Food allergies occur due to an abnormal immune response triggered by food allergens. Studies suggest that proteins such as beef, dairy, and fish in pet food are common allergens. However, some experts believe that the cause of allergic reactions is not the type of protein itself but rather the molecular size of the protein when it is absorbed in the digestive tract. Unlike food intolerance, food allergies affect both the digestive system and the skin, causing an abnormal immune reaction to an otherwise harmless food component.

Food intolerance refers to an adverse reaction to certain foods or ingredients, often caused by the inability to properly digest a specific component due to a lack of necessary enzymes. Common symptoms include bloating, diarrhea, and other gastrointestinal discomfort. Food intolerance shares some similarities with food allergies in terms of symptoms and causes. One well-known example is lactose intolerance, where a pet lacks the enzyme lactase, making it unable to digest lactose in dairy products. Another common form is gluten intolerance, which occurs when a pet cannot digest gluten-containing grains such as wheat, rye, barley, and oats.