Carrageenan is a naturally occurring family of carbohydrates extracted from red seaweed. This particular type of seaweed is common in the Atlantic Ocean near Britain, Europe and North America. The seaweed is boiled to extract the carrageenan.
Carrageenan is widely used as an additive by the food industry for its gelling, thickening and stabilising properties.

Used in salad dressings, prepared meat and fish, flavoured milk, processed cheese, ice cream, evaporated milk, cream, cottage cheese, sour cream, infant formula, alcoholic beverages, sauces and dressings.

Known adverse effects include gastrointestinal ulcers (but it is also used to treat ulcers in humans) liver damage, effects on the immune system and it is suspected to cause cancer.

The type of carrageenan that can be added to food in the EU is very specific. It must not be in a chemically degraded (hydrolysed) form. A recent review of animal studies suggested that degraded carrageenan may be associated with cancer in the gastrointestinal tract. But comparable evidence does not exist in humans. The Food Standards Agency in the UK is currently carrying out toxicological research on carrageenan and is developing a method to measure levels of this additive in food.