Carrageenans (E407) are a group of long, flexible polysaccharide chains (a type of carbohydrate) that are extracted from red edible seaweeds and have been used as a food additive for hundreds of years.
Its curling, helical structures allows carrageenan to form a gel at room temperature which has led to its widespread use as a gelling agent in both the human and pet food industries. In human food, carrageenan can be found in all sorts of foods from soy milk and yogurt to ready-meals and deli meats. In pet food, carrageenan is generally only found in firm wet foods like patés and 'loaf' foods.
Carrageenan is used as a gelling agent to give paté and loaf type wet pet foods their characteristic firm consistency. While there are a number of alternative gelling agents (agar-agar, konjac and alginate), carrageenan is by far the most popular amongst wet pet food producers.
Carrageenan is often used in conjunction with thickeners like cassia gum, guar gum or locust bean gum. These thickeners enhance the strength of gelling agents like carrageenan.
Despite its widespread use and long heritage, carrageenan has attracted considerable criticism from certain quarters of the scientific community.
A number of studies  have linked food grade carrageenan (also known as un-degraded carrageenan or just CGN) to gastrointestinal inflammation as well as higher rates of intestinal lesions, ulcerations, and even tumours. Degraded carrageenan (sometimes called poligeenan or dCGN), though, is far more potent. It is a known carcinogen and is routinely used to induce inflammation in lab animals so that scientists can test anti-inflammation drugs. While degraded carrageenan is not permitted in pet food, there is concern that some food grade carrageenan may be contaminated with dCGN  and also that the acid environment of the stomach may degrade food-grade carrageenan to form dCGN .
HOWEVER, for every study suggesting carrageenan could be problematic, there is another indicating that it is perfectly safe. Although many of the more pro-carrageenan studies are funded by and in many cases directly carried but by carrageenan producers (Celtic Colloids, FMC) or their affiliates (Toxpertise, Iontox), they are still subject to peer review and not without merit. In particular, a comprehensive review carried out in 2014 concluded that no studies to date had adequately demonstrated any carcinogenic, tumour promoter, genotoxic, developmental or reproductive effects from consuming food grade carrageenan .
Most significantly, in 2018 the European Food Safety Authority carried out its own investigation into carrageenan and found no adverse effects from carrageenan in rats all the way up to 7,500 mg/kg of body weight per day, which is WAY more than is found in pet foods and was the highest dose tested . They did, however, express some uncertainties over the general lack of reliable information on the additive's effects and suggested more work was necessary before they could be 100% sure of its safety.
Which foods contain carrageenan?
As mentioned above, carrageenan is generally only used in paté and loaf type wet pet foods.
Unfortunately, without your own lab, figuring out whether any specific paté or loaf food contains carrageenan can be very difficult.
Firstly, since it is a technological additive and only needs to be added in very small amounts, carrageenan does not have to be declared by the manufacturer so just because it is not on the label does not mean it's not in the food. The manufacturer is also under no obligation to tell you, even if you ask them directly.
Secondly, the pet food company itself might not even know that its foods contain carrageenan. This is because many wet food producers outsource their manufacturing to third party factories who may add carrageenan (most often as a component of the vitamin and mineral premix) without specifically notifying the producer. Some factories even actively withhold information like this from their client companies.
We have tried to find out which paté and loaf wet foods do and do not contain carrageenan and we have added each brand's response to its product review pages. Where the information was not forthcoming, we have added the phrase 'not guaranteed carrageenan free by the manufacturer'. Unfortunately, though, we have the same problems in verifying this information as anyone else so while we can pass on their responses in good faith, we cannot guarantee their veracity.
Carrageenan is certainly not the worst additive in pet food and for most dogs, the very small amount used is not likely to cause any upsets at all but we do still think caution is warranted. If your dog has a history of digestive upsets, it may well be best to look for a food that is free from carrageenan and other similarly controversial ingredients. Changing the diet up every so often would also help to limit the chances of carrageenan or any associated issues from building up in the dog's system over time.
If you do decide to avoid carrageenan, due to the total lack of transparency over its usage, the only way to be 100% sure would be to steer clear of firm wet foods like patés and loaf foods altogether.
Review of Harmful Gastrointestinal Effects of Carrageenan in Animal Experiments. Tobacman JK. Environmental Health Perspectives 109(10): 983-994. 2001. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1242073/
Exposure to common food additive carrageenan leads to reduced sulfatase activity and increase in sulfated glycosaminoglycans in human epithelial cells. Yang B, Bhattacharyya S, Linhardt R and Tobacman JK. Biochimie 94(6): 1309-16. 2012. https://www.ncbi.nlm.nih.gov/pubmed/22410212
Exposure to the common food additive carrageenan leads to glucose intolerance, insulin resistance and inhibition of insulin signalling in HepG2 cells and C57BL/6J mice. Bhattacharyya S, O-Sullivan I, Katyal S, Unterman T and Tobacman JK. Diabetologia 55(1): 194-203. 2012. https://www.ncbi.nlm.nih.gov/pubmed/22011715
Molecular weight distribution of carrageenans studied by a combined gel permeation/inductively coupled plasma (GPC/ICP) method. Yoshitaka Uno, Toshio Omoto, Yasunori Goto. Food Additives & Contaminants. 2010. https://www.tandfonline.com/doi/abs/10.1080/02652030117235
Food additive carrageenan: Part I: A critical review of carrageenan in vitro studies, potential pitfalls, and implications for human health and safety. McKim JM. Critical Reviews in Toxicology 44(3): 211-43. 2014. https://www.ncbi.nlm.nih.gov/pubmed/24456237
Food additive carrageenan: Part II: A critical review of carrageenan in vivo safety studies. Weiner ML. Critical Reviews in Toxicology 44(3): 244-69. 2014. https://www.ncbi.nlm.nih.gov/pubmed/24467586
Re?evaluation of carrageenan (E 407) and processed Eucheuma seaweed (E 407a) as food additives. EFSA Panel on Food Additives and Nutrient Sources added to Food (ANS). EFSA Journal. 2018. https://efsa.onlinelibrary.wiley.com/doi/full/10.2903/j.efsa.2018.5238
Find foods containing Carrageenan See the full Ingredient Glossary