marasmus. Because of their increased metabolic needs, infants – especially premature infants – are also at risk. Infants may be fed a diet low in essential fatty acids if given cow's milk.

The diagnosis is made based on clinical and laboratory features. The skin appears dry, scaly, and leathery with erythema. Intertriginous erosions, alopecia, hypopigmented hair, and petechiae may also be seen. Systemic features include failure to thrive, growth retardation, poor wound healing, thrombocytopenia, impaired reproductive health, abnormal liver and kidney function, increased susceptibility to infections, and neurologic damage.

The diagnosis can be made by measuring plasma linoleic, linolenic, arachidonic, and icosatrienoic acids.

The prognosis depends on the severity and coexistence of other nutritional deficiencies.