There are two main proteins in cow’s milk that can cause an allergic reaction:
- Casein, found in the solid part (curd) of milk that curdles
- Whey, found in the liquid part of milk that remains after milk curdles
You or your child may be allergic to only one milk protein or both. These proteins may be hard to avoid because they’re also in some processed foods. And, most people who react to cow’s milk will react to sheep’s, goat’s and buffalo’s milk. Less commonly, people allergic to cow’s milk are also allergic to soy milk.