Casein

Casein is the main protein in milk, roughly four fifths of it. Whey is most of the rest. Both are milk proteins, and an allergy to milk can involve either or both, which is why avoiding one is not a strategy.

Because casein sets into a gel and holds water and fat together, it is useful well beyond dairy products. It turns up in protein powders, processed meats, some breads, coffee whiteners and a long tail of manufactured food where you would not think to look for milk.

The “non-dairy” problem

This is the single most useful thing on this page.

In US labelling, “non-dairy” on the front of a package does not mean the product contains no milk protein. Non-dairy creamers containing sodium caseinate are the classic case, and they are not a loophole being exploited quietly: the milk source still has to be declared under allergen labelling rules, so the back of the pack tells the truth even when the front is misleading.

The lesson generalises. The front of a package is an advertisement and the ingredient list is a document, which is the whole argument of what “natural” and “clean” legally mean. For an allergen, always read the back.

The names it travels under

Casein. Caseinate. Sodium, calcium or potassium caseinate. Rennet casein. Casein hydrolysate. Milk protein concentrate or isolate. Curds. Some products list “lactalbumin” or “lactoglobulin”, which are whey proteins rather than casein but are still milk.

In the United States the food source must be declared, so milk will be named somewhere on the label even when the specific protein has an unfamiliar name. In the EU and UK, the allergen is emphasised inside the ingredient list itself.

Lactose is a different thing

Worth separating, because the two get conflated constantly and the consequences differ.

Lactose intolerance is a digestive problem with milk sugar. It is uncomfortable, it is dose-dependent, and lactose-free products, which have had the sugar broken down, are designed for it. Those products still contain casein.

Milk allergy is an immune response to milk protein. Lactose-free milk is not safe for it, because removing the sugar does nothing to the protein.

So “lactose-free” on a package answers a completely different question from the one a milk-allergic reader is asking. If you are reading labels for an allergy rather than for digestion, that phrase is not relevant to you.

Outside food

Casein and milk-derived proteins appear in some cosmetics and hair products as conditioning agents, where they are listed under INCI names rather than as “milk”. Reactions through skin contact are less common than through eating, but for a diagnosed milk allergy it is worth knowing that the ingredient crosses categories. Pura reads cosmetic labels against the same profile as food ones, which is the main reason we treat the three categories as one problem rather than three.