Milk allergy

What it is

A milk allergy happens when the immune system reacts to milk and dairy products as though they were a dangerous invader.¹ Milk has two main kinds of protein. Casein, the solid part of milk, makes up about 80 percent of its protein, and whey, in the liquid part, makes up the other 20 percent.¹

Milk is one of the most common food allergens, particularly in children: between 2% and 3% of children younger than 3 are allergic to it.¹ FARE calls cow’s milk allergy the most common food allergy in infants and young children.⁴ Many children outgrow it, though more slowly than experts once thought. In one study, fewer than 20% had outgrown it by age 4, while about 80% are likely to outgrow it before age 16.¹

People allergic to cow’s milk may also be allergic to milk from other animals, including sheep and goats.¹

A milk allergy is not lactose intolerance. Lactose intolerance means digestive symptoms, such as bloating, diarrhea and gas, after eating or drinking lactose, a sugar found naturally in milk and milk products.³ A milk allergy, by contrast, is an immune system disorder.³ People with lactose intolerance cannot fully digest milk sugar because they lack enough lactase, the enzyme that breaks it down, and ACAAI says the two conditions are not related.¹

Symptoms it causes

Symptoms can begin within a short time after someone has milk or a milk protein.¹ They can include hives, an upset stomach, vomiting and, especially in infants, bloody stools.¹ FDA notes that food allergy symptoms may appear anywhere from a few minutes to a few hours after eating, and that a mild reaction does not always mean the allergy is mild.⁶

Reactions can range from mild, such as hives, to severe.⁴ The most serious is anaphylaxis, a life-threatening reaction that affects the whole body and can impair breathing.² ACAAI lists anaphylaxis as a rare reaction to milk, and names food allergies, milk among them, as the most common causes of anaphylaxis.¹ An allergist can test for a milk allergy.¹

Reading food labels

Milk is a major food allergen under US law. The Food Allergen Labeling and Consumer Protection Act of 2004 (FALCPA) named eight major food allergens, milk among them, and the FASTER Act made sesame the ninth, effective January 1, 2023.⁵

A packaged food that contains milk must name it in one of two ways: in parentheses after an ingredient, as in “whey (milk),” or in a “Contains” statement next to or right after the ingredient list, as in “Contains wheat, milk, and soy.”⁵ If an ingredient’s usual name already says milk, as buttermilk does, it does not need a separate mention.⁷ Not every product that contains an allergen has a “Contains” statement, so FDA points readers to the whole ingredient list.⁷

FDA counts milk from domesticated cows, goats, sheep and other ruminants as milk.⁸ For milk from an animal other than a cow, FDA says the label should also name the animal, as in “Contains milk, goat milk.”⁹

Phrases such as “may contain milk” or “produced in a facility that also uses milk” are advisory statements. FDA says they are not required by law. Manufacturers can use them for cross-contact that cannot be avoided, but only if they follow good manufacturing processes and have taken every precaution to avoid it, and the statements must be truthful and not misleading.⁵ FDA calls the “may contain” statement voluntary, and not all manufacturers use it.⁷

Milk protein can turn up in less obvious places. Casein, sodium caseinate and whey are all milk proteins.⁷ ACAAI notes that some canned tuna, sausage, meats and other nondairy products may contain casein, that beverage mixes and energy drinks commonly contain whey, and that milk protein has been found in some chewing gum.¹ FARE’s list of ingredient names that signal milk also includes ghee and lactoglobulin.⁴