Essential fatty acids are polyunsaturated fatty acids required in the diet as they cannot be synthesized de novo by humans. Key examples include linoleic acid (omega-6) and alpha-linolenic acid (omega-3). They serve as structural components of phospholipids in cell membranes, precursors for eicosanoids regulating inflammation and blood pressure, and support neurological development and cardiovascular health. Common dietary sources are vegetable oils, nuts, seeds, and fatty fish. Deficiency leads to dermatitis, growth issues, and impaired immunity. They are lipids with multiple cis double bonds conferring fluidity to membranes.