Carrageenan is a thickener and stabilizer extracted from red seaweed (including Irish moss). It's used to keep chocolate milk from separating, give dairy-free yogurts and nut milks a creamy body, and stabilize deli meats, ice cream, and some pouch snacks. The FDA classifies food-grade carrageenan as GRAS (Generally Recognized As Safe), and it's been used in the food supply for decades — it's technically a plant-derived, seaweed-based ingredient, which is why it appears in many "natural" and organic products.
The controversy centers on a distinction between two forms. Food-grade (undegraded) carrageenan is the approved ingredient. Degraded carrageenan, called poligeenan, is a different, lower-molecular-weight compound that is classified as a possible carcinogen and is not approved for food. Critics argue food-grade carrageenan can partially degrade or cause gut inflammation; industry and the FDA maintain the food-grade form is safe. The evidence in humans — and especially in children — is unsettled, which is why we tag it "limited" rather than "avoid."
Two regulatory signals are worth knowing. The EU prohibits carrageenan in infant formula as a precaution, and the US removed it from most infant formula years ago. In 2018, the USDA National Organic Standards Board voted to remove carrageenan from the list of substances allowed in organic food, though the USDA ultimately kept it available — so you'll still find it in some organic products. For kids, carrageenan isn't an added sugar or a dye; it's a texture ingredient, and the practical question is whether you prefer products that skip it.
How to spot it on a label: "Carrageenan," "Irish moss extract," or the EU code E407. It's most common in chocolate and flavored milks, dairy-free yogurts and nut/oat milks, cottage cheese, ice cream, and some pouch and deli products. Many brands now advertise "no carrageenan" on the front of the package; unsweetened plant milks from brands that skip gums and stabilizers are the easiest way to avoid it.