What it is
Lecithin is a fatty substance that works as an emulsifier, holding oil and water together and stopping chocolate from turning grainy. Chemically it is a mixture of phosphatides, the same family of molecules that build the membranes around living cells, which is why it turns up in living things of every kind. The version US regulators describe as generally safe is 'isolated as a gum following hydration of solvent-extracted soy, safflower, or corn oils', in other words squeezed from plants. Nature also packs lecithin into egg yolk, and food makers have pulled it from there for more than a century, so both plant and animal sources are real. When European safety reviewers looked at where E322 actually comes from, they found soya bean oil doing most of the work, with sunflower, rapeseed and egg yolk trailing behind as minor sources.
How to tell
Lecithin turns up in chocolate above almost anything else, then in bread and pastry glazes, margarine, plant milks, ice cream and mayonnaise. Here the law does vegans an accidental favour: soya and egg are both allergens that must be declared in the UK, EU and US, so lecithin from either source is usually spelled out as 'soya lecithin' or 'egg lecithin' rather than hidden. That means a bald 'lecithin' or 'E322' with no allergen warning is very often sunflower, which needs no declaration and is plant-derived. The place to stay alert is baked goods, glossy pastry glazes and some older confectionery recipes, where egg yolk lecithin has a long history. If a label lists only 'lecithin' and you want certainty, check the allergen line for egg, and when it is still unclear a quick message to the maker settles it.