What it is
E407 is carrageenan, a family of polysaccharides extracted from red seaweed (Chondrus crispus and others).
Why it matters
Thickener and gelling agent. Common in plant milks (the controversial choice for stabilising emulsions), ice cream, processed meats, infant formula, toothpaste.
What to do
Always vegan. Some plant-milk brands now avoid carrageenan because of separate (non-vegan) concerns about inflammation in animal studies — but the additive itself is wholly plant-sourced.