Docosahexaenoic acid — the full form of DHA — is the long-chain omega-3 fatty acid with 22 carbons and six double bonds, one of the most structurally important fats in the human body. It concentrates in the brain, the retina, and sperm membranes, where its extreme flexibility keeps cell membranes fluid and functional; the developing infant brain lays it down rapidly, which is why DHA features so heavily in pregnancy and infant nutrition. Oily fish — salmon, mackerel, sardines — are the richest dietary sources, with algae oils serving vegetarians and infant formula. The body can make small amounts from alpha-linolenic acid, but conversion is poor, so diet matters. DHA shares the omega-3 stage with EPA, but its role is architectural — building neural tissue — rather than primarily anti-inflammatory.